Podcaster: Richard Drumm
Title: Space Scoop: Distant Starlight Creates a False Dawn
Organization: Astrosphere New Media
Link : astrosphere.org ; http://unawe.org/kids/unawe1446/
Description: Space scoop, news for children.
Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
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Transcript:
This is 365 Days of Astronomy. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.
Today’s story is…
Distant Starlight Creates a False Dawn
Kids! Imagine your parents are driving you home from a night at your grandparents’ house. Traveling along a dark country lane you look out and see a hazy pyramid of light extending from the horizon up into the sky. It looks kinda like the Milky Way or light pollution from a nearby town, but your sense of direction’s good and you know for certain that there are no towns in that direction. It could be the Sun about to rise, but it’s only an hour since sunset and this light is in the West, where the Sun has just gone down.
So, what’s up with dat?
This eerie glow is called ‘false dawn’ when it’s near dawn or ‘zodiacal light’ for either dusk or dawn. It’s caused by sunlight reflecting off dark cosmic dust in the Solar System. These rocky grains are leftover from when the planets and moons formed nearly 5 billion years ago.
Now when we astronomers say “dust” we don’t mean anything like the dust under our beds, all cat hair & fabric fibers, no, no. This dust is made of tiny bits of carbon, silicon and such, the sorts of things you’d need to build a planet.
The dust grains here are 10 to 300 microns in size, similar to pollen grains. A bit larger than smoke particles, which can top out at about 1 or 2 microns. A micron is a millionth of a meter, just to refresh your memory. And so you don’t have to Google it…
It’s called zodiacal light because it runs along the ecliptic, the plane of our solar system, where the constellations of the zodiac are located. It’s brighter when you see it closer to the Sun, but it does extend all the way through the night sky from dusk to dawn.
The part of this band of light that is exactly opposite the Sun is slightly brighter and is called the Gegenschein, which is German for countershine. Light pollution in inhabited parts of the world has rendered the Gegenschein invisible these days. You’ll have to travel waaay out into the wilderness on a perfectly clear and moonless night to even have a chance of seeing it.
The artwork that accompanies today’s episode contains a zodiacal light image that is credited to the ESO and astrophotographer Yuri Beletsky. Yuri also took a spectacular image of the Gegenschein from the Paranal Observatory in Chile.
By combining the power of four very large telescopes at Paranal into one super-telescope, an international team of ESO astronomers has given themselves the ability to peer reeeealy closely at 92 relatively nearby stars. And they discovered a ghostly zodiacal light glowing around nine of them – exactly as we see it in our Solar System!
The glow around these distant stars is caused by starlight bouncing off cosmic dust. And just like here, this dust is made up of broken asteroid bits and left over comet tails. Now, while this light may be a beautiful and exciting discovery, it’s not all good news.
You see, searching for planets around other stars is a very difficult task. These alien worlds are so far away that they appear incredibly small and dim. This makes it almost impossible to photograph them.
In fact, out of almost 2,000 planets that have been discovered around distant stars, only around 20 have actually been photographed! The rest have all been discovered using clever tricks, such as the radial velocity method where the planet tugs on the parent star and makes it move a tiny bit closer to us, and then farther away.
As the star moves farther away and then closer it’s spectrum is red shifted and then blue shifted ever so slightly. This shift can be studied to determine the mass of the planet and to tell if there are more than one of them.
Like bright headlights on a dark road, the glare of this extrasolar false dawn will make it even more difficult to spot any Earth-like planets that lie within far away Solar Systems.
Here’s a Cool Fact
The zodiacal light spotted around these 9 stars is 1,000 times brighter than the one seen in our own night sky! So if you were on a planet there it’d be much easier for you to see than our own zodiacal light, which is so dim it basically disappears when the Moon’s out or a city is nearby.
End of podcast:
365 Days of Astronomy
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The 365 Days of Astronomy Podcast is produced by Astrosphere New Media. Audio post-production by Richard Drumm. Bandwidth donated by libsyn.com and wizzard media. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. In the new year the 365 Days of Astronomy project will be something different than before….Until then…goodbye