Online Catalogs and Archives
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In recent years there has been a fundamental shift in the way we can conduct astrophysical research. This has been due to the advent of:
- Astronomical photography
- Scanner technology
- CCD technology
- Cheap (and therefore vast) hard-space
- The Internet
- Fast data transfer rates
In combination, these technologies have allowed the digital storage of vast quantities of astronomical data. For example, the Multi-mission Archive at STScI
contains around 17Tbs of data, of which it distributes around 2.5Tbs per year. All observatories now have, or are constructing, online data archives, and with
the development of grid computing and large format panoramic cameras, the amount of archived data is set to increase dramatically over the next few years.
It is now possible to conduct original astronomical research without the need to collect new data. In fact, several agencies, including STScI and NSF, will
now fund purely archival research.
Catalogs
Contain specific data taken from archives, surveys and/or published papers.
For example:
- Hyperleda. The physics and evolution of galaxies.
- SIMBAD. Basic data, cross-identifications, bibliography and measurements for astronomical objects outside
the solar system.
- NED. Nasa/IPAC Extra-galactic Database.
In most cases, it is likely that you will need to query more than one of these catalogs in order to retrieve all the information about your object of interest.
Archives
These contain the actual raw and reduced data. If you need to work directly
with archived data, e.g., extract a spectrum, perform specific aperture
photometry, or fit a surface brightness profile, then you will need to retrieve
the data in some of these archives. Usually, data can be retrieve via anonymous
FTP and/or by setting up a user account. Generally, data that has been in the
archive for more than 12 months is publicly available; it's proprietary period
(designed so that the original PI has time to analyze the data first) will be
over.
There are archives for data from all wavelengths, most of them, e.g., VLA, DSS, HST, GALEX, FUSE, XMM, are available from MAST.
However, a few extra useful ones may be:
Batch Jobs
In some cases, you may need to submit a large number of queries to the data catalogs and archives. In these cases, many databases allow you to submit a batch job
(basically a set of search criteria) that will query the whole database and return a formatted list of all targets matching your search criteria.
For example, in the 2MASS Extended Source catalog, you can upload a table of sources with which to query the whole catalog:
\EQUINOX = 'J2000.0'
| name | ra | dec | radius |
| char | double | double | double |
M31 10.684710 41.268749 10
2MASXJ06111689-6609210 92.820389 -66.155838 50
Making finding charts
One of the most useful tools, in my opinion,
is just a part of the
SIMBAD offerings:
the Aladin
application is designed to display (small) regions of the sky
and produce overlays from various catalogs.
I use it almost every week to make finding charts
and look up quick properties for objects I am following.
Some time ago, I wrote a detailed, step-by-step guide
to show one way to use Aladin.
Ephemerides
Every now and then, you may need to find some information
about a body within our own solar system.
For example, friends may ask you,
"What's all this about Mars becoming as large
as the Moon on August 27, 2008?"
If you are interested in objects within the solar system,
you need a tool which can account for orbital motions.
There are several choices:
- You can sometimes use "planetarium" programs
which show the locations of objects in the sky
for any particular time and place.
I use the following two, because they are free and work well
for me:
- If you want to step off the Earth's surface and view
events from any place within -- or outside --
the Solar System, try
- If you don't care about the pretty pictures and just want
the numbers -- or if you need the VERY BEST positions --
then check out
Your assignment
You must answer the following questions in writing.
Add as much information as you can in each case.
In addition to the resources mentioned above, you
may find these programs very useful.
They are open-source programs which allow you to examine
FITS files of different types.
-
FV works well on FITS files which contain
tables
-
ds9 display FITS images nicely
The questions:
- There is a galaxy at RA = 13:00:52, Dec = +28.2158.
It is a member of the Coma Cluster of galaxies.
- what is its morphological type? spiral? elliptical?
- roughly how far away is it from the heart of the
Coma Cluster of galaxies? Provide your
answer in arcminutes or degrees.
- what is its magnitude in (any) optical passband?
- what is its magnitude in (any) infrared passband?
- is it a strong radio source?
- is it a strong X-ray source?
- what is the radial velocity if this galaxy?
Provide both the speed and direction (towards us
or away from us)
- a short distance away from this galaxy lies a foreground
star in our own Milky Way
- how far away is this foreground star?
Provide an answer in arcminutes.
- is this star
hotter than the typical stars in the galaxy,
cooler than the typical stars in the galaxy,
or about the same temperature
as typical stars in the galaxy?
Justify your answer.
- As mentioned above, there has been a repeated "rumor"
that on a certain date, Mars would appear in the sky to be
as large as the Earth's Moon.
One of the most recent dates mentioned was Aug 27, 2008.
- On that date, how far as Mars from the Earth?
- How large did Mars appear on that date?
Give its size relative to the Moon's apparent size --
was its angular diameter half the Moon's angular
diameter, or one-quarter, or one-tenth, or what?
You can look at
a comparison I made with Celestia
to see how silly this story is ...
- There is a "mystery object" of some type at RA = 228.48174 degrees,
Dec = -59.1358 degrees.
- What kind of object is it?
- In what regions of the electromagnetic spectrum
do we detect this object?
Answer "yes" or "no" for each of the following:
- radio
- near-IR
- visible
- X-ray
Bonus for additional regions of the spectrum,
if you can provide them.
- Is there any way to estimate the age of this
object? If so, provide a value for the age.
- Is there any way to estimate the distance of this
object? If so, provide a value for the distance.
This page maintained by Michael Richmond.
Last modified Sep 02, 2008.
Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.
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