Frequently Asked Questions
This is not intended to be a substitute for the actual documentation, which includes detailed information on photometry, astrometry, and object classification. Rather, this page has sample replies to often-heard comments about the on-line catalogs.
Questions we have answered on this page:
- How do I refer to MAPS data in my published research?
- How do I get the entry for one specific MAPS catalog object?
- I would like to just get the whole catalog to examine at my convenience. Is that possible?
- How can I find out which fields are available online?
- How many bytes will the output consume?
- Why is there a gap in the data I requested?
- Have any science papers been produced with the MAPS and MAPS data?
- How did you guys do this? What software did you use?
- What is the best time to access your site, in terms of WWW usage?
- Why are object queries in Galactic coordinate so much slower than in B1950 or J2000?
How do I refer to MAPS data in my published research? [back to top]
We have a policy for citations. Your acknowledgement is appreciated.
How do I get the entry for one specific MAPS catalog object? [back to top]
This can be accomplished through direct SQL query. Read the documentation for information.
I would like to just get the whole catalog to examine at my convenience. Is that possible? [back to top]
Lucky for you, it is! The instructions for this are on our HOWTO page, which is currently on hiatus. Check back.
How can I find out which fields are available online? [back to top]
The most general way to do this would be running the following SQL query:
SELECT ptable FROM plates WHERE true;If you are interested in certain coordinates, use our field finder.
How many bytes will the output consume? [back to top]
Each entry consists of about 300 bytes, so multiply that by the number of objects.
Why is there a gap in the data I requested? [back to top]
Stars brighter than about magnitude 6 and large regions of nebulosity have poor S/N characteristics and are not included in the databases. Examples include the overexposed area about Sirius, the bright nebulosity about the Pleiades, and the core of M31. There are more suitable sources of catalog information on these objects.
Image editing of plates will, therefore, lead to circular and/or rectangular areas devoid of objects. Please note that no real information is lost in this process. Also, even with this precaution the diffraction halos around remaining brighter objects produce many false O-to-E matches, most of which become classified as galaxies.
To find out which areas of a plate have been edited, view the field info for that POSS 1 field.
Have any science papers been produced with the MAPS and MAPS data? [back to top]
A list of papers published using APS data is available.
How did you guys do this? What software did you use? [back to top]
The calibration process is described in detail in the main documentation.
What are the best times to access your site, in terms of WWW usage? [back to top]
With our new server, our capacity to serve queries quickly has increased greatly. Typically, the best time to run large queries is during the late evening (CST). It should be noted that cron jobs run from midnight until three in the morning, which can slow down the machine. If your query requires special consideration, please contact us.
Why are object queries in Galactic coordinate so much slower than in B1950 or J2000? [back to top]
In a nutshell, this is because the POSS I plates were shot with their boundaries roughly aligned to the celestial equator and not the the Galactic equator. Therefore the "limits" of POSS I fields in Galactic coordinates tend to be much broader. Therefore, when the software checks which POSS I fields have limits encompassing a given sky box, there will often be POSS I fields matched that do not actually overlap the given sky box even though the "limits" of that POSS I field in Galactic coordinates.
If the field is large enough (many degrees in width), queries in Galactic coordinates should not be much worse than those in B1950.0 or J2000.0.