Starship Asterisk*

Close Encounter with M44

Explanation: On Monday, January 26, well-tracked asteroid 2004 BL86 made its closest approach, a mere 1.2 million kilometers from our fair planet. That's about 3.1 times the Earth-Moon distance or 4 light-seconds away. Moving quickly through Earth's night sky, it left this streak in a 40 minute long exposure on January 27 made from Piemonte, Italy. The remarkably pretty field of view includes M44, also known as the Beehive or Praesepe star cluster in Cancer. Of course, its close encounter with M44 is only an apparent one, with the cluster nearly along the same line-of-sight to the near-earth asteroid. The actual distance between star cluster and asteroid is around 600 light-years. Still, the close approach to planet Earth allowed detailed radar imaging from NASA's Deep Space Network antenna at Goldstone, California and revealed the asteroid to have its own moon.

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I'm trying to figure out the patterns in the asteroid trail... it's not clear if this is a single exposure or multiple. why does the track wiggle around like it does? (magnify it to see what I mean)

TomMunnecke wrote:I'm trying to figure out the patterns in the asteroid trail... it's not clear if this is a single exposure or multiple. why does the track wiggle around like it does? (magnify it to see what I mean)

More information would be useful. Here is my educated guess. The image was made with a single-shot color camera, and consists of four 10-minute exposures. It is possible that some of the brightness variation is caused by rotation of the asteroid, but I suspect most is related to the conversion of the raw Bayer-filtered image to color and to seeing variations. The wiggling is tracking error- a combination of periodic and non-periodic error in the mount drive system and mechanical vibrations and resonances in the mount and telescope. It's always present in astronomical images made from the ground, but seldom apparent because all it does is slightly increases the size of stars. But with a moving object, you can see it clearly.

Don't you suppose some of the variation could be caused by atmospheric turbulence?

geckzilla wrote:Don't you suppose some of the variation could be caused by atmospheric turbulence?

Yes. That's what "seeing variations" are. I think more of that shows in the intensity than in the wiggle, but I'm sure it's present in both.

Normally I'd look at the FWHM of the stars to get an estimate of the seeing quality. Can't reliably do that from a JPEG image, but it looks to be around 5 pixels. The plate scale is 3.2 arcsec/pixel. This large FWHM points to tracking error more than seeing error.

Chris Peterson wrote:

geckzilla wrote:Don't you suppose some of the variation could be caused by atmospheric turbulence?

Yes. That's what "seeing variations" are.

Missed that section of sentence reading your first post.

Great!!

Comets and asteroids and moons......oh my!!!

:---[===] *

This is a fine color picture of M44. The Beehive is characterized by a lot of apparent double stars (well, they would have to be incredibly wide doubles). Also the colors are nice. The brightest stars of the Beehive are of spectral class K (yellower than the Sun) and A (bluer than the Sun). This picture brings the colors out nicely.

Of course the presence of the asteroid doesn't hurt, either!

Ann

A lovely image. And I'm impressed with the accuracy of the tracking. I suppose I could only hope to match such apparent accuracy by adding noise.

Rather more interesting than "asteroid-flies not-very-close-to-star-cluster" is that 2004 BL86 has a moon.
http://www.jpl.nasa.gov/news/news.php?feature=4459
The Goldstone Observatory used radar to image the 70meter moon as the asteroid made its 1.2M Kilometer flyby of Earth.
An observing tour-de-force!

John

JohnD wrote:Rather more interesting than "asteroid-flies not-very-close-to-star-cluster" is that 2004 BL86 has a moon.
http://www.jpl.nasa.gov/news/news.php?feature=4459
The Goldstone Observatory used radar to image the 70meter moon as the asteroid made its 1.2M Kilometer flyby of Earth.
An observing tour-de-force!

John

From the movie I would not myself be able to tell that the "moon" was not simply a background star, with the asteroid moving as fast as it is. Are they sure?

henrystar wrote:From the movie I would not myself be able to tell that the "moon" was not simply a background star, with the asteroid moving as fast as it is. Are they sure?

It's a radar image. There are no background stars, only nearby objects that are reflective in the radio spectrum.

Oh my, it has its own "moonlet". Great APOD today.

Chris Peterson wrote:

TomMunnecke wrote:I'm trying to figure out the patterns in the asteroid trail... it's not clear if this is a single exposure or multiple. why does the track wiggle around like it does? (magnify it to see what I mean)

More information would be useful. Here is my educated guess. The image was made with a single-shot color camera, and consists of four 10-minute exposures. It is possible that some of the brightness variation is caused by rotation of the asteroid, but I suspect most is related to the conversion of the raw Bayer-filtered image to color and to seeing variations. The wiggling is tracking error- a combination of periodic and non-periodic error in the mount drive system and mechanical vibrations and resonances in the mount and telescope. It's always present in astronomical images made from the ground, but seldom apparent because all it does is slightly increases the size of stars. But with a moving object, you can see it clearly.

Chris P. knows his imagery! Thanks, Your explanations on how these images are created are a real help to us in the "point and shoot" crowd.

LocalColor wrote:Oh my, it has its own "moonlet". Great APOD today.

Has anyone seen any discussion on how M44's encounter with the Earth/Moon system may have perturbed the orbit of the "moonlet" ?

FloridaMike wrote:Has anyone seen any discussion on how M44's encounter with the Earth/Moon system may have perturbed the orbit of the "moonlet" ?

I expect any effect was very small. The moonlet is only a couple hundred meters from the asteroid, and pair were over a million kilometers from the Earth. Tidal acceleration varies as the inverse cube of distance. Effectively, whatever gravitational forces the pair experienced (and are experiencing) from the Earth-Moon system were uniform across them, so there would be no perturbation.

Chris Peterson wrote:

henrystar wrote:From the movie I would not myself be able to tell that the "moon" was not simply a background star, with the asteroid moving as fast as it is. Are they sure?

It's a radar image. There are no background stars, only nearby objects that are reflective in the radio spectrum.

BTW, check out this conversation. He called it light! https://twitter.com/michael_w_busch/sta ... 5617952772

geckzilla wrote:BTW, check out this conversation. He called it light! https://twitter.com/michael_w_busch/sta ... 5617952772

Woo hoo! :)

Really great imaging to capture the moon [moonlet]. I assume they had no idea it was there prior to the radar images coming back. It would have been great to see an entire orbit. It appears that the orbit is pretty close to the "plane of passage", but maybe about 15 degrees off. Earth must have bent this pair's path as they went by. I'l take Chris' word for it that their mutual dance would not be noticeably altered, though.

Chris Peterson wrote:

henrystar wrote:From the movie I would not myself be able to tell that the "moon" was not simply a background star, with the asteroid moving as fast as it is. Are they sure?

It's a radar image. There are no background stars, only nearby objects that are reflective in the radio spectrum.

Thanks!

Chris Peterson wrote:

FloridaMike wrote:Has anyone seen any discussion on how M44's encounter with the Earth/Moon system may have perturbed the orbit of the "moonlet" ?

I expect any effect was very small. The moonlet is only a couple hundred meters from the asteroid, and pair were over a million kilometers from the Earth. Tidal acceleration varies as the inverse cube of distance. Effectively, whatever gravitational forces the pair experienced (and are experiencing) from the Earth-Moon system were uniform across them, so there would be no perturbation.

Nitpick: it was asteroid 2004 BL₈₆ which came close to the Earth-Moon system, not open star cluster M44 (thankfully).

Nitpicker wrote:Nitpick: it was asteroid 2004 BL₈₆ which came close to the Earth-Moon system, not open star cluster M44 (thankfully).

Indeed. But that would have been [briefly] exciting.

Chris Peterson wrote:

geckzilla wrote:BTW, check out this conversation. He called it light! https://twitter.com/michael_w_busch/sta ... 5617952772

Woo hoo!

He must be the exception that proves the rule about radio astronomers not referring to what they study as "light".

Chris Peterson wrote:

Nitpicker wrote:Nitpick: it was asteroid 2004 BL₈₆ which came close to the Earth-Moon system, not open star cluster M44 (thankfully).

Indeed. But that would have been [briefly] exciting.

Yeah, I've always been easy to please. The asteroid was exciting enough for me.

I would also like to mention that this image includes fake diffraction spikes.