The Selu Observatory
How many people reading this are aware of the observatory at Selu? For those who aren’t, Radford does, in fact, have an observatory at the barn in Selu that is outfitted with a telescope made for taking pictures of different celestial objects. You can find the telescope in the silo, along with the computer with the program on it for finding different celestial objects. The program is called SkyX and, if you know what you’re looking for, you can mostly find whatever celestial object is in the sky at the time!
The Observational Astronomy class uses this observatory for their assignments and takes various pictures of whatever celestial object they need. (Just recently, we had to take a picture of a couple of different celestial objects. I had gotten some lovely pictures of the Andromeda Galaxy, which is our neighboring galaxy, from this outing! Though I ended up staying out past midnight, which was… less than ideal. Oops.)
However, taking pictures at the observatory isn’t as simple as just snapping a shot. So many factors go into getting that perfect picture of whatever you are looking for. Checking the times certain objects are out, using the right filters, and hoping the telescope works with us for the night are all factors in getting the shots you want amongst many others. Another one of these factors, and this is the one I will go into further, are things we call bias frames and dark frames.
The Bias and Dark Behind Your Favorite Pictures
When you look at official pictures of planets and stars, those images have been edited in one way or another. Sometimes it is by adding color or by just making the image clearer. The people making the images aren’t being deceitful; we are just limited by our location in the universe and our tools.
One of these edits is the removal of ‘noise’ in the pictures. Noise comes in many different variants and forms. The two specific versions we are looking at are the ‘read-out’ noise and the ‘dark current’ noise since those are the noises we take bias and dark frames to fix.
All cameras have read-out noise, also known as bias, even the one you might use at home! (Jones & Practical Astrophotography). One way to limit read-out noise is by getting a better camera (Wright). However, bias frames also help us get rid of the bias by identifying it! Bias frames are simple to take. You just take a couple of pictures with the camera at the shortest time possible with it completely dark (Practical Astrophotography). Viola! You now have a couple of bias frames.
Dark frames are a similar concept, except with a different noise. Dark current noise, also known as thermal noise, comes from the heat of the camera (Jones & Wright). Just like read-out noise, thermal noise is a part of the camera. You could take care of the noise by cooling off the camera (Wright). However, you can also take care of the dark current noise by using dark frames. They take longer than bias frames but are also done by having it completely dark. You want to take the pictures at the same temperature, and for the same length as the actual images you take, so that the thermal noise will be the same (Practical Astrophotography). Now you have your dark frames!
With both bias and dark frames taken, the rest is simple! Well, as simple as coding can be. You just need to use a coding software to subtract both the bias and the dark from your images. After that, you have some lovely pictures of whatever object in our sky you want!
Citations:
Jones, Trevor. “How to Take Bias Frames for Astrophotography”. AstroBackyard, https://astrobackyard.com/bias-frames-astrophotography/.
“A Brief Guide to Calibration Frames: Bias, Dark, Flats and Dark Flats”. Practical Astrophotography, 28 June 2015, https://practicalastrophotography.com/a-brief-guide-to-calibration-frames/.
Wright, Richard Jr. “An Astrophotographer’s Gentle Introduction To Noise”. Sky & Telescope: The Essential Guide to Astronomy, American Astronomical Society, 15 April 2018, https://www.skyandtelescope.com/astronomy-blogs/imaging-foundations-richard-wright/astrophotography-gentle-introduction-noise/.
Edited and Reviewed by Zoe Carter
