Starship Asterisk*

by **DavidLeodis** » Sat Jan 31, 2015 7:26 pm

Thanks for your help Nitpicker.

by **Nitpicker** » Sat Jan 31, 2015 12:47 pm

DavidLeodis wrote:The explanation states the image resulted from a 40 minutes exposure on January 27 (2015 by implication). In the image's Exif data that I was able to find it states "Date: January 27, 2015 2:40:14PM (timezone is 1 hour ahead of GMT)". On that date Italy was under Central European Time which is 1 hour ahead of GMT, so the image time will be the local time. Even allowing for 40 minutes exposure I cannot however see how it could have been dark enough to show the stars, etc. I am wondering therefore if the asteroid trail has simply been superimposed on a background image taken at other times. I apologise to the photographers if that is wrong but if so then the Exif data is very confusing (well it is to me ).

I have so often found confusing information in Exif data of APOD images that I am starting to think I'm wasting my time finding it as much of it seems so unreliable.

Hi David,

It would have been shortly before dawn in Italy, around 05:30 UTC on the 27th. I'd guess the exif data was from the time of processing.

by **DavidLeodis** » Sat Jan 31, 2015 11:58 am

The explanation states the image resulted from a 40 minutes exposure on January 27 (2015 by implication). In the image's Exif data that I was able to find it states "Date: January 27, 2015 2:40:14PM (timezone is 1 hour ahead of GMT)". On that date Italy was under Central European Time which is 1 hour ahead of GMT, so the image time will be the local time. Even allowing for 40 minutes exposure I cannot however see how it could have been dark enough to show the stars, etc. I am wondering therefore if the asteroid trail has simply been superimposed on a background image taken at other times. I apologise to the photographers if that is wrong but if so then the Exif data is very confusing (well it is to me

).

I have so often found confusing information in Exif data of APOD images that I am starting to think I'm wasting my time finding it as much of it seems so unreliable.

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

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

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.

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".

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.

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).

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!

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.

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! :)

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

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.

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" ?

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.

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

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

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.

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?

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

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.

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!

Ann

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

Great!!

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

:---[===] *

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.

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.

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

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

Starship Asterisk*

APOD: Close Encounter with M44 (2015 Jan 29)

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