1.2 Save images in FITS format
This short video clip talks you through the process of retrieving your COAST images and saving them to FITS format. Detailed instructions are given in the activity that follows.
Download this video clip.Video player: video_fits.mp4
Transcript
INSTRUCTOR:
OK. So here I am logged into telescope.org, ready to retrieve some of my variable star images for using the aperture photometry. And the first thing I'm going to do is to go to the Your Requests page. And here I've got a list of all the images that I've requested, the various objects. I've got some requests for EA2 and EA1. Those images haven't been taken yet, so they've just been listed as waiting.
But further down, I've got some images of variable star EA3 from our list. Those are shown as complete, so those are ready for me to go ahead and collect. I've got a number of these because I've been bracketing my exposures. I'm going to go ahead and choose this one. Click on that, it'll take me to the view page. There's not an awful lot to see at the moment, but I'm going to fix that up in a moment.
First of all, I'm going to go to the Data tab, just to confirm that this is the image I wanted. So I can check on this tab, I can check the exposure. 30 seconds. That's right. That's one of my bracketed exposures. And the green filter. So that is indeed the image that I wanted.
And so I can then go across to the Edit tab. And this time my image is loading here, and the software is going to adjust the contrast and the brightness so that we can see what's going on. I've got a nice image here, with plenty of stars in the field of view. And I can even go ahead and adjust the contrast a little bit more to darken the background, make it very easy to see what's going on.
Now, I'm fairly confident in this image that this star here, close to the centre, is the variable star that I'm interested in. If I've entered my coordinates correctly and the telescope has gone to those coordinates, the target star should be at or very close to the centre of the frame, the centre of the field of view. And I can even zoom in a little bit using the zoom slider. I'm fairly confident this is the star that I'm interested in, but of course, we're going to use the Finder charts later on to absolutely confirm that that's the correct star.
For now, I'm going to go ahead and save my image. And when I do that, I'll be saving it in the FITS astronomical data format, which is a sort of raw data format. So it will save. It won't save any of the changes that we've made to brightness and contrast. It'll just save the raw data.
So to do that, I'll go ahead to the Save icon on the floppy disc. And this time I'm selecting FITS. Save file. And I've already got a location set up where I want to save all my coast images. So I'll just go ahead and save the image in there. And that's my image saved, ready for the next step, which will be the aperture photometry itself.
Interactive feature not available in single page view (see it in standard view).
Activity 1 Retrieve your COAST images in FITS format
Timing: Allow approximately 20 minutes
- Log in to your telescope.org account and go to the Your requests section of the website to select one of your variable star images. Remember, any images that have been taken will show as Complete. Any images that are still in the queue will be shown as Waiting – you will need to check back later to see if these have been completed.
- From the list, click on the first completed image that you want to work with. This takes you to the View tab.
- To confirm any details about the image, such as filter and exposure time, click on the Data tab. This lists some of the information from the FITS header. You may wish to make a note of these details, although they will also be in the header of the saved FITS file.
- Click on the Edit tab. You do not need to make any adjustments to the image, as the FITS format will store the raw data.
- To save your image, click on the floppy disk icon top right (E). Select fits and then Save File to save a copy of the image to your computer. Remember to keep a note of where you have saved it and the filename of the image.
- Repeat for each of the images that you want to save. If you have used exposure bracketing you should have four images with exposure times of 15, 30, 60 and 120 seconds. Save all four.
Having saved all of your images as FITS files you will probably find that you cannot view them directly on your computer. FITS files are designed to work in specialised astronomical analysis software so don’t worry if your computer doesn’t recognise them.
In the next section you will learn how to use a web-based astronomical data processing tool to make the measurements that you need.