APOD: Asteroid 2012 DA14 Passes the Earth (2013 Feb 17)

Comments and questions about the APOD on the main view screen.
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neufer
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Re: APOD: Asteroid 2012 DA14 Passes the Earth (2013 Feb 17)

Post by neufer » Thu Feb 21, 2013 3:36 pm

ta152h0 wrote:
There was a mention of a camera shake by one observer of the asteroid fly by. Is it possible to measure the distance of a background star by measuring the amplitude of the shake of a nearby object and compare the amplitute of the shake on a far away object and just bdo the math ? Couldn't be that simple , could it ?
This is called parallax and it generally involves the "shaking" of the Earth from side to side during its orbit around the sun.

Thankfully, the camera wasn't shaking quite that violently.
Art Neuendorffer

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Chris Peterson
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Re: APOD: Asteroid 2012 DA14 Passes the Earth (2013 Feb 17)

Post by Chris Peterson » Thu Feb 21, 2013 3:38 pm

ta152h0 wrote:There was a mention of a camera shake by one observer of the asteroid fly by. Is it possible to measure the distance of a background star by measuring the amplitude of the shake of a nearby object and compare the amplitute of the shake on a far away object and just bdo the math ? Couldn't be that simple , could it ?
No, it couldn't be that simple. The amplitude of motion will be instrumentally identical for all the objects, since they are effectively point sources at infinity. Of course, if you were close enough to the foreground object, it might appear to have a different amplitude than the stars, but every star would seem to be the the same distance... infinity.

In essence, we do use "camera shake" to figure out how far away nearer stars are. We can measure parallax, but we "shake" the camera by imaging at diametrical points in Earth's orbit. In essence, we shake the camera with a 2 AU amplitude.
Chris

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Re: APOD: Asteroid 2012 DA14 Passes the Earth (2013 Feb 17)

Post by rstevenson » Thu Feb 21, 2013 7:59 pm

ta152h0 wrote:There was a mention of a camera shake by one observer of the asteroid fly by. Is it possible to measure the distance of a background star by measuring the amplitude of the shake of a nearby object and compare the amplitute of the shake on a far away object and just bdo the math ? Couldn't be that simple , could it ?
The baseline you get from camera shake isn't quite big enough. :shock:

In order to measure distances to stars using parallax, we use a baseline "shake" of about 300,000,000 km. In other words, using a ground-based telescope we take a picture of a part of the sky, then wait six months for the Earth to "shake" over to the other side of its orbit, from where we take a picture of the same piece of sky. When we compare the two pictures we can see that nearer stars have moved against the essentially unmoving background stars. This technique allows us to measure distances to relatively nearby stars, less than 100 light years away. Wikipedia says...
Space astrometry for parallax

In 1989, the satellite Hipparcos was launched primarily for obtaining parallaxes and proper motions of nearby stars, increasing the reach of the method tenfold. Even so, Hipparcos is only able to measure parallax angles for stars up to about 1,600 light-years away, a little more than one percent of the diameter of the Milky Way Galaxy. The European Space Agency's Gaia mission, due to launch in 2013, will be able to measure parallax angles to an accuracy of 10 microarcseconds, thus mapping nearby stars (and potentially planets) up to a distance of tens of thousands of light-years from earth.
Rob

[And now, using 20/20 parallax, I can see that both Art and Chris have already answered the question. Yeah, but my answer has a longer baseline.]