Thursday, October 02, 2008

The False-Color Moons Of Filipe Alves


Normally colors in astronomy are rare, transitory and subtle. They can be among the most beautiful things I’ve ever seen, but colors in astronomy typically are not intense.

One of the cool things about digital astrophotography, however, is that a skilled person can tweak, manipulate and push reality and create colors that are amazing.

Filipe Alves takes careful photographs of the Moon through filters which allow specific spectrum colors to pass, generally red and blue. Then he uses the brightness differences between the different spectrum results to create artificial color images of the Moon.

These images are not only beautiful, but they highlight different surface characteristics which makes it easier to become familiar with the lunar landscape.

Planetary geologist Charles Wood writes a monthly column for Sky & Telescope magazine about the Moon. In the September, 2008, issue, Wood points out that although these false-color images aren’t ‘real’ in the sense that we would never see these colors observing the Moon, the differences in brightness of the different spectrum images is caused by actual differences in the composition of the lunar surface. For instance, the strong contrast between the light Sea of Tranquility and the dark Sea of Serenity is caused by the lava which formed the Sea of Tranquility being rich in titanium. Although we would never see these particular colors observing the Moon by eye, on a good night with good equipment and a sharp eye, observers might be able to see some color differences between areas of the lunar surface.

To give you an idea of how subtle and transitory colors in astronomy typically are, Wood writes about his own experience looking for color on the Moon: “...I have only noticed colors in one spot: the low plateau northwest of the bright crater Aristarchus. For me the Aristarchus Plateau appears a distinct olive. Other observers have reported seeing it as yellowish or slightly red, perhaps like hot-dog mustard mixed with a little ketchup.

Given that green (‘olive’) and red are what artists call ‘opposite’ colors, the fact that experienced observes can report the same feature as either green or red tells you how variable the experience of colors in astronomy can be.

There is one tip I can pass along for trying to observe colors on the Moon. Normally lunar observers avoid the full Moon. The light is too bright and the absence of shadows makes it hard to distinguish lunar features. But the extra light from the bright full Moon can help activate color receptors in the eye. If you allow your eyes to adapt to the brightness of a full Moon, you can sometimes see colors you normally would miss. Be warned, however, that although observing the full Moon is safe, almost certainly you will get a headache as your eyes constantly try to adjust first to the darkness around you and then to the brightness of the Moon.

There is a second way, a less dramatic way, of tweaking, manipulating and pushing reality to create color images of the Moon. You can take careful, full-color photographs and use image-processing techniques to adjust the color saturation to maximum. Filipe Alves provides a reasonably detailed tutorial on how to do it here: How to capture the color of the Moon, by Filipe Alves











No comments: