Lots of objects in the night sky are green, but they are green for a variety of different reasons.
Easy Being Green
Yes, comet Lovejoy is really green, and its all due to the molecules in its tail.
National Geographic Effect
You can see this effect in the image above. On the left is a Voyager II image of Jupiter’s great red spot as it appeared in NatGeo and elsewhere. On the right is the same image in its more true-color form. You can see why the colors were boosted. The true-color image lacks much of the depth and richness we like to see in images.
Cosmic Rainbow
Recently I wrote about the average color of the universe, as determined by a survey of more than 230,000 galaxies. While knowing the overall color of these galaxies is a fun little factoid, it isn’t particularly useful from a scientific standpoint. However the color was determined by the average spectrum of the galaxies, which is quite scientifically useful. This “cosmic rainbow” tells us about the history of star formation in the universe.
Cosmic Latte
At the turn of the 21st century, the Anglo-Australian Observatory made a large survey of galaxies in our universe, known as the 2-degree-field galaxy redshift survey (2dFGRS). It measured the spectra and redshifts of more than 230,000 galaxies. The main goal of the survey was to determine the distribution of galaxies within a radius of about 4 billion light years. A statistical analysis of this distribution could then be used to put constraints on things like dark matter and neutrino mass (which I’ll talk about another day).
True Blue
One of the cool things we’ve been able to do is determine an exoplanet’s color. The planet is known as HD189733b, and as seen in an article published in Astrophysical Journal Letters, it has a blue color. This does not mean this planet is Earth-like in any way. Neptune is also blue, and it is hardly a paradise world. I’ve written about this exoplanet before, where it was found that the hot Jupiter-type planet has atmospheric winds of over 6,000 miles per hour. We now know that its atmosphere contains silicates which give it a blue color. It seems its atmosphere is filled with small droplets of silica that scatter blue light, giving it a blue color.
Snapshot
Suppose an advanced alien race discovered our little planet. From their great telescopes they could tell our atmosphere is rich in oxygen and water vapor, which would indicate this was a planet inhabited by living organisms. They therefore decide to send a probe to study our curious blue world. With their advanced technology, this alien species can send a probe across the vast distance of space using a device they call the Maguffin drive. The Maguffin drive can transport the probe to Earth almost instantly, but because of the tremendous energy it requires the probe can only stay on Earth for one second.
Shades of Gray
Despite all the wonderful color images we have from the Hubble space telescope, there is no color camera on the Hubble. The main reason for this is scientific. When observing astronomical objects, you’d like to get as much light as you can from the object. You also want to get as wide a range of wavelengths as you can.
Color Kin
We generally think of asteroids as looking like gray rocks. While that’s true to our limited eyes, more sensitive instruments find they have a variety of colors. You can see an example of this in the image above of the asteroid Vesta. This false color image was made by observing Vesta at various wavelengths in the visible and infrared spectrum. It shows that Vesta has variations in color too subtle for us to see with our eyes.
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