Supernovae are the violent explosions of stars occurring at the end of
their lives. On average, one supernova goes off every 50 years or so in
our Galaxy. The enormous explosion from these stars blasts material out
into the surroundings at very high speeds, sweeping up the surrounding
gas into a giant bubble. This is known as a supernova remnant. The
shell (or bubble) shines at many different wavelengths, and is very
bright in the X-ray because the material from the explosion is very
hot. Different things are happening in different wavelengths; when we
observe in, say the X-ray, we are looking at the parts of the shell
that are much hotter than the areas shining in the visible.
Supernovae release more energy in a single instant than the Sun will
produce in its whole lifetime! If the nearest massive star, Betelgeuse,
in the constellation Orion, were to go supernova it would (for a short
time) be brighter than the full moon. Here we will look at observing these ancient explosions and making color images.
If you don’t have an observing session, you can search through our archive for images of the supernova remnant Cassiopeia A.
If you do have an observing session, you can choose to observe any one of the ancient supernovae below. Make sure you observe the supernova remnant in three different filters and that you have around 3 - 4 observations in each filter. Exposure times per filter are listed in the table below.
| Name |
B (s)
|
V (s)
|
R(s)
|
Halpha |
Oiii
|
RA
(h:m:s) |
Dec
(d:m:s) |
|
Cas A
|
200 - 250
|
150 - 20 |
150 - 200
|
150 - 200
|
150 - 200 |
23:23:26 |
+58:48:00 |
|
| Kepler |
300 - 350 |
250 - 300
|
250 - 300
|
250 - 300 |
250 - 300
|
17:30:42
|
-21:29:00 |
|
| N49 |
400 - 450
|
450 - 500
|
450 - 500 |
500
|
450 - 500
|
05:26:01 |
-66:05:06 |
|
The coordinates are given in Right Ascension and Declination.
Right Ascension is given in hours, minutes and seconds and is the
equivalent of longitude on Earth. 00h is the equivalent of the
Greenwich meridian, and the 360° full circle of the sky is split into
24 hours. The RA coordinate therefore determines the position of the
object with respect to the 00h line. Declination is the 'up and down' angle of the object in the sky compared to the equator. A negative value is below the equator (southern hemisphere) and a positive value is above it (northern hemisphere). Declination is measured in degrees, arcminutes and arcseconds. There are 60 arcseconds in an arcminute and 60 arcminutes in a degree.
Stacking your images
Once you have downloaded your FITS files from the telescope, you will need to stack the multiple images for each filter together. This needs to be done as the total visible light from ancient supernovae is actually quite faint over a large area. Stacking effectively ‘adds’ together your individual images to make a final image. To stack your images you need to use the software package IRIS (see the How-to article).
Many colors
Now you have your data, you can go to the next step which is making color images from your stacked filters. Use the How-to make color images with photoshop article to do this and you will have a fantastic image of an ancient explosion. Watch this space for more advanced activities you can do with your color image...
