Today's EPOD (2/1/2020)shows a group of Geminid meteors https://epod.usra.edu/blog/2020/02/enco ... tugal.html
They seem to radiate from more than one focus. Is this an artefact of a prolonged exposure? Or what?
John
Focus for meteors
-
- Tea Time, Guv! Cheerio!
- Posts: 1593
- Joined: Wed Feb 16, 2005 2:11 pm
- Location: Lancaster, England
-
- Abominable Snowman
- Posts: 18623
- Joined: Wed Jan 31, 2007 11:13 pm
- Location: Guffey, Colorado, USA
Re: Focus for meteors
You always have to be careful when projecting lines on any wide angle shot, due to the sort of distortions caused by projecting the sky onto a plane. However, in this case, consider that the image is a composite collected over four hours. In that time, the Geminid radiant moved from an altitude of 80° in the east (close to the zenith) to an altitude of 48° in the west- crossing nearly 50° of sky. So it's hardly surprising that the captured meteors appear unrelated.JohnD wrote: ↑Sat Feb 01, 2020 11:26 am Today's EPOD (2/1/2020)shows a group of Geminid meteors https://epod.usra.edu/blog/2020/02/enco ... tugal.html
They seem to radiate from more than one focus. Is this an artefact of a prolonged exposure? Or what?
John
Images which show a strong radiant are either taken during very active showers over a short period, or taken with a camera that is tracking the sky, and then composited onto a single background image.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com
*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com
-
- Tea Time, Guv! Cheerio!
- Posts: 1593
- Joined: Wed Feb 16, 2005 2:11 pm
- Location: Lancaster, England
Re: Focus for meteors
Thank you, Chris! I can see that, except that if the sky "moved" during the exposure, then the stars would appear as trails. Meteors are bright, so stars won't register in a tracking shot?
John
John
-
- Abominable Snowman
- Posts: 18623
- Joined: Wed Jan 31, 2007 11:13 pm
- Location: Guffey, Colorado, USA
Re: Focus for meteors
I don't know the finer details of how the image was processed. The meteors may have been masked out of the individual frames (which might typically be on the order of 30-second exposures). The stars we see here may have been from just one frame, or a longer frame. Obviously, when we're dealing with any image made over hours, where some things are moving and some things are not, where there is a range of brightness of many orders of magnitude, creative choices have to be made.
Chris
*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com
*****************************************
Chris L Peterson
Cloudbait Observatory
https://www.cloudbait.com