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View Full Version : Star-Asteroid Occultation

MAPNUT
2010-Apr-06, 06:50 PM
I wonder why the comments to Phil's post today are turned off? I wanted to ask why the path of the occultation runs south to north, according to the map shown in the Sky & Telescope article: http://www.skyandtelescope.com/observing/home/89690067.html
It will move a couple thousand miles north-northeast in about an hour. I'd expect that the asteroid is moving more-or-less parallel to the ecliptic, thus the "shadow" would move east-west or west-east (I can't figure out whether the orbiting of the asteroid or the rotation of the earth would govern). Is the northward movement just due to the tilt of the earth's axis?

Also it's interesting that they want to collect observations to delineate the shape of the asteroid's "shadow". How many would you need to be able to make an animation of the shadow moving across the planet's surface? I hope someone's planning to do that.

Hornblower
2010-Apr-06, 10:18 PM
I wonder why the comments to Phil's post today are turned off? I wanted to ask why the path of the occultation runs south to north, according to the map shown in the Sky & Telescope article: http://www.skyandtelescope.com/observing/home/89690067.html
It will move a couple thousand miles north-northeast in about an hour. I'd expect that the asteroid is moving more-or-less parallel to the ecliptic, thus the "shadow" would move east-west or west-east (I can't figure out whether the orbiting of the asteroid or the rotation of the earth would govern). Is the northward movement just due to the tilt of the earth's axis?

Also it's interesting that they want to collect observations to delineate the shape of the asteroid's "shadow". How many would you need to be able to make an animation of the shadow moving across the planet's surface? I hope someone's planning to do that.

We are close to the position at which Earth's orbital motion will cause the asteroid's apparent motion to shift from direct to retrograde. In the vicinity of this "stationary" point even a modest orbital inclination can introduce a proportionately large south-north component. The Earth's spin will contribute to this effect, slowing down any direct component and speeding up a retrograde component.

If we were in opposition with the asteroid, the ground track would be retrograde unless the asteroid was in an extremely eccentric orbit with perihelion near the Earth.

MAPNUT
2010-Apr-08, 03:45 PM
Ah, impending retrogradicity! Of course! Thanks, hornblower.