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Old Jan 28th 2019, 06:54 AM   #1
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galaxy astrophysics

When we are in a data base like Galex find terms like (Declination) DEC>25deg, Size<10' (using antenna GBT , in L band. single pointing in L band) etc
Also in data bases like NED, GAlex, Simbad etc we find terms like coordinates of a Galaxy, RA, DEC, redshift, Active galaxy core (AGV
), spectrum , spectrum lines, wave length of observations.
Can anybody explain what the above terms mean and how astronomers find the values for those terms.
I know most of them are obvious but I don't want to make any mistakes and I have not much time.
Also a site where it describes the procedures to receive values for the above terms.
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Old Jan 30th 2019, 03:08 AM   #2
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When making any astronomical observations, many things are logged together with the images that describe the observations. This is referred to as metadata. Metadata differs depending on who/what is performing the observations, but generally all astronomers will write the following:

1. The position in the sky where the object is.
2. The conditions for the observation
3. The use of any special equipment (like filters)
4. Extra miscellaneous information on the target or observing situation

- The position of objects in the sky is expressed as the right ascension (RA) and declination (DEC). These are a bit like cooordinates which help to determine where to look in the sky to find an object. The RA is given as an angle to rotate clockwise (i.e. to the right) relative to a very precise direction at a standard date and position. DEC is similar, but for the vertical angle (along a meridian).

- The conditions might be cloudy, foggy, clear, stormy, humid, etc. Any weather conditions are usually written down and any readings for temperature, humidity or other sensors are written down also. All of these conditions give an idea of the "seeing", which is the word used to describe whether the conditions are adversely affecting the observations. A poor seeing might yield distorted or grainy images.

- Observations are often conducted with special equipment, such as filters and spectrometers, in addition to the actual telescope being used. So the telescope model name, mirror/lens information, spectrometer settings, filters, adaptive optics or any other equipment that can affect the images is specified.

- Sometimes particular information on the target is written down. For galaxies, it might contain the target name, the type of galaxy or redshift.
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Old Jan 30th 2019, 04:38 AM   #3
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I have never accessed any of the data-bases mentioned,
however I would have hoped that each data base would be accompanied by a "user guide" of some kind
which would describe, in detail, the precise interpretation of each of the search terms.

The terms mentioned are all standard astronomy terms, so one might expect that they have the same interpretation in all the data-bases.

However, be careful of that assumption!
There may be subtleties of definition which could upset cross data-base comparisons, if not recognised and adjusted for.

There is an old English saying "More Haste Less Speed"
Which basically means that if you try to rush (and particularly if you try to take short-cuts)
you will make mistakes or encounter obstacles, such that it will end up
taking longer than if you just worked through the problem at a careful methodical pace.
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Last edited by Woody; Jan 30th 2019 at 04:56 AM.
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