Talk:General Astronomy/Observational Astronomy

These are lecture notes I wrote for a course at the University of Phoenix. They are released to wikimedia under an appropriate creative commons license.

Roadrunner 20:58, 17 June 2006 (UTC) One problem with astronomy textbooks is that they don't mention how messy things really are. Everything is packaged in nice neat packets of information, and not much effort is spent describing the amount of effort it takes to get some real data. There is a lot of unglamourous grunt work that is involved in doing experiments, and that needs to be mentioned because most of astronomy doesn't consist of eureka moments, but rather a large amount of it consists of things that are tedious staring in front of a computer screen doing data reduction.

Getting data always starts with the instrument, and that usually means a telescope of some sort. You can think of a telescope as just a giant light bucket which is catching light particles from the sky and focusing them into a detector at the end of the telescope.

In ancient times (i.e. before 1980), what would be at the end of the telescope would be likely be a camera. The camera wouldn't use film but instead would record everything on a glass plate. Glass plates were needed instead of plastic because they stored better and didn't expand or contract as much over time.

Today, we are in a transition period between film cameras and digital cameras. However that transition happened in astronomy in the 1980's and many of the reasons that astronomers started using digital cameras are the same as the ones people are moving from film to digital cameras. The big one is that you can download the image onto your computer and then have the computer do image processing. This also means that you can store pictures, transmit them over the internet, and copy them to your friends. You can also instantly look at the picture and know if you took a picture of the right thing or if you need to reshoot the picture rather than waiting for the pictures to come back from the dark room. Finally, one other thing that is very important to astronomy is that digital cameras are far more sensitive to light than film cameras are. A film camera will catch about 5% of the light hitting it, while a CCD digital camera typically catches about 95% of the light which hits it. This isn't immediately obvious with a digital camera, but one thing that you can try if you have a digital camera is to take a picture at night, and you'll find out that it comes out much better than a film camera.

So when digital cameras first came out, plate photographs very quickly became obsolete, and most older observatories today have dark rooms and storage rooms for photochemicals, and these rooms are largely empty.

The digital chips which are at the end of most telescopes are largely the same as the ones in consumer digital cameras. There is one big difference in that the ones at the end of telescopes are generally cooled by liquid nitrogen. The reason for this is that a digital camera will pick up some noise from heat, and you want to reduce that noise as much as possible.

So you have a digital camera at the end of an instrument at the end of a telescope. Typically, in an observing run, you wake up at about 3 p.m. During the day the technicians will have installed the instruments that you need for a nights observing run. You go to the telescope at 3 p.m., check to see that everything is installed correctly, since you don't want to wake someone up at 3 a.m. if something breaks. You then spend the next two hours before sunset taking some calibration shots. One image set that you take involves closing the shutter, and taking an image of black. Even though the CCD chip is soaking in liquid nitrogen, there is still some noise in the picture that you want to get rid of. Another set of images you take, involves pointing the telescope at a spot on the wall which has been painted white. The reason for the white picture is that the different parts of the CCD chip will have different sensitivities. There are also cracks and dust and other noise on the CCD that you want to subtract from your observations. About this time, its dinner (or breakfast), so you head off and eat and come back when the sun starts setting.

After the sun starts setting, your first goal is to find the object that you are trying to photograph. You can punch in the coordinates into the computer, but that will only point the telescope in the general area of the sky that you are interested in. The next thing that you have to do is to take out your star atlas, and look for a pattern of stars that is close to the thing that you are looking for. This is a lot like driving in an strange city when you are looking at the monitor and then trying to match the patterns you see with the patterns on the chart.

So you've now found the object you are looking for. The next step is what has been called the world's slowest video game. The problem is that you want to keep the shutter open for a long time (say thirty minutes) to capture as much light from the object as possible. The trouble is that in that time, the sky moves. The telescope is trying to track the object, but the tracking isn't perfect. So you have to make adjustments to the telescope. What that involves is to mark the location of some stars on the television monitor with a grease pencil, and then if the stars start to drift, you use the control panel to move the stars back. The annoying thing is that you have to keep your eyes on the monitor. In between these measurements, you take some snapshots of a calibration device. If you are looking at spectra, you take picture of a flourscent lamp that has lines in certain known positions. If you are measuring brightness, then you need to take some pictures of a star whose brightness is known.

So after a night of all of this, you now have some data on hard disk, and you go to sleep. The next few weeks is where the hard part comes in. You see you have a lot of raw data, but it's not very useful to anyone. The problem is that none of the data has been calibrated. So you spend the next few weeks taking the data, subtracting the black leve, correcting the white levels, stretching and shrinking the picture so that you know what the frequencies of your spectra are. You might also be spending your time doing things like trying to correct for the effects of dust in the galaxy. Through it all, you are probably using an astronomy package called IRAF, which you like all big software packages has its cute bugs and idiosyncrasies.

After all of this, you now have tables and charts which the world is interested in. You then type up a paper, and then upload it to www.archvix.org and then send it off to a journal. The journal then takes the paper submits it to three anonymous referees who then evaluate the paper. In some cases, they will give the go ahead to publish. In very rare cases, they will say that the paper is beyond hope of publication. In most cases, they will return the paper with

After all of this, you now have tables and charts which the world is interested in. You then type up a paper, and then upload it to www.archvix.org and then send it off to a journal. The journal then takes the paper submits it to three anonymous referees who then evaluate the paper. In some cases, they will give the go ahead to publish. In very rare cases, they will say that the paper is beyond hope of publication. In most cases, they will return the paper with some comments, questions, and suggestions, and there is usually some back and forth before the paper is approved.

In the mean time, you are busy thinking up of experiments and observations you want to do next, and are spending your time reading up on what the latest data is, helping to design new instruments for your telescope, or working on proposals to get telescope time or grant money.

It's a very long slow process, and its full more of hard work than of eureka moments. But as things plod along, you get more and more data, and slowly it becomes more and more clear what is going on out there in the universe.

Polaris location
The text states that Polaris is on the "cup" of the Big Dipper (Ursa Major). This is incorrect- Polaris is at the end of the "handle" of the Little Dipper (Ursa Minor). May I correct this or can someone else do it please? That glaring mistake says a lot about the accuracy of the rest of the text. Perhaps the author meant to say that the cup of Ursa Major points to Polaris? That's how I learned to find it as a child, was by following a line from the cup of the big dipper.
 * Yes, you may correct it. That is the point of a Wiki. If you like, you can add a diagram as well. There are lots of images to choose from at Wikimedia Commons.  --Jomegat (discuss • contribs) 00:33, 1 December 2012 (UTC)

Aesthetic Bold - mid sentence
I was going through each chapter and removing the bold terms that are part of a sentence especially mid or end. However this is more to do with aesthetic use of bold and flow so maybe the original author would like the terms in bold left in.

Opinions welcome

--Sluffs (discuss • contribs) 23:31, 14 August 2015 (UTC)