About observational astronomy: Difference between revisions

Revision as of 13:30, 8 February 2008

Astronomers can gain an understanding of objects in the universe by studying them with a telescope. Observational astronomy is the process of collecting and analyzing data to learn about these objects. In this learning project a computer program will be used to view and study images taken with a telescope to learn basic concepts in astronomy.

Activities

A CCD (Charge-coupled device) imaging system is a type of digital camera that is very sensitive to the dim light from distant objects. The CCD camera is attached to a telescope and the images are stored on a computer where they can later be analyzed. Astronomical images are stored in a computer file format called FITS. These images can be opened and viewed by using computer software that understands this file format.

Creating color images

Supernova

The Observational astronomy/Supernova page has images of galaxies where a supernova has been observed recently. In this activity we will retrieve images taken before the supernova occured, and compare them to the new images.

File:UGC14.jpg

Supernova 2006sr in the galaxy UGC 14 on 2007-01-02

Start Aladin and click on the Load... button. In the Server selector window click on DSS and select an image server. In the Target box enter the name of the galaxy which is UGC14 and then choose POSS1_Red for the Survey. Click Submit.

In the Aladin multiview window click on the icon labeled pixel. In the Pixel mapping popup window click on the Reverse button to change the image from a negative to a positive.

To find out when this image was taken click on the icon labeled prop and look for Date-Obs: which indicates that the image was taken Aug. 11, 1953.

Compare the image displayed in Aladin to the image shown at right. Click here (or on the image) to see a larger version and to find out when it was taken (the Date is 2007-01-02T23:03Z.) This supernova was first seen on Dec. 12, 2006, so it will not be visible in the earlier image displayed by Aladin. Do you see the supernova in the recent image? If you are unsure, click here to see another version of this image that is marked to show which star the supernova is.

More images of this supernova can be found in Category:Supernova Images or at the Supernova 2006sr in UGC 14 webpage. Compare images taken on different dates to see if the supernova has changed brightness. The difference will be very subtle in images taken a week apart. It is more obvious after about a month.

Readings

Background information:

References

Additional helpful readings include:

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 === Creating color images ===
-*Open another window in your web browser by clicking on this link to the [http://aladin.u-strasbg.fr/ Aladin Sky Atlas home page].
-There are three different versions of the Aladin program.  The version used in the first activity is the Aladin Previewer.  The Previewer is a convenient tool for browsing images but it does not allow for editing the images.  For this activity we will need to use the full version of Aladin.
-*To get started quickly just click on the [http://aladin.u-strasbg.fr/java/nph-aladin.pl Start Aladin applet] link to run Aladin in a browser window.  (You can also [http://aladin.u-strasbg.fr/java/nph-aladin.pl?frame=downloading Download Aladin on your machine] and run the program from your desktop.)
-*Start Aladin and click on the '''Load...''' button.  In the '''Server selector''' window click on '''DSS'''.  Pick a server to retrieve the images from, for instance '''DSS from STScI'''.  In the '''Target''' box enter '''M101''' and then choose '''POSS1 Red''' for the '''Survey'''.  Click '''Submit'''.
-The image of M101 will now download and open in the Aladin multiview window.  Notice that the image is displayed as a negative, ie. the bright stars appear black and the dark sky appears white.  This is an image taken through a red filter.  Next we will download a second image taken through a blue filter.
-*Go back to the '''Server selector''' window and choose '''POSS1 Blue''' for the '''Survey'''.  Click '''Submit'''.  You can now '''Close''' the '''Server selector''' window.
-We will now combine these two images to create a color composite.
-*In the Aladin multiview window click on the icon labeled '''rgb'''.  In the '''RGB image generator''' window use the pulldown menu to select the images for each color.  For '''Red''' choose the image name that includes '''POSS1_Red'''.  For '''Green''' leave it set to '''none'''.  For '''Blue''' choose the image name that begins '''POSS1_Blue'''.  Click on the '''Create''' button.
-A third image will now appear in the Aladin multiview window.  This type of image is called [[w:False-color|False-color]] because the colors do not exactly match what the human eye would see when looking through a telescope.
-*You can use the '''Zoom''' button below the thumbnail image to change the scale of the main image.  A zoom setting of '''1X''' will give you the largest image that can be displayed, without loss of resolution.  Clicking on the thumbnail will center that spot in the main window image.
 === Supernova ===

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