APOD: Close Encounter with M44 (2015 Jan 29)

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APOD: Close Encounter with M44 (2015 Jan 29)

Post by APOD Robot » Thu Jan 29, 2015 5:06 am

Image 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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TomMunnecke

Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by TomMunnecke » Thu Jan 29, 2015 5:14 am

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)

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Chris Peterson » Thu Jan 29, 2015 5:34 am

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

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by geckzilla » Thu Jan 29, 2015 5:38 am

Don't you suppose some of the variation could be caused by atmospheric turbulence?
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Chris Peterson » Thu Jan 29, 2015 6:09 am

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

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by geckzilla » Thu Jan 29, 2015 6:21 am

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.
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Boomer12k » Thu Jan 29, 2015 6:22 am

Great!!

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

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Ann » Thu Jan 29, 2015 6:59 am

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! :D

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Nitpicker » Thu Jan 29, 2015 7:03 am

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. :ssmile:

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by JohnD » Thu Jan 29, 2015 10:12 am

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

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by henrystar » Thu Jan 29, 2015 2:25 pm

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?

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Chris Peterson » Thu Jan 29, 2015 2:55 pm

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.
Chris

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by LocalColor » Thu Jan 29, 2015 4:18 pm

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

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by FloridaMike » Thu Jan 29, 2015 4:26 pm

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.
Certainty is an emotion. So follow your spindle neurons.

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by FloridaMike » Thu Jan 29, 2015 4:30 pm

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" ?
Certainty is an emotion. So follow your spindle neurons.

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Chris Peterson » Thu Jan 29, 2015 5:12 pm

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

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by geckzilla » Thu Jan 29, 2015 5:53 pm

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
Just call me "geck" because "zilla" is like a last name.

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Chris Peterson » Thu Jan 29, 2015 6:39 pm

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

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by MarkBour » Thu Jan 29, 2015 7:29 pm

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.
Mark Goldfain

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by hoohaw » Thu Jan 29, 2015 11:15 pm

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!

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Nitpicker » Thu Jan 29, 2015 11:56 pm

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).

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Chris Peterson » Fri Jan 30, 2015 12:06 am

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

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by BDanielMayfield » Fri Jan 30, 2015 12:10 am

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".
Just as zero is not equal to infinity, everything coming from nothing is illogical.

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by Nitpicker » Fri Jan 30, 2015 12:34 am

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. :ssmile:

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Re: APOD: Close Encounter with M44 (2015 Jan 29)

Post by starsurfer » Fri Jan 30, 2015 1:07 pm

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