Asteroid Question

[Fallingstar1971]

Has anyone seen or heard of anyone who has taken a photograph of Jupiter with an asteroid eclipsing it from the main belt?

Star

 

[neilsox]

A total eclipse could not occur, so perhaps transit is better than eclipse. Several billion tiny asteroids can likely cause such a transit. If Jupiter is 400,000 kilometers from the sun, the thousand kilometer asteroid is 350,000 kilometers from the sun, the asteroid would be visable as a dark dot on the face of Jupiter with a telescope. There might also be a dark shadow less than 100 kilometers wide. I'm not sure of the math: perhaps closer than 50,000 miles is necessary to cast a dark shadow, but closer would not be considered a main belt asteroid. Some NEO = near earth orbit asteroids transit Jupiter, and the dot could totally block the view of Jupiter for a few seconds. The probable event (all cases) is predictable, so there are likely pictures. Partial eclipses occur daily, but Jupiter is only dimmed by a few parts per million. A CCD = charge coupled devise telescope at max contrast can likely record these events, but CCD can also produce fake eclipses = artifacts at maximum contrast. Please correct me if I am wrong. Neil

 

[MeteorWayne]

Yes, transit would be the proper term.All asteroids would be far too small, with the possible exception of Pallas, Vesta, and maybe Hygiea.

 

[Fallingstar1971]

Yes transit is what I meant......I was just curious, I have never seen or heard mention in the media.

Star

 

[yevaud]

Ceres as well.

 

[MeteorWayne]

Technically, Ceres is not an asteroid, but a dwarf planet. that's why I specifically did not include it! :lol:

 

[yevaud]

Ah, Ceres will always remain the Mother of all Asteroids to me.

 

[kg]

Here is a link to a website about observing occultations.
http://www.eclipsetours.com/occultationc.html
There is a link in there to a occultation prediction site. I took a quick look and didn't see any planets listed.

I think the occultation of a bright star by an asteroid is a rare event and difficult to predict. The occultation of a planet by an asteroid would be much rarer still and maybe alot harder to predict seeing that the planet is moving as well? I have a feeling that such an event would not go unoticed! The closest encounter with Jupiter that I can think of the comet Shoemaker-Levy 9 but I can't recall seeing any pictures of any of the fragments transiting Jupiter.
http://en.wikipedia.org/wiki/Shoemaker-Levy_9

 

[MeteorWayne]

Actually, asteroid occultations of stars in not difficult to predict if the asteroid orbit is known well. In fact, the International Occultation Timing Association:

http://lunar-occultations.com/iota/iotandx.htm

makes predictions months in advance. Some of the most accurate size and shape estimates of astroids result from these precise observations.

When an asteroid occults a star (which is of course a point light source) the asteroid causes the star to wink out as the asteroid passes in front. Hence the timing can be very precise.

A planetary occultation would be much harder to see, since the planet is not a point source, but a disk, and the asteroid would cover only a tiny portion of the disk. This would cause only a VERY tiny drop in the brightness of the planet, with no precisely defined start and end times, particularly if the planet has an atmosphere. The resultant dimming would probably be too small to measure amont the "noise" in the planetary brightness itself as it passes through the roiling atmosphere of earth.

 

[MeteorWayne]

Just for context, here are predicted occultations of stars by asteroids:

http://www.asteroidoccultation.com/IndexAll.htm

Here's the list for January 2010, there are more than 260:


http://www.asteroidoccultation.com/2010_01_si.htm

Wayne

 

[neilsox]

Hi Wayne: I looked at the list all link. All the stars occulated seem to be between mag 6.0 and 13. 6, so there would be lots more mag 13.6 to mag 18. but I suppose only a few telescopes are capable of mag 18 at less than one second exposure time. Short exposure is necessary to time the occultation plus or minus 0.1 seconds. I suppose asteroids with dimensions of less than one kilometer produce occulations lasting less than 0.1 seconds, unless observed from a fast flying airplane. Has this been attempted?
The incomplete dimming suggests that the star disc is larger in nanoseconds of arc than the apparent asteroid disc, but I suppose there is a different explanation?
Apparently the occulations are visable only very close to the straight line on the map of Earth. Some vague something tells me some of those straight lines should be slightly curved. Occulation of binary stars less than one second of arc apart should be interesting. Is there a good reason why stars brighter than mag 6 occulations are not listed? Neil

 

[MeteorWayne]

The incomplete dimming suggests that the star disc is larger in nanoseconds of arc than the apparent asteroid disc, but I suppose there is a different explanation?

To be honest, I'm not sure. Will need to do some research on that.

Apparently the occulations are visable only very close to the straight line on the map of Earth. Some vague something tells me some of those straight lines should be slightly curved. Occulation of binary stars less than one second of arc apart should be interesting. Is there a good reason why stars brighter than mag 6 occulations are not listed? Neil

Well they are not really straight lines, even if they look so. The actual line is a combination of the movement of the earth in it's orbit, the rotation of the earth, and the motion of the asteroid. For such small objects, the predicted path is just a rough approximation, as with so many things in astronomy, the only way to know if an occultation occurs at your location is to get out there and look!

As for why there are no 6 mag or brighter star occultations listed, it is simply that there are far fewer of those stars that will line up with an asteroid. There are only a half dozen to a dozen or so of such events in an average year.

It's like meteors. For every 1st magnitude sporadic meteor, there will be 2000 6th magnitude ones...which can't be observed in most populated areas because there is too much light pollution... :geek:

 

[neilsox]

Thank you for confirming some of my speculation. It is comforting to learn that reading between the lines sometimes produces correct conclusions. Neil