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Asteroid 2005 YU55 - something I just don't get!


lukebl
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Were the rotation speeds of Venus and/or Mercury determined by Earth-based Doppler radar? I vaguely recall something about getting radar returns off one of those planets.

Amateur radio operators, incidentally, get returns from the Moon with about 400-1000 Watts of transmit power. It can be used as a communications method, called "moonbounce" or Earth-Moon-Earth (EME).

You are very correct about EME, but it can be done with much lower powers. I have managed it with 80 Watts and 2 x 8 element antennas. But it was quite difficult, the station at the other had a seriously big setup. 1500+ Watts and 24 x 17 element antennas.

Radio Amateurs have also managed to bounce signals off Venus back in 2009.

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Can someone tell me whereabouts to look for YU55 from the ground, which constellation/s it will be passing by.
Retro, there is a thread somewhere with a link to a video showing the path through the different constellations. I'll try to find it

Here I think, by Steve/tetentere of this parish,

http://stargazerslounge.com/observing-widefield-special-events-comets/160918-asteroid-yu55.html#post2011807

but that vid shows it for southern England, - because the asteroid is so close to us there will be considerable parallax between Wiltshire and Retro up in Cleveland. Steve did not say what software he used to produce that vid so I dunno how to adjust it for Retros site. However , it gives an indication of the approximate position for observers in the UK, more accurate info for the NE of England will need Cartes du Ciel and a good updated asteroids file :)

Dont blink or yu'll mis it :)

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This asteroid will be closer to Earth than what the moon is so why won't Earths Gravitation pull it in to us? Is it just to small?
It is very small but it has a high velocity, high kinetic energy, it will be deflected slightly but not sufficiently to either enter orbit round the earth or to crash into us ( I think, fingers xxed :) )

Oh, err, and the earth alone cannot capture it, it needs a 3body effect and the moon is too far away (angular) at the time (amongst other things)

Edited by Ptarmigan
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It is very small but it has a high velocity, high kinetic energy, it will be deflected slightly but not sufficiently to either enter orbit round the earth or to crash into us ( I think, fingers xxed :) )

Oh, err, and the earth alone cannot capture it, it needs a 3body effect and the moon is too far away (angular) at the time (amongst other things)

Sounds Logical. Thanks

Mike

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Hi all. Going back to my original post, the consensus seems to be that the crescent appearance of YU55 when imaged by radar was due to the doppler effect resulting from the object's rotation, which meant that the 'approaching' side was at a different image density to the 'receding' side.

However, the latest movie footage from NASA (here) indicates the the asteroid is rotating with its pole pointing straight at us. Surely, then, the doppler effect caused by the object's rotation would be negated, yet the object still apears as a crescent? Great bit of footage.

Edited by lukebl
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They pinged it with microwaves at an unusual frequency in order to pick it out from the background. Thereafter it was imaged by radiation whose original source was the sun - hence the crescent.

It's only 400m wide and revolves once every 20 hours. Could that produce doppler? Doubt it.

Well that's my ill-informed guess.

Incidentally if the earth was the size of a basketball this asteroid would be a 0.01 mm wide !

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They pinged it with microwaves at an unusual frequency in order to pick it out from the background. Thereafter it was imaged by radiation whose original source was the sun - hence the crescent.

It's only 400m wide and revolves once every 20 hours. Could that produce doppler? Doubt it.

Well that's my ill-informed guess.

Incidentally if the earth was the size of a basketball this asteroid would be a 0.01 mm wide !

Sounds plausible.

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Ok, I've done a little more reading!

I wasn't quite right before... doppler-shift radar imaging is a technique used to increase the resolution of the synthetic aperture. The doppler shift actually is plotted horizontally (the rotation causes this doppler shift, and so tells the receiver exactly where the signal bounced from along the axis perpendicular to the rotation). [previously I thought the doppler shift was plotted vertically]

Then, the delay of the returned signal is plotted vertically. The delay is caused by the distance of the asteroid from the transmitter/receiver. A signal hitting the centre of the asteroid returns sooner because it is closer. The only problem is, we can't know if a longer delay comes from the "top" or the "bottom" of the asteroid. Therefore the top and bottom are effectively plotted over the top of each other - looking like a crescent!

This is my understanding from what I've read...

[here is a blog article describing the technique]

Edited by Shibby
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