søndag 19. oktober 2014

Pluto - a "wandering star"

I know that Pluto is no longer defined as a planet, but for most of my life, Pluto captured my imagination as a planet. So far out. So cold. I remember seeing artists' impressions of what it would be like to stand on the surface. Looking back at the bright star 5 billion km away. But I have never been able to see it with my eyes. Only in pictures. It moves slowly across the sky. Barely visible to the eye in a large amateur telescope. But with a short exposure, it is possible to spot. Not in itself, but by the very definition of the word planet. The word comes from Greek "Planetes aster", or "wandering star". The old Greeks didn't have telescopes, so to them, everything on the night sky, save from the Moon, where stars. And some of them moved. These are what we now know as planets. I decided a week ago to try to capture the movement of Pluto, the planet, on three days. To see it moving against the stars in the background.
The following image shows Pluto on November 11th. Try to find it! It is literally finding the "needle in the haystack".



And it is no wonder that nobody found it until 1937. First of all, it is very faint. Around magnitude 14 (which is more than 1000x fainter than the faintest star we can see with an unaided eye). But even when you use a long exposure like above, it looks just like a star in the image. It is impossible to discern it from the stars. But if you compare images taken a few days apart, it becomes apparent. Clyde Tombaugh compared the images taken a few days apart using a blink comparator. One of the stars moved. Today, we can use a computer to create an animation, and suddenly, it stands out from the background.
I added three images, taken a few days apart, and it is obvious that one of the "stars" is moving. It is a "wandering star", "planetes aster". A planet. The planet Pluto. Click on the image to get a bigger version.


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