Identifying Photographic Objects

This brief article was first published in Prime Focus Magazine, July 2020 edition.

Identifying Photographic Objects

Astro-imaging has revolutionised amateur astronomy over the last couple of decades. It’s now commonplace to see images which are equal or better than images taken by larger professional telescopes pre-digital photography.

With low noise CMOS and CCD cameras, amateurs are picking out fainter objects than are found in most sky atlases, making identification difficult.

It’s nice to independently confirm details of the target; and it’s enriching to identify any unexpected objects in the image.

Tools

These are some of the tools I use:

I submit all images to nova.astrometry.net (1). Within minutes I obtain a copy of my image, annotated with the identities of stars and certain deep sky objects. Useful stats are supplied, including the field of view and image orientation.

Sky Safari Pro (2) is an app for tablets and phones, surpassed by none, identifying over 100 million stars, 3 million galaxies down to 18th magnitude and every comet and asteroid ever discovered. It can do much more; but it’s the reliable object data base and display which are invaluable, at home and out in the field.

The Simbad online data base (3) is a library of deep sky objects maintained by Strasbourg Astronomical Data Centre. It’s updated by professional astronomers and is useful for teasing out more information about specific objects.

Another online tool which has come in handy has been Google Sky (4). It’s great for identifying sky coordinates of unknown objects.

Examples

Example 1: I recently posted a 2½ hour exposure of galaxy M83 on my website. It showed a pair of tiny smudges appearing next to M83. (see red marks on image). “What do I think they are?” enquired one subscriber, an experienced amateur astronomer. (Thanks, Marty).

M83 Galaxy NGC 5236 Stack of 49frames 8762 seconds exposure showing two remote galaxies indicated by superimposed tick marks
2020-06-19 M83 Galaxy NGC 5236 Stack_49frames_8762s
Image © Roger Powell

Using the above tools, I established the names of the mystery objects, both galaxies: ESO 444-85 and [R84] A1-342. I was astonished to learn that these 16th and 17th magnitude galaxies on my image are a boggling 665 million light-years away, (redshift 0.012 – receding at 4.6% light speed).

As an amateur, I never expected to capture galaxies that are two thirds of a billion light years away. The light was emitted when the first fossils that might represent animals were forming on Earth!

Example 2: I wanted to identify a fairly bright star close to globular cluster C105. I went to Google Sky for the coordinates and found the star – no longer bright but very faint. A variable star!

I was able to identify it as RZ Muscae, a star which pulses between 13th and 16th magnitudes every 47 weeks.

Astronomy is exciting but can be even more rewarding when you research and document what you capture!

Reference Links.

(1) http://nova.astrometry.net/upload
(2) https://skysafariastronomy.com/
(3) http://simbad.u-strasbg.fr/simbad/
(4) https://www.google.com.au/sky/

Prime Focus Magazine – June 2020
The Journal of Macarthur Astronomical Society, Australia
I’m a founding member of MAS.
🙃


8 Comments

    1. I’ve been using it for a few years. I usually link to the result in my image posts. It sometimes fails but normally functions it well. Glad you were able to try it yourself.

      The surprise for me was realising that something like Google Sky could actually be a useful tool in the identification process.

      Liked by 2 people

  1. That’s so cool that these resources exist for astro-photographers! I often wonder what I might be glimpsing when I stargaze with binoculars. Next time I’m curious about objects I can’t identify, I’ll check out Google Sky to see if that sheds some light on things!

    Liked by 1 person

    1. I hope it helps but don’t expect too much from Google Sky. It’s nice to scan around but otherwise rather basic.

      I found it a helpful stepping stone for determining the very accurate coordinates (shown bottom left) of some very faint objects in my long exposures. Then I could enter them in Simbad to get identification and details.

      For general stargazing with binoculars there are a number of better free options, maybe you’ve already discovered some. For a PC, Stellarium or Cartes du Ciel are good. For a tablet, Sky Safari is the best. For a phone there are also plenty of options available but whilst I have installed Sky Safari on my phone, I find the screen on my phone to be too small to be much value – but many might find it handy.

      Liked by 1 person

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