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Emily LakdawallaAugust 12, 2011

Comet Garradd in 3D (sort of)

Amateur astronomer Patrick Wiggins sent me this neat little animation of comet Garradd moving against background stars through an hour's worth of observing. I'm not any kind of astronomer but if I were I think I would get a kick out of looking at things that appear to move within one night of watching -- asteroids, comets, Jupiter's spots. I'm impatient that way.

Comet Garradd

Patrick Wiggins

Comet Garradd
A series of 10 exposures taken 6 minutes apart on August 9 show fuzzy comet Garradd's position shifting against background stars. Paramount ME, C-14 operating at f/5.5, ST-10XME, binned 2x2, clear filter, 60 second exposures taken 6 minutes apart on 9 August between 0734 and 0838 UT. FOV is about 18' x 26'.

Patrick reminded that you can turn animations like this into 3D images. I took sequential frames from the animation above and turned them into a red-blue anaglyph animation, where the comet pops forward out of the image:

Comet Garradd in 3D (sort of)

Patrick Wiggins

Comet Garradd in 3D (sort of)
Sequential images of comet Garradd were combined as anaglyphs to make this red-blue 3D animation. The 3D effect arises from the comet's motion, not from any instantaneously observed parallax in the comet's position.

There is a 3D effect, and it is true that the comet is (a lot) closer to us than the background stars, but the 3D effect has nothing to do with the instantaneous physical position of the comet with respect to the stars.  When we see the world in 3D, it's because of parallax.  Our eyes occupy two different positions, so when we look at objects against a background, the object appears in a different position with respect to the background in our two eyes.  

The 3D effect here isn't due to instantaneous parallax like that which we see with our own eyes; the parallax arises from the motion of the comet through time.  Or maybe it arises from the motion of Earth changing our point of view on the comet.  Or maybe it's a bit of both. Everything's in motion!

Thinking about this further, I realized that if an observation like this managed to catch two moving objects in the same field of view, the faster-moving object would appear to be closer to your eyes than the slower-moving object.  So there's an observing challenge for you amateur astronomers -- someone send me an animation containing two moving things in the same field!

Read more: pretty pictures, 3D, animation, amateur astrophotos, comets, optical telescopes

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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