Opening up my Twitter feed this morning, I found the image above, posted by Mike Brown (yup, the same dude). It probably doesn’t look familiar to you, but that planet is Neptune.
I love Neptune. My love for the stormy blue planet is both aesthetic (who can resist that shade of blue in the classic Voyager 2 image?) and intellectual, since it is difficult enough to observe that there’s still a lot we don’t know about it. Neptune orbits about 30 times farther from the Sun than Earth does, and so not much sunlight reaches it; since we see planets by their reflected light, even on the darkest night far away from any city, Neptune isn’t visible without a telescope.
However, the Keck Observatory in Hawaii is not just a telescope: it’s two huge telescopes, each 10 meters (about 33 feet) in diameter. It also is able to observe in the infrared — the type of light we humans perceive as heat, and this is why Neptune looks so different in the image above. The colors are not what our eyes would see; they are a visual representation of the intensity of the light reflected, so brighter colors simply mean more photons entering the telescope. The bright orange and yellow colors are where infrared light reflected off of Neptune’s clouds, and the darker red indicates more light is being absorbed by methane in the atmosphere: fewer clouds in those regions.
The observation is at 1.5 microns of wavelength, or about 0.000059 inches. (Humans emit infrared light at about 9.5 microns, but the cloud-tops of Neptune are a lot colder than we are. Visible light wavelengths are between 0.7 and 0.9 microns.) The image above includes no light emitted directly by Neptune. This wavelength corresponds to high absorption from methane, which is why Brown selected it. His primary observational target on this run was Neptune’s moon Triton, which has a frozen surface containing, among other things, a lot of methane. The beautiful Neptune view is a nice bonus for the rest of us.
Neptune is a stormy place; its winds are phenomenally high, which is fairly typical for giant planets. Seeing the clouds directly in high contrast like this shows the banded structure and occasional hurricane-like storm. Observing in a different wavelength than we are accustomed to highlights different features; this is one of the glories of astronomy. We tend to think of visible light as the only type, since we rely so much on our eyes, but visible light is only one tiny part of a spectrum that ranges from high-energy gamma rays down to the low-intensity radio waves we rely on for communication. Every type of light reveals a different view of our wonderful universe; it’s telling how with each new way of seeing, astronomers discovered something new to see. Neptune is a calm blue in our eyes, but a raging turmoil of high winds when seen in infrared or radio.
The planet is named for the god of the ocean in Roman mythology, so I used the old Carter Family song as my title. Another song seems appropriate to end with: “It depends on what you look at, obviously/But it also depends on the way that you see.”
3 responses to “Storms Are On the Ocean”
I admit, I came for the Bruce Cockburn, but I stayed for the Neptune.
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