SpaceTime Series 27 Episode 30
*Unveiling the Mysteries of Dark Matter with Hypothetical Axion Stars
Could the enigmatic axion star hold the key to understanding dark matter? Join us as we delve into the realm of theoretical physics, where scientists are using the expected properties of these never-before-seen stars to potentially pinpoint the elusive components of dark matter. First proposed in 1977, axions are lightweight candidates for dark matter, and their discovery could illuminate both dark energy and the darkest secrets of the cosmos.
*Mars: A Barren Aquifer and the Quest for Ancient Groundwater
Mars' past as a wet world is etched into its surface, but a new study reveals that ancient Martian aquifers may have been surprisingly dry. Despite evidence of past water flow, researchers suggest that the red planet's southern highlands experienced minimal groundwater recharge. The implications? A vastly different water cycle from Earth's, challenging our search for life and resources on our neighboring world.
*The Cosmic Kitchen: Frying Food in Zero-G
Ever wondered if you could whip up a batch of crispy fries in space? We explore the physics of frying food in microgravity, where bubbles don't rise and steam behaves unexpectedly. Discover how scientists are reimagining cooking techniques for the final frontier, ensuring astronauts won't have to give up their comfort foods on long-duration missions.
*March Skywatch: Equinoxes, Constellations, and Celebrating Pi Day
March heralds the equinox, bringing nearly equal day and night, and setting the celestial stage for stargazing. We'll guide you through constellations like Taurus, Leo, and the river Eridanus, and remind you to mark your calendars for Pi Day. Plus, don't miss the planetary dance before dawn, as Mars, Venus, and Saturn put on a celestial show.
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This is Space Time Series 27 Episode 30 for broadcast on the
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8th of March 2024. Coming up on Space Time, could a hypothetical
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axion star pinpoint where and what dark matter is? A new study
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looking at Martian groundwater, and we pose the question, is it
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possible to fry food in space? All that and more coming up on
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Space Time.
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Welcome to Space Tiled with Stuart Garing.
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Thank you Thank you Astronomers plan on using the expected
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characteristics of a hypothetical type of star to
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improve their understanding of mysterious dark matter. The star
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is known as an axion star. It's never been seen, and even its
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component axions are just hypothetical.
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First theorized back in 1977, axions, if they exist, are light
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mass particles that could be a contender for dark matter due to
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the heat they should be giving off. However, due to the wide
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range of sizes and masses that there could possibly be, their
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potential discovery has remained elusive.
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Now a series of papers reported in the journal Physical Review
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Letters suggest that a new approach to locate this wonder
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particle if it exists could explain both dark energy and
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dark matter.
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One of the study's authors, Malcolm Fairburn from King's
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College London, says axions are one of the prime candidates for
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dark matter. Fairburn and colleagues theorized that they
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would have the capacity to heat the universe just like
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supernovae and ordinary stars after coming together in dense
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clumps.
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And it's those dense clumps that provide a target to search for.
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Einstein's general theory of relativity suggests that around
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85% of the material of the universe is dark matter, a
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mysterious invisible substance which scientists know exists
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because they can see its gravitational impact on ordinary
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baryonic matter.
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The stuff stars, planets, cars, people, dogs and cats are made
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out of. Observations show that something, some invisible
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matter, is preventing galaxies from spinning apart as they
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rotate. And that invisible matter has been named dark
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matter. But scientists have no idea what dark matter is, and
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the hypothetical axion particle is one of the contenders.
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Axions would be extremely low mass particles, but they must be
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present in very large numbers to explain the amount of dark
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matter which we infer from galaxies.
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Now, according to this new hypothesis, they could also be
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packed very densely into specific areas, meaning they're
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subject to the laws of quantum mechanics. And that would mean
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individual axions would begin to act in concert. That suggests
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there could be large groupings of axion, possibly as dark
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matter, at the centre of galaxies.
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And these could be the so-called axion stars that the authors are
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talking about. But these axion stars would become unstable once
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they moved beyond a certain mass threshold, exploding into the
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electromagnetic spectrum through radiation and photons.
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The authors suggest that these explosions have the potential to
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have heated the intergalactic gas that existed between
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galaxies in the time between the Big Bang 13.82 billion years ago
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and the formation of the first stars some 50 to 500 million
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years after the beginning of the universe, a period we refer to
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as the cosmic dark ages.
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Now all this would change the way the cosmic microwave
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background radiation will look during this period of time. The
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cosmic microwave background radiation is the leftover heat
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from the Big Bang, now cooled down to just 2.7 degrees above
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absolute zero.
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Scientists can observe this cosmic microwave background
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radiation through the hydrogen 21 centimeter measurement. So,
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by looking for signals of where axion stars might have exploded
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in the early or present universe, scientists may be able
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to use these methods to track down the so far unobserved axion
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and discover the sources of some, if not all, dark matter.
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Febern says coherent axion stars, even those which are
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relatively compact, have the potential to burst into a halo
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of electromagnetism and light. Knowing the kind of structures
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axion dark matter can form, and its impact on the surrounding
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intergalactic gas, could pave new ways for its detection.
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Being able to find axions would therefore help scientists and
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physicists solve one of science 's big questions over a century
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in the making, and at the same time help lay bare the history
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of the early universe.
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By computing the total number of axion stars in the universe, and
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by extension their latent explosive potential on
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intergalactic gas, the authors have also surmised the size of
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the signal that axion stars would give out in the cosmic
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microwave background radiation.
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And this would allow the 21cm measurements to categorise what
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is and what isn't originating from axions accurately, thereby
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aiding in the search. This is Space Time. Still to come, we
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look at the story of Martian groundwater, and we ask the
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question, would it be possible to fry foods in space? All that
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and more still to come on Space Time.
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Obrigado.
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Scientists studying the Red Planet Mars have begun searching
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for possible underground water supplies. But a new study
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predicts there'd be very little groundwater recharge in the
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ancient Martian aquifers. There 's plenty of evidence that Mars
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was once a warm, wet world.
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The geological record of the Red Planet shows evidence for water
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flooding across its surface, forming river deltas and valleys
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carved out by massive flash floods. In fact, much of the
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Martian Northern Hemisphere may once have been a giant Red
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Planet ocean.
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But a new study reported in the journal Icarus shows that no
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matter how much rainfall fell on the surface of ancient Mars, it
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seems very little of it seeped into an aquifer on the planet's
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southern highlands.
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Scientists made the discovery by modelling groundwater recharge
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dynamics for the aquifer using a range of methods from computer
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models to simple back-of-the-envelope
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calculations. But it turns out that no matter the degree of
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complexity, the results converged on the same answer, a
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minuscule 0.03 millimetres of groundwater recharge per year on
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average.
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That means that whatever rain fell in the model, only an
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average of 0.03 millimetres per year could have entered the
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aquifer and still produced the landforms remaining on the
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planet today.
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Now, for a comparison, the annual rate of groundwater
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recharge for the Trinity and Edwards Trinity Plateau
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aquifers, which provide water to San Antonio and Texas, generally
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ranges from 2.5 to 50 per year, or about 80 to 1 times more
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than the Martian aquifer recharge rate.
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The study's lead author Eric Hyatt from the University Of
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Texas at Austin says there's a variety of potential reasons for
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such a low groundwater flow rate. When it rains, the water
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may mostly have washed across the Martian landscape as runoff,
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or it may just not have rained very much on Mars at all.
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These findings can help scientists constrain the
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climatic conditions capable of producing rainfall on early
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Mars. They also suggest a very different water regime on the
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Red Planet compared to what exists on planet Earth today.
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Hyatt says the fact that the groundwater isn't as big of a
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process on Mars could mean that it just didn't rain very much on
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the Red Planet, or that runoff might simply be more important.
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What it does show is just how fundamentally different the two
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planets Earth and Mars really are. The models used in the
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study work by simulating groundwater flow in a
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steady-state environment where inflow and outflow of water into
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the aquifer is balanced.
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The study also incorporated modern topographical data
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collected by satellites. Hyatt says Mars still preserves one of
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the planet's oldest and most influential topographical
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features and extreme difference in elevation between the
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Northern Hemisphere lowlands and the Southern Hemisphere
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highlands, known as the Great Martian Dichotomy.
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And this dichotomy preserves signs of past groundwater
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upwelling in which groundwater rose up from the aquifer to the
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surface. The authors used geological markers of these past
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upwelling events to evaluate different model outputs.
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Understanding groundwater flow can help inform scientists of
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where to find water on Mars today. Whether you're looking
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for signs of ancient Martian life, or simply trying to
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sustain human explorers on the Red Planet, or making rocket
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fuel to get back home to Earth, it's essential to know where the
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Martian water is most likely to be.
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This is Space Time.
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Still to come, is frying food possible in space? And the March
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Equinox. The constellations Taurus, LEO, Corvus and
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Eridanus, and don't forget Pi Day, are among the harlots of
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the night skies on March Skywatch.
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Thank you.
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Well, if you like your fries and hash browns as much as I do,
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then there's one very obvious question that you ask yourself
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when it comes to space travel. Is it possible to fry foods in
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microgravity? And it's a legitimate question. You see,
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the food we eat determines how we feel, and as far as I'm
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concerned, nothing beats a good old fryer.
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Although in moderation, of course. As we prepare for
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missions to the moon and eventually onto Mars and beyond,
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astronauts will be happy to hear that one single comfort food is
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no longer out of reach, even in space, and that food is fries.
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Even though frying potatoes is done everywhere around the
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world, it involves complex physics and chemistry, and of
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course in space, everything becomes more complicated. You
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see, without gravity and therefore the buoyancy pulling
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upwards, bubbles might stick to the surface of the potato,
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shielding the potato in a layer of steam that might leave it
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undercooked.
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To study how microgravity influences cooking techniques
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such as frying, a novel experimental carousel-type
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apparatus was designed to be safe while also operating in
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microgravity conditions on a parabolic flight aboard a Vomit
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Comet airliner. The experiment filmed the frying process with a
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high-speed, high-resolution camera in order to capture the
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bubbling dynamics such as growth rate, size and distribution.
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As well as the escape velocity from the potato, the bubble's
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speed and direction of travel in the oil was also noted. The
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experiment also measured the temperature of the boiling oil,
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as well as the temperature inside the potato.
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Scientists reporting in the Food Research International Journal
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found that shortly after the potato was added to the oil in
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low-gravity conditions, vapor bubbles detached easily from the
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potato's surface, just like they do here on Earth. And that's got
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to be a good news story. This is Space Time.
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Time now to turn our eyes to the skies and check out the
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celestial sphere for March on Skywatch. Happy New Year! Well,
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it would be if this was ancient Mesopotamia or Rome. That's
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because March was the first month of the New Year, going
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back to the earliest concept of celebrating New Year's Day at
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the time of the vernal equinox, around 2000 BCE.
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See, the ancient Roman calendar, which had just 10 months,
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designated March 1st as the New Year. That 10-month calendar is
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still reflected today. With the name September or Septum being
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Latin for seven, October or Octo meaning eight, November or Novem
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Nine, and December or Deci meaning ten.
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It wasn't really until the Gregorian calendar that January
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1st marked the start of the New Year, but in the beginning it
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was mostly Catholic countries that adopted it. Protestant
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nations only gradually moved across, with the British, for
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example, not adopting the reformed calendar until 1752.
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Prior to that date, the British Empire and its American colonies
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still celebrated New Year's Day on March 25th.
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The highlight of the month is the March Equinox, which this
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year takes place at 14.06 in the afternoon of Wednesday, March
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20, Australian Eastern Daylight Time. That's 23.06 in the
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evening of Tuesday, March 19, US Eastern Daylight Time, and 3.06
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in the morning Greenwich Mean Time.
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For our listeners in the Northern Hemisphere, it means
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the vernal equinox, the start of spring. Although south of the
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equator, it's the autumnal equinox, meaning a move into
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autumn. The day marks the point in Earth's orbit around the Sun
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when the planet's rotational axis means the Sun will appear
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to rise exactly due east and set exactly due west to someone
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standing on the equator.
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It means almost equal hours of darkness and light. In fact, the
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very word equinox is derived from the Latin, meaning equus or
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equal, and nox meaning night. It all comes about because Earth's
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rotational axis is tilted at an angle of around 23.4 degrees in
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relation to the ecliptic, the plane created by Earth's orbit
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around the Sun.
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That axial tilt is always pointed at the same position in
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the Sky, regardless of Earth's orbital position around the Sun.
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So on any other day of the year, either the northern or Southern
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Hemisphere, it tilted more towards the Sun.
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But on the two Equinoxes, usually around March 21st and
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September 23rd each year, the The tilt of Earth's axis is
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directly perpendicular to the Sun's rays. However, there's a
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complication called precession. This causes Earth's spin axis to
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wobble ever so slightly, just like the axle of a spinning top.
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The rate of precession is only about half a degree per century,
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so people don't notice it on human timescales. And because
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the direction of Earth's axis of rotation determines at which
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point in Earth's orbit the seasons occur, precession will
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cause the particular season, for example the Southern Hemisphere
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autumn, to occur at a slightly different place from year to
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year over a 21 year cycle.
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At the same time, Earth's orbit itself is subjected to small
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changes called perturbations. See, Earth's orbit's an ellipse,
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and there's a slow change in its orientation which gradually
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shifts the point of perihelion, Earth's closest orbital position
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to the Sun.
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Now, these two effects, the precession of the axis of
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rotation and the change in the orbit's orientation, work
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together to shift the seasons with respect to perihelion. And
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because we use a calendar year that's aligned to the occurrence
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of the seasons, the date of perihelion gradually regresses
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through a 21 year cycle.
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And there's another complication. Australia and some
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of the other Commonwealth countries start their seasons on
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the first day of the month, what are referred to as
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meteorological seasons, rather than on the solstice season
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Equinoxes, which are referred to as astronomical seasons.
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So, that means Australia's autumn officially began on March
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1st, rather than on the day of the March Equinox.
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Meteorological seasons are used because it makes it easier for
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meteorologists and climatologists to break the
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seasons down into more exact three-month calendar groupings
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for comparing seasonal and monthly statistics.
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The moment of the March Equinox is also important in astronomy
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because it's used to define the celestial coordinate system of
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right ascension and declination. In astronomy, the celestial
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coordinate system is the astronomical equivalent to the
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latitude and longitudinal coordinates used on Earth's
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surface.
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It's used to specify the position of objects in
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three-dimensional space and the direction of those objects on
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the celestial sphere, the imaginary globe surrounding the
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Earth. In other words, it lets scientists determine the
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position of a celestial object, such as a satellite, a planet,
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stars, galaxies and so on.
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Right ascension, which uses the symbol Alpha, is the angular
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distance measured eastwards along the celestial equator from
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the vernal equinox. On the celestial sphere, it's analogous
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to terrestrial longitude. Declination, which uses the
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symbol delta, measures the angle north or south of the celestial
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equator, and so it's the celestial equivalent to
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terrestrial latitude.
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Marking the vernal equinox and setting the western evening Sky
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this time of year is one of the oldest recognized constellations
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in the heavens, Taurus The Bull, so named around 6 years ago.
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In Greek mythology, Taurus represents the king of the gods
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Zeus. Zeus lusted after King Agenor's daughter Europa, who
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was looking after a herd of cattle. Now being a god and with
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godlike powers, Zeus decided to transform himself into a
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powerful white bull so that he could get closer to the
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beautiful Europa.
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Now once transformed into a bull, Zeus convinced Europa to
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climb on his back and he then carried her off to the island of
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Crete. Taurus's head is represented by a dominant
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V-shaped grouping of stars. The bright reddish star in the group
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is Aldebaran, an orange giant one and a half times the mass of
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the Sun located 65 light years away. A light year is about 10
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trillion kilometres.
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The distance a photon can travel in a year at 300 kilometres
00:17:43
per second, the speed of light in a vacuum, and the ultimate
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speed limit of the universe. Aldebaran is the 14th brightest
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star in the night Sky and the closest bright star to the point
00:17:53
of the vernal equinox.
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In ancient Arabic, Aldebaran's name means the follower, as it
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appears to follow the seven sisters of the Pleiades. It's
00:18:02
also the first of the four Royal or Guardian stars identified by
00:18:06
the ancient Mesopotamians. Now that V-shaped grouping of stars
00:18:10
near Ulubaran is known as the Hyades. It's the nearest young
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open star cluster to Earth, located just 153 light years
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away.
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Between Aldebaran and the Orion constellation, you'll see a
00:18:22
bright red star. That's Betelgeuse, the ninth brightest
00:18:25
star in the night Sky, these days more commonly called
00:18:28
Betelgeuse.
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If you turn to the north now, you'll see the two bright stars
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Polax and Castor, which represent the northern
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constellation of Gemini the twins. In Greek mythology, they
00:18:39
were brothers who travelled with Jason aboard the ship Argo in
00:18:43
search of the Golden Fleece. Polax is an orange-hued evolved
00:18:46
giant star, located 34 light-years away.
00:18:50
It has about twice the Sun's mass and has bloated out to
00:18:53
around 11 times the Sun's diameter. In 2006, an extrasolar
00:18:58
planet or exoplanet, designated Polarx B, was discovered
00:19:02
orbiting the star. The planet is a gas giant, orbiting its host
00:19:06
star every 1.61 Earth years. The other star, Castor, is located
00:19:11
some 51 light years away.
00:19:13
It's actually a system of six stars comprising three eclipsing
00:19:16
binaries. Eclipsing binaries are binary star systems in which the
00:19:20
orbital plane of the two stars in the system lies so nearly
00:19:24
along the line of sight from the observer here on Earth that the
00:19:27
stars appear to eclipse each other.
00:19:29
Looking to the northeast now, and you'll see the star Regulus,
00:19:32
or Little King, the brightest star in the constellation LEO
00:19:35
the Lion. LEO is mentioned by Homer in his famous 8th century
00:19:39
BC poem, The Odyssey.
00:19:42
According to Greek mythology, LEO was killed by Hercules as
00:19:45
the first of his twelve labours. Located some 79 light years
00:19:49
away, Regulus is a multiple star system, composed of at least
00:19:53
four stars.
00:19:54
Regulus A, designated Alpha Leonis, is a spectroscopic
00:19:58
binary comprising a rapidly spinning spectral type B
00:20:01
blue-white star around 3.5 times more massive than the Sun, with
00:20:05
some 288 times the Sun's luminosity, and a small
00:20:09
companion star, most likely a white dwarf, the stellar corpse
00:20:13
of what once would have been a Sun-Like star.
00:20:16
The pair take about 40 days to orbit each other. Spectroscopic
00:20:20
binaries are double star systems orbiting each other so closely
00:20:23
and at such an angle that they can only be visually separated,
00:20:26
from our viewpoint here on Earth at least, by their spectroscopic
00:20:29
signatures.
00:20:31
Astronomers describe stars in terms of spectral types. It's a
00:20:35
classification system based on temperature and characteristics.
00:20:38
The hottest, most massive and most luminous stars are known as
00:20:42
Spectral Type O blue stars. They're followed by Spectral
00:20:45
Type B blue-white stars, then Spectral Type A white stars,
00:20:49
Spectral Type F, Then there's whiteish yellow stars, then
00:20:52
spectral type G yellow stars, that's where our Sun fits in.
00:20:56
Then there's spectral type K orange stars, and the coolest
00:20:59
and least massive of all stars are spectral type M red stars,
00:21:03
commonly referred to as red dwarfs. Each spectral
00:21:06
classification system is further subdivided using a numeric digit
00:21:10
to represent temperature, with 0 being the hottest and 9 the
00:21:13
coolest.
00:21:14
And then you add a Roman numeral to represent luminosity. So, our
00:21:19
Sun technically is a G2V or G2-5 yellow dwarf star. Also included
00:21:25
in the stellar classification system are spectral types LT and
00:21:29
Y, which are assigned to failed stars known as brown dwarfs,
00:21:33
some of which were born as spectral type M red dwarf stars
00:21:36
but became brown dwarfs after losing some of their mass.
00:21:39
Brown dwarfs fit into a unique category between the largest
00:21:42
planets, which can have around 13 times the mass of Jupiter,
00:21:45
and the smallest spectrotype M red dwarf stars, which are
00:21:49
around 75 to 80 times the mass of Jupiter, or about 0.08 solar
00:21:54
masses.
00:21:55
The primary star in Alpha Leonis completes a full rotation around
00:21:59
its axis in under 16 hours. That 's incredibly quick, especially
00:22:03
when compared to our Sun's 30-day rotational period. Now
00:22:07
this gives the primary star an oblate appearance, and it causes
00:22:10
what's known as gravity darkening, meaning its poles are
00:22:13
considerably hotter and five times brighter per unit surface
00:22:16
area than its equatorial region.
00:22:18
Scientists estimate that if it were rotating just 15% faster,
00:22:22
the star's gravity would be insufficient to hold it
00:22:25
together, and it would literally spin itself apart.
00:22:28
Located further away are Regulus B, C and D, which are all dim
00:22:33
main sequence stars. Main sequence stars are those
00:22:36
undergoing hydrogen fusion into helium in their core, like the
00:22:40
Sun's currently doing. Regulus B and C are thought to orbit each
00:22:44
other every 600 Earth years and are located around 5
00:22:48
astronomical units away from Regulus A.
00:22:51
An astronomical unit is the average distance between the
00:22:53
Earth and the Sun, around 150 million kilometres, or 8.3 light
00:22:58
minutes. Regulus B is a spectrotype F white-yellow star,
00:23:02
while its companion, Regulus C, is a small spectrotype M
00:23:06
red-dwarf star. Regulus D is a bit more of a question Mark. It
00:23:10
's a dim star.
00:23:11
And, at least from our point of view, it appears to be sharing
00:23:13
motion across the Sky with other members in the group. At the
00:23:17
opposite end of the constellation of Regulus is the
00:23:20
star Beta Leonis, or Denebola, the horse's tail. It's a
00:23:24
luminous white star thought to be spectra type A, about half as
00:23:27
bright as Regulus, and the third brightest star in the
00:23:30
constellation LEO.
00:23:32
Beta Leonis has about 1.8 times the mass of the Sun and about 15
00:23:36
times the Sun's luminosity. It's suspected of being a dwarf
00:23:40
Cepheid or Dita Scuti type variable star, meaning its
00:23:43
luminosity varies very slightly over a period of several hours
00:23:46
due to pulsations on its surface.
00:23:49
Also at the other end of LEO are the stars Theta and Lota Leonis,
00:23:53
the loins of the lion. Theta Leonis is about 165 light years
00:23:57
away. It's a very young spectra type A white star, about two and
00:24:02
a half times the mass of the Sun. With an age of just 550
00:24:06
million years, Theta Leonis spectra shows enhanced
00:24:09
absorption lines for metals, that is elements other than
00:24:12
hydrogen and helium.
00:24:14
This increased metallicity appears around 12% higher than
00:24:17
the Sun, allowing the star to radiate with some 141 times the
00:24:21
luminosity of the Sun from its outer atmosphere, at an
00:24:23
effective temperature of 9350 Kelvin.
00:24:26
Literally giving it a white-hot glow. Located some 79
00:24:30
light-years away, Lothar Leonis is another spectroscopic binary,
00:24:34
consisting of two stars orbiting each other every 183 Earth
00:24:38
years. The primary star is the spectrotype F yellow dwarf star,
00:24:42
a little hotter and more massive than the Sun.
00:24:45
Algebra, or Gamma Leonis, is a binary star system with a
00:24:48
visible third component. The two primary stars are located 126
00:24:53
light-years away and can be resolved in a backyard
00:24:55
telescope. Both are yellow giants, orbiting each other
00:24:59
every 600 Earth days.
00:25:01
The unrelated tertiary star, named 40 Leonis, is a yellow
00:25:05
tinned star which can be seen through binoculars. Its
00:25:08
traditional name, Algebra, means the forehead. Other stars in the
00:25:12
system include Delta Leonis or Zosma, which is a blue-white
00:25:15
star 58 light-years from Earth, Epsilon Leonis, a yellow giant
00:25:19
some 251 light-years from Earth, and Zeta Leonis, an optical
00:25:22
triple star.
00:25:23
The brightest component is a white giant about 260 light
00:25:27
years from Earth, while the second brightest star, 39
00:25:29
Leonis, is widely spaced and is located to the south of the
00:25:33
primary, with the third and faintest star in the system, 35
00:25:36
Leonis, located to the north.
00:25:39
Also located in LEO is Tau Leonis, visible as a double star
00:25:43
through binoculars. It includes a yellow giant located some 621
00:25:47
light years from Earth and a binary secondary star, 54
00:25:50
Leonis. ...a pair of blue-white stars divisible in small
00:25:53
telescopes and located 289 light-years from Earth.
00:25:58
Also in the constellation LEO, you'll find the LEO Triplet, a
00:26:01
group of three galaxies, Messier 65, Messier 66 and NGC 3628, all
00:26:08
appearing relatively close together. Messier 65, also known
00:26:12
as NGC 3623, is an intermediate spiral, possibly barred spiral
00:26:17
galaxy, about 37 million light-years away.
00:26:21
M65 disk appears to be slightly warped. And a relatively recent
00:26:26
burst of star formation is suggestive of some gravitational
00:26:29
interaction with the other two galaxies in the LEO Triplet,
00:26:32
possibly around 800 million years ago.
00:26:34
Nearby is Messier 66 or NGC 3627, another intermediate
00:26:40
spiral galaxy, some 95 light-years wide and about 36
00:26:44
million light-years away.
00:26:46
Gravitational interaction from its past encounters with the
00:26:49
neighbouring galaxies in the triplet has resulted in
00:26:51
extremely high central mass concentration, a high
00:26:55
molecular-to-atomic-mass ratio, and a resolved non-rotating
00:26:58
clump of neutral atomic hydrogen apparently removed from one of
00:27:01
its spiral arms.
00:27:03
The third member in the group is NGC 3628, the Hamburger Galaxy,
00:27:08
a spiral galaxy with a spectacular 300
00:27:11
light-year-long tidal trail of gas and stars.
00:27:15
NGC 3628 is located 35 million light years away. Its most
00:27:20
conspicuous feature is the broad and obscuring band of dust
00:27:24
located along the outer edge of its spiral arms, effectively
00:27:27
transecting the galaxy to the view from Earth.
00:27:31
Other bright well-known galaxies in LEO include Messier 95,
00:27:35
Messier 96, Messier 105 and NGC 2903. M95 and M96 are both
00:27:44
spiral galaxies, each about 20 million light-years from Earth.
00:27:48
M95 is a barred spiral. Another barred spiral galaxy is NGC2903,
00:27:55
which is thought to be very similar in size and structure to
00:27:58
our own Milky Way galaxy. It was discovered by William Herschel
00:28:03
in 1784. Close to the M95-M96 pair is the elliptical galaxy
00:28:09
M105, which is also around 20 million light years from Earth.
00:28:14
Okay, let's turn to the east now and the constellation of Corvus
00:28:17
The Crow. In Greek mythology, Corvus was a really clever crow,
00:28:21
in fact he could talk to people. However, after refusing to speak
00:28:25
to the god Apollo, he was banished to the Sky, together
00:28:28
with Crater the Cup and Hydra the Snake. One of the brightest
00:28:32
stars in Hydra is Alphard the Solitary One, so named because
00:28:36
it appears all alone in the Sky.
00:28:39
Okay, turning to the western horizon now, and you'll see the
00:28:42
star Achenar in the southern tip of the constellation Eridanus
00:28:45
The River. Eridanus is one of the largest and longest
00:28:48
constellations in the Sky. Achenar means the river's end,
00:28:52
as it marks the end of the river Eridanus. Located around 139
00:28:57
light-years away, Achenar is a binary star system, comprising
00:29:00
two stars Alpha Eridni A and Alpha Eridni B.
00:29:04
One of the ten apparent brightest stars in the night
00:29:06
Sky, Alpha Rydeni A is a young, hot spectro-type B blue star,
00:29:11
about 6.7 times the mass of the Sun, with a stunning 3 times
00:29:16
the Sun's luminosity. Akhenar's extremely high rotational
00:29:20
velocity of over 16 km per second gives it an oblate shape,
00:29:24
making it one of the least spherical stars in the Milky
00:29:26
Way, with an equatorial diameter some 56% greater than its polar
00:29:30
diameter.
00:29:31
This distorted shape means the star displays significant
00:29:34
latitudinal temperature variations, with its polar
00:29:37
temperature being above 20 Kelvin, while its equatorial
00:29:40
temperature, being much further away from the stellar core, is
00:29:43
only around 10 Kelvin.
00:29:46
Those high polar temperatures are generating a fast polar
00:29:49
wind, ejecting matter from the star and generating a polar
00:29:52
envelope of hot gas and plasma. The companion star, Alpha Rydeni
00:29:56
b, appears to be a spectral type A white star with about twice
00:30:00
the mass of the Sun. The two stars orbit each other at an
00:30:03
average distance of roughly 12.3 astronomical units.
00:30:09
Now, just a quick reminder that March 14th marks the yearly
00:30:13
celebration of the mathematical constant, pi. Pi is the ratio of
00:30:17
a circle's circumference to its diameter. But it's also an
00:30:21
irrational number, meaning its decimal representation never
00:30:24
ends and never repeats. More than just a number, pi has
00:30:28
important applications in astrophysics, orbital mechanics
00:30:31
and other fields of astronomy.
00:30:33
It's been calculated to over a trillion digits. And the current
00:30:37
record for reciting pi from memory is over 70 digits.
00:30:41
Imagine sitting next to that person at a dinner party. As for
00:30:44
me, 359's about it. Of course, as well as Pi Day, March
00:30:50
14 is also the birthday of the great Professor Dr Albert
00:30:54
Einstein.
00:30:55
Science writer Jonathan Alley from Sky Telescope magazine
00:30:59
joins us now for the rest of our tour of the Marching Skies.
00:31:03
We'll start with the view to the south, which we normally do,
00:31:06
which is where we find plenty of bright stars. And constellations
00:31:09
to see this time of the year. First of all, of course, there's
00:31:12
the Southern Cross, which is quite easy to see at the moment.
00:31:15
It is lying on its left-hand side, so you've got to bear that
00:31:18
in mind when you go out to have a look at it. It's not standing
00:31:20
upright. It's on its left-hand side. And by cross, we mean it's
00:31:23
a crucifix state.
00:31:25
It's not like a plus symbol type cross. It's a crucifix state,
00:31:30
but it's lying on its left-hand side, down to the southeast,
00:31:32
about halfway up from the horizon. Now, don't confuse it
00:31:36
with the thing called the False Cross. Which is a
00:31:38
similar-looking group of stars in a cruciform shape, and which
00:31:43
at the moment is higher up and also lying on its left-hand
00:31:46
side. A lot of people do get these two star groups mixed up.
00:31:51
The easy way to tell them apart is that the Southern Cross is
00:31:53
smaller. Most people actually, they go out and they look for
00:31:55
the Southern Cross, and if they've got a fair idea of what
00:31:56
shape it is, they see the False Cross first because it's bigger,
00:32:01
and they think, oh, that's the Southern Cross. But down below
00:32:03
it is the real Southern Cross, and it's much smaller. If stars
00:32:06
are brighter...
00:32:08
But the cross-section itself is smaller, so that people tend to
00:32:11
not see it sometimes. It's a bit strange. Anyway, don't get
00:32:13
confused. If you're going out to look for the Southern Cross,
00:32:16
just bear in mind that there's another group of stars up there
00:32:18
that look the same shape, but a bit bigger. Now, just near to
00:32:22
the Southern Cross are the two bright stars known as the
00:32:24
pointers.
00:32:26
These are Alpha and Beta Centauri. Alpha Centauri is the
00:32:29
star system that's nearest to our solar system and is
00:32:32
comprised of three stars. One of them, a small star called
00:32:35
Proxima Centauri, is the actual closest of the three, but it's
00:32:39
far too dim to be seen unless you have a quite big telescope
00:32:43
and know exactly where you're looking.
00:32:45
The Alpha and Beta themselves are really nice and bright and
00:32:48
Alpha, as I said, is a three-star system. The closest
00:32:50
star, the tiny star, is far too dim to be seen. And even the
00:32:53
other two stars that make up... It just may look like it's just
00:32:56
one star to the naked eye.
00:32:58
There are lots of double stars up there and binary stars and
00:33:00
even triple star systems and more in the night Sky. But to
00:33:03
look at them just with the unedited eye, you wouldn't know.
00:33:06
You need to get telescope onto them and you can then start to
00:33:08
separate the two stars or three stars apart. So when you're
00:33:11
looking at Alpha, you're looking at two main stars.
00:33:16
You can see separated, even a small telescope is separated,
00:33:21
but the third one you won't see unless you get a really really
00:33:24
big telescope onto it and you know exactly where you're
00:33:27
looking. Now the Magellanic Cloud galaxies can also be seen
00:33:30
pretty much due south this month. These are two small
00:33:33
galaxies that are companion galaxies to our own Milky Way.
00:33:36
To the naked eye, they look like just fuzzy clouds, hence the
00:33:39
name. But we do need dark skies to see them, though. Where I am
00:33:43
in Big City, I struggle to see the Magellanic Clouds because
00:33:47
we've got so much light pollution around me. But if you
00:33:49
can get somewhere dark, you don't have to be out of the
00:33:51
country, just far enough away from a sporting field that
00:33:55
doesn't have it.
00:33:56
Lights on at night or something like that, or a park, or just
00:33:59
anywhere we can get away from some lights, or just block the
00:34:01
lights from view behind a building or something. And you
00:34:03
do need to let your eyes adapt to the dark, too.
00:34:05
This is a thing that people don't often realise when they're
00:34:08
starting out, is that you're going outside from being inside,
00:34:11
and the light's bright in their house. You do need at least 20
00:34:14
minutes, 30 minutes preferably, to let your eyes get adjusted to
00:34:18
the dark, and again, keep away from street lights and things,
00:34:21
because that's just going to ruin it again. Really fine
00:34:23
protector might need them.
00:34:25
And don't use a flashlight unless it's got a red filter on
00:34:27
it.
00:34:28
Yeah, red filter is a good thing to do. You can get some red
00:34:31
cellophane. Red cellophane's not the best thing to use, but if
00:34:33
that's all you've got, that's fine. You can get special red
00:34:35
filters to put over flashlights or torches. There are certain
00:34:39
wavelengths that are better than others.
00:34:40
In fact, people have tested all sorts of colours to see whether
00:34:42
they're better than red even, but red's a good bit to use. So
00:34:46
if you do need to go out and find your way around in the
00:34:49
dark, Yes, he's a Torch or a flashlight. He's got a red Torch
00:34:52
on him. Now, the Milky Way, which is our galaxy, it's just
00:34:55
our galaxy from the inside, basically.
00:34:57
It can be seen stretching from the southeast to the northwest.
00:35:00
And as you go north along the Milky Way, heading away from the
00:35:03
Southern Cross, you go through some really good constellations,
00:35:06
some of which most people would never have heard of.
00:35:08
One such as Zela and Puppet, Canis Major, Orion. Orion's one
00:35:13
that people might have heard of. Canis Major, you've got the star
00:35:15
Sirius. It's the brightest star in that constellation. And it is
00:35:18
actually the brightest star in the night Sky as seen from
00:35:21
Earth. So you really can't miss Sirius, it's nice and bright.
00:35:26
Orion, the constellation of the hunter, it's dominated at each
00:35:30
end by bright stars. At one end you've got Rhyza, on the other
00:35:33
end you've got Betelgeuse, as it probably should be pronounced.
00:35:36
And through its middle, perpendicular, runs a belt of
00:35:39
three stars. That's the hunter's belt from which dangles his
00:35:43
sword.
00:35:44
So these three stars in a straight row are very easy to
00:35:46
see. And also within Orion, you've got the famous Orion
00:35:50
Nebula. Now through its telescope, the Orion Nebula
00:35:52
looks... Really, really good. But the naked eye is just a
00:35:54
fuzzy patch. And again, you need dark area and eyes that have
00:35:57
adapted to the dark. But it's really good, even if you don't
00:36:00
have access to the telescope.
00:36:01
If you look up a picture of the Orion Nebula on the internet or
00:36:03
something and see what it looks like, and then you go outside at
00:36:06
night, and okay, all you're seeing is a little fuzzy little
00:36:08
patch.
00:36:08
But when you think, wow, I'm actually seeing that, and that's
00:36:10
what that fantastic picture is that I saw on my screen, and I
00:36:14
can actually see it, even if it 's just a fuzzy patch, I can
00:36:16
actually see it with my own eyes, and it's 1 light years
00:36:19
away, roughly. And it's just... The most amazing, it's really
00:36:22
amazing when you see something in a book or a magazine or on
00:36:24
the internet and you think, I wonder if I can see that.
00:36:27
You can go out and you can. It won't look as good, of course,
00:36:30
but you know that you are actually seeing something that's
00:36:33
hundreds or thousands or tens of thousands of light years away.
00:36:36
That's part of the fun of doing stargazing. Now, what else have
00:36:39
we got? Low down on the western horizon, sort of after sunset,
00:36:42
you've got a wedge of stars.
00:36:44
There's a reddish-coloured star at one corner. This is the head
00:36:48
of the constellation Taurus, and that reddish star is called
00:36:52
Aldebaran. The eastern half of the Sky in the evening during
00:36:55
Mars is pretty bare, really, but later in the night, after the
00:36:58
Earth has turned a bit on its axis and some more stars have
00:37:00
come up in the east, we've got the constellation Virgo.
00:37:03
Now, Virgo's a very big constellation, covers a lot of
00:37:05
the Sky, and it, too, to the naked eye, looks a bit bare. But
00:37:09
amateur astronomers just absolutely love it. Because
00:37:12
within Virgo is a huge cluster of galaxies, all sorts of
00:37:16
galaxies spread over the constellation.
00:37:18
Big ones, small ones, ones with an edge going, ones with a face
00:37:21
on, different kinds, and backyard telescopes can reveal
00:37:24
dozens and dozens and dozens of these. So amateur astronomers
00:37:27
really love this time of year, getting on towards wintertime in
00:37:30
the Southern Hemisphere and summertime in the Northern
00:37:32
Hemisphere, because Virgo's up and therefore you've got lots of
00:37:35
galaxies.
00:37:35
Now, turning to the planets, what have we got? We've got
00:37:37
Jupiter. Jupiter is big and bright in the northwest after
00:37:40
sunset. You really can't miss it. It's about a third of the
00:37:42
way up from the horizon.
00:37:44
If you are struggling to work out which one of those things up
00:37:47
there is Jupiter, that's big and bright, but go out on the 14th
00:37:50
and look for the moon because the nearest bright end of the
00:37:53
moon will be the planet Jupiter. To see Mars, you have to be up
00:37:58
before dawn, I'm afraid, so you've got to be an early riser
00:38:00
or getting to bed late. Look to the east after about 5 a.m. And
00:38:05
see if you can spot it.
00:38:05
It looks like a medium brightness, reddish, orangey
00:38:09
coloured star. Although it's not a star, of course, it's planet
00:38:12
Mars. But that's what it looks like. It just looks like a
00:38:15
little orangey red dot. But that 's planet Mars with all those
00:38:19
rovers and things roving around it and that helicopter that used
00:38:23
to be flying around. I think it 's me.
00:38:25
It's done a staff now hasn't it, the helicopter, it broke one of
00:38:28
its... Yeah, but what an amazing thing though, it just lasted so
00:38:33
fucking long, which most of these things do on Mars, they
00:38:36
tend to last a long, long time.
00:38:39
That's Mars, now about half an hour after Mars rises, the same
00:38:42
part of the Sky, Venus will rise above the eastern horizon, and
00:38:47
look, you cannot miss Venus, you cannot mistake it for anything
00:38:51
else, because it's the biggest, brightest thing. In the night
00:38:54
Sky other than the Sun and the Moon.
00:38:56
So you'll see this whopping huge bright-looking star, in inverted
00:39:01
commas, but it's actually the planet Venus. And about half an
00:39:05
hour after Venus rises, there's another planet, which will be
00:39:07
Saturn. Saturn will be rising over the eastern horizon,
00:39:11
although in the first half of the month, it'll be sort of
00:39:14
beginning of the dawn light, so it'll be a bit hard to see.
00:39:16
Wait until the second half of the month, and in particular, go
00:39:18
out and take a look on the 22nd. Really, if you've got good
00:39:21
weather, get up early, before dawn, go out in the 22nd,
00:39:24
because you'll see that Venus and Saturn have moved very, very
00:39:28
close to each other. They'll only be about a third of a
00:39:30
degree apart.
00:39:31
That's really quite close. Now, of course, they're not actually
00:39:33
really close to each other out in space. It's just a line of
00:39:36
cyber effects from our point of view on Earth. They appear to be
00:39:39
in the same direction. Having them that close together, only a
00:39:41
third of a degree apart, is pretty great.
00:39:44
And they're both quite bright. Venus is very bright. Saturn is
00:39:48
probably half that bright. But these sort of things happen
00:39:54
several times during the year with different planets, but, you
00:39:56
know, it's worth getting out to have a look at any particular
00:39:59
one.
00:40:00
To get the chance because the next one might be clouded out or
00:40:02
whatever, or you might be sleeping or forget to wake up or
00:40:06
whatever. So 22nd of March, go out in the eastern part of the
00:40:10
Sky before dawn, and you should see big bright Venus, and right
00:40:15
next door, fairly bright Saturn. And that's the end of the Sky
00:40:18
for March.
00:40:19
That's Jonathan Nally from Sky And Telescope magazine. And this
00:40:23
is Space Time.
00:40:40
And that's the show for now. Space Time is available every
00:40:44
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to spacetimewithstuartgary.com for full details.
00:41:34
And if you want more SpaceTime, please check out our blog, where
00:41:37
you'll find all the stuff we couldn't fit in the show. As
00:41:39
well as heaps of images, news stories, loads of videos, and
00:41:43
things on the web I find interesting or amusing. Just go
00:41:46
to spacetimewithstuartgary.Tumblr.-
00:41:49
com.
00:41:50
That's all one word, and that's Tumblr without the E. You can
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also follow us through at Stuart Gary on Twitter, at SpaceTime
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with Stuart Gary on Instagram, through our SpaceTime YouTube
00:42:01
channel, and on Facebook, just go to Facebook.com forward slash
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SpaceTime with Stuart Gary.
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You've been listening to SpaceTime with Stuart Gary. This
00:42:11
has been another quality podcast production from Vite.Com.