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Astronomy with an online telescope

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Picture of Una Collins

Una Collins Post 1

12 Jan 2021, 19:26

queries on Coast images



I took some images some time ago but had to take time out of the course so am only getting back now with queries on the results.  I hope that isn’t too late for queries on them.

I would like to check regarding job J368193

The image of Pleiades only shows the principal stars on the left side of the cluster. Can this be fixed?

What settings could I use to show the cluster as a whole


I took an image of the orion nebula  J368195 but its situated over at the right of the frame. Is this to do with co-ordinates? Or exposure time?

I also took 2 images of the crab nebula, one using SHO filter and one using BVR  J368194 , J368191. Neither show any details of the nebula, just a small dot! even after using editing tools. What could do to be able to capture a decent image of the nebula,  one that could be enhanced with the editing tools?

Also can changes made to the image with the editing tool be saved within the personal library on as well as in downloaded image?    .

I have really enjoyed the course and the wonderful resources so far and am looking forward to getting back into it.

Many thanks


Picture of Alan Cayless

Alan Cayless Post 2 (unread) in reply to 1

13 Jan 2021, 17:05

Hi Una;

Thanks for asking about these and for including the image numbers, which have really helped to see what's going on.

It's great that you have had plenty of images back, and it frequently takes a couple of goes to get the settings exactly right, so don't worry if they don't come out quite the way you wanted first time.

As you've asked about several different objects, I'll answer each in turn.


Picture of Alan Cayless

Alan Cayless Post 3 (unread) in reply to 1

13 Jan 2021, 17:19 Edited by the author on 13 Jan 2021, 17:19

Pleiades M45

Your image J368193 is indeed of the Pleiades, but only shows a part of it.  The Pleiades is relatively close, at about 450 light-years from Earth - making it bright and also quite large on the sky.  With an apparent diameter of over one degree, the Pleiades is simply too big to fit into COAST's field of view, so you will only be able to image part of it at a time.  

Unlike a telescope with changeable eyepieces used for visual observations, COAST's magnification is fixed, so we can't change the field of view. But you might want to try with some other clusters, for instance M29.

The bright star on the right hand side of your image with three smaller stars in a triangle to the right of it is Alcyone, and the two stars near the left side are Atlas and Pleione.  You may want to try and match these up with the display in Stellarium - zoom in to a field of view of about two-thirds of a degree and see if you can match them up with your image.


Picture of Alan Cayless

Alan Cayless Post 4 (unread) in reply to 1

13 Jan 2021, 17:28

Orion nebula M42

Your image J368195 has the Orion nebula on the right hand side, so it's just a little off centre.  You are correct - this is just a case of fixing up the coordinates a little bit.  

The coordinates listed on the header are:  RA 05h 36m 19.20s and Dec -05° 22' 39.80".  These are just a little bit away from the actual 5h 35m 24s and -5° 27' 0", and this has moved the nebula to the edge of the frame.  It's well exposed though, so you are on the right lines and worth requesting another.

What you could try here is to request the image by name rather than entering the coordinates.  In the Select Target box, try entering "M42" or "Orion Nebula" and it will pick up the entry from the catalogue.  That should give you a more centred image.


Picture of Alan Cayless

Alan Cayless Post 5 (unread) in reply to 1

13 Jan 2021, 17:35 Edited by the author on 13 Jan 2021, 17:35

Crab nebula M1

The Crab nebula is quite a faint object and so needs a long exposure.  Both your images   J368194 and J368191 have an exposure of 30 seconds, which is a little short.  This is especially the case with the SHO filters - these are narrow-band filters which let through only a very narrow range of wavelengths, resulting in less light and needing a longer exposure.  

Try again with the longest possible exposure (180 seconds). To make sure the image is well centred, you might want again to try requesting the image by name ("M1" or "Crab nebula").   


Picture of Una Collins

Una Collins Post 6 (unread) in reply to 1

13 Jan 2021, 22:01

HI Alan

Thanks so much for the detailed replies regarding the images I took in Coast. Its so helpful and Ill look forward to taking more using the guidelines and suggestions that you have given, 

Kind regards



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