Observing nights and timestamps (valid ranges) are important concepts in AWE. These concepts are inherently confusing and some understanding of our conventions is necessary. This HOW-TO describes how to work with dates and times.
When an astronomer does observations with a telescope this happens during the night at that telescope. We define a night for a particular telescope as the period between noon and noon the next day at that telescope. This concept is only valid in terms of local time. Since all relevant times that are stored in the database are stored in UTC, depending on the telescope, a conversion from local time to UTC and vice versa is necessary.
The following raw science images observed by WFC@INT are observed in the same night. This is the night of 30 March 2005 in our terminology.
WFC.2005-03-30T19:18:55.8.fits WFC.2005-03-30T20:00:29.6.fits WFC.2005-03-30T21:11:19.7.fits WFC.2005-03-30T22:32:10.8.fits WFC.2005-03-30T23:12:01.1.fits WFC.2005-03-31T00:00:41.9.fits WFC.2005-03-31T01:06:57.2.fits
Based on input from the user, namely the night for which to process data, both science images and calibration images are selected in the database and used/created. This input is always called "date" and is an argument for command line driven interfaces as well as the web services.
awe> task = ReadNoiseTask(date='2000-04-28', instrument='WFI', chip='ccd50') awe> dpu.run('ReadNoise', d='2000-04-28, i='WFI') awe> query = RawScienceFrame.select(date='2000-04-28', instrument='WFI', ... object='CDF4_B_1') awe> for f in query: print f.DATE_OBS ... 2000-04-29 00:04:29.00 2000-04-29 00:04:29.00 2000-04-29 01:05:58.00 2000-04-29 00:04:29.00 2000-04-29 00:04:29.00 2000-04-29 00:04:29.00 2000-04-29 01:05:58.00 2000-04-29 01:05:58.00 2000-04-29 01:05:58.00 2000-04-29 01:05:58.00 2000-04-29 00:04:29.00 2000-04-29 01:05:58.00 2000-04-29 00:04:29.00 2000-04-29 00:04:29.00 2000-04-29 01:05:58.00 2000-04-29 01:05:58.00
To be able to automatically select appropriate calibration files (bias, flat etc.) from the database for a given science image or as a result of the "date" input by the user, timestamps are assigned to each calibration file that define a period for which this calibration file is valid. All dates that are stored in the database and used for this purpose are in UTC. See also table . Calibration files are valid for a certain multiple of observing nights, depending on the type of file.
A night in terms of UTC is determined by converting "noon" to UTC. No correction is made for any daylight saving time. The shift in the timestamps is exactly equal to the timezone of the instrument.