STScI Logo

obs noao



observatory -- Examine and set observatory parameters


observatory command obsid [images]


command = "list" (set|list|images)
Command option which is one of "set", "list", or "images". The set command sets the default observatory task parameters for the specified observatory. The list command lists the observatory paramters for the specified observatory but does not modify the task parameters. The images command lists the observatory parameters for a list of images. The list and images commands examine and verify the observatory parameters applied by other tasks using the observatory database facility.
obsid = "?"
Observatory identification to be set, listed, or used as the default for images without the OBSERVAT keyword. The observatory ID is one of those in the database (case ignored), the special string "observatory" to default to the environment variable "observatory" or the observatory.observatory parameter, "obspars" to select the parameters in the observatory task, or "?" to list the observatories defined in the database.
List of images to be examined with the "images" command. The images are checked for the OBSERVAT keyword to determine the observatory parameters to be listed, otherwise the observatory given by obsid is used.
verbose = no
Verbose output? Because there are a number of different ways in which observatory information is determine this option prints detailed information on how the observatory database and parameters are ultimately selected.

The default observatory used by tasks which use the special observatory identification "observatory". The value is one of the observatory names in the observatory database (case ignored) or the special value "obspars" to select the parameters defined in this task. There is no default to force users to set it at least once.
Observatory name.
Observatory longitude given in degrees west.
Observatory latitude in degrees. Positive latitudes are north and negative latitudes are south.
Observatory altitude in meters above sea level.
Observatory time zone. The time zone is the number of hours west of Greenwich or the number of hours to be added to local time to obtain Greenwich time.


This variable selects the observatory database. If not defined it defaults to noao$lib/obsdb.dat.
This variable selects the observatory entry whenever a task uses the observatory name "observatory". If not defined the value of the task parameter observatory.observatory is used.


The observatory identification for images is first sought under the image header keyword OBSERVAT. This always takes precedence over any other means of defining the observatory.



Some astronomical data reduction and analysis tasks perform computations requiring information about where the data was observed. For example a number of noao tasks make corrections for the airmass. Generally they look for an airmass in the image header and if it is not present they attempt to compute it from other image header parameters. The information about time and telescope coordinates of the observation are often in the image header but the observatory latitude is not. The task must get this information somehow.

Prior to IRAF V2.10 tasks generally had explicit parameters, such as latitude, with default values pointing (using parameter redirection) to the parameter of the same name in the observatory task. The user was required to know the values of the observatory parameters and manually change them for data from different observatories. In V2.10 an observatory database has been implemented. Observatory parameters are stored in a simple text file and tasks obtain observatory related parameters by specifying an observatory identification.

In general the information about the observatory should be directly associated with the image data. Unless stated otherwise in the description of a task, tasks which require observatory information will first look for the image header keyword OBSERVAT. The value of this keyword is the observatory identification used to index the observatory database. The task will then look up any observatory parameters it needs in the observatory database. Data from observatories that support this keyword will, therefore, always use the correct observatory parameters without user intervention. All observatories which export FITS image data are urged to adopt the OBSERVAT keyword (a keyword recommended by the FITS standard).

For image data which do not identify the observatory in this way and in tasks which do not operate on images (such as astronomical calculator tools), the observatory must be specified by the user. Most tasks provide an "observatory" parameter which either directly selects the observatory or use special values for defining the observatory with an environment variable or the parameters from the observatory task.

An observatory is specified by the identification name used in the observatory database. The names in the database may be listed using the observatory task as described below. If the desired observatory is not in the database a user may copy/create their own database and select it with the environment variable "obsdb", modify the standard database if allowed (any changes to the distributed version should be forwarded to iraf$, or use the special observatory name "obspars". The last option directly uses the parameters in the observatory task which can be set to any values using the normal parameter editing mechanism.

The default value for the observatory parameter in a task is generally "observatory". This special name directs the task to look first for the environment variable of the same name and then at the observatory parameter of the observatory task. The environment variable allows users or sites to set the default observatory in their login files and site defaults. Also it is simple to change the default observatory either with a reset command or the observatory command.

The observatory database is selected by the environment variable "obsdb". The default when the variable is not defined is the noao package library database file "noao$lib/obsdb.dat". The use of an environment variable allows users to permanently change the default database in the OS environment (when IRAF has access to it such as in UNIX systems) or in the startup IRAF environment as set in the "" or "" files. One can, of course, change it during a session with the set or reset commands. For sites which want to customize the observatory mechanism the environment variables can also be set and changed in the files "hlib$zzsetenv.def", "noao$lib/zzsetenv.def", and the template login file "hlib$".

An observatory database file consist of a simple list of keyword=value pairs with arbitrary whitespace allowed. An observatory entry begins with the observatory keyword and extends to the next observatory keyword or the end of the file. The observatory identification should be the same as the string used in the OBSERVAT image header parameter for data from that observatory. The default file noao$lib/obsdb.dat begins as follows:

# Observatory Parameters.  Taken from the Almanac.
# Observatories wishing to be added or make changes in the default
# distributed database should send information to

observatory = "kpno"
	name = "Kitt Peak National Observatory"
	longitude = 111:36.0
	latitude = 31:58.8
	altitude = 2120.
	timezone = 7

observatory = "ctio"

In summary, access to observatory parameters is now done by referencing the image header keyword OBSERVAT and, if not defined, determine the observatory name from a task parameter. The environment variables "observatory" and "obsdb" can be set by the user to select alternate observatories and observatory database files. For data without an observatory entry the observatory can be set to "obspars" or the user may make their own observatory database.


The observatory task serves a number of functions. It may be used to examine the observatory database, verify the observatory parameters which will be used by other tasks, particularly those operating on images, set the default observatory if not defined by other means, set observatory parameters explicitly, especially when there is no observatory database entry, and as a parameter set for tasks which explicitly reference observatory parameters. The verbose parameter also provides a detailed check of the steps used to determine the observatory database, observatory identification, and observatory parameters.

The command parameter takes the values "set", "list", or "images". The obsid parameter supplies the observatory identification and the images parameter is used to specify a list of images for the "images" command. The parameters are query parameters and so may be either queried or simply typed on the command line.

The "set" command prints the observatory parameters for the specified observatory and sets many of these in the observatory task parameters. This command is used to set the default observatory parameters for tasks where images are not used, the images do not contain the observatory id, or direct references to specific parameters with parameter redirection (for example ")observatory.latitude") are used.

The "list" command is similar to the "set" command except the task parameters are not modified. It is used to list observatory parameters. It is also use with the special observatory identifications to list the entries in an observatory database and verify the observatory to be used by tasks which do not operate on images. The special value "?" lists the entries in the database. The special value "observatory" lists the observatory defined by the "observatory" environment variable or that given by the observatory.observatory parameter. The special value "obspars" simply lists the observatory task parameters.

The "images" command lists the observatory information applicable to one or more images. In particular, the observatory identification is first sought in OBSERVAT image header keyword and, if not found, the obsid parameter is used. Often the default observatory is "observatory" to follow the same search path used by other tasks.

The verbose parameter prints additional detailed information. It prints the database used and whether it is selected by default (noao$lib/obsdb.dat) or by the "obsdb" environment variable. When the observatory is defined as "observatory" it indicates whether the observatory is defined by the environment variable "observatory" or by the observatory task. When listing images it prints the OBSERVAT keyword or the default observatory assigned.

For observatories not in a database the name, latitude, longitude, altitude, and time zone parameters may be set using eparam . The observatory id must be set to "obspars" in this case. These parameters will then be referenced by other tasks in which the observatory is specified as "obspars". This allows arbitrary observatory parameters to be set without creating or modifying an observatory database. However, it is advisable to create a local database and also send the observatory information to the IRAF group at NOAO for inclusion in the default database.


1. List the observatory entries in the database:

	cl> observatory list ? v+
	Using default observatory database: noao$lib/obsdb.dat

	default: Kitt Peak National Observatory
	kpno: Kitt Peak National Observatory
	ctio: Cerro Tololo Interamerican Observatory
	eso: European Southern Observatory
	lick: Lick Observatory
	mmt: Whipple Observatory
	cfht: Canada-France-Hawaii Telescope
	lapalma: Roque de los Mucachos, La Palma

2. Set the observatory parameters for Cerro Tololo:

	cl> observatory set ctio
	Observatory parameters for Cerro Tololo...
		observatory = ctio
		timezone = 5
		altitude = 2215.
		latitude = -30:09.9
		longitude = 70:48.9
	         name = 'Cerro Tololo Interamerican Observatory'
	cl> lpar observatory
	      command = "set"		Command (set|list|images)
	     argument = ctio		Observatory or images
	 (observatory = "ctio")         Observatory identification
	        (name = "Cerro Tololo...") Observatory name
	   (longitude = 70.815)         Observatory longitude (degrees)
	    (latitude = -30.165)        Observatory latitude (degrees)
	    (altitude = 2215.)          Observatory altitude (meters)
	    (timezone = 4)              Observatory time zone
	     (verbose = no)             Verbose output?
	        (mode = "q")            

3. Set the observatory parameters to use the environment variable "observatory" and verify it.

	cl> set observatory=cfht
	cl> observatory list observatory
	Observatory parameters for Canada-France-Hawaii Telescope
		observatory = cfht
		timezone = 10
		altitude = 4215
		latitude = 19:49.6
		longitude = 155:28.3
		name = 'Canada-France-Hawaii Telescope'

4. Change the default observatory database and verify verbosely:

	cl> set observatory="sco"
	cl> set obsdb="/local/iraf/obsdb.dat"
	cl> type obsdb$
	# Local Observatory Parameters.

	observatory = "sco"
		name = "Small College Observatory"
		longitude = 100:20.0
		latitude = 35:58.8
		altitude = 212.
		timezone = 6
	cl> observ set observatory v+
	Using database defined by 'obsdb' environment variable:
	Using obs... defined by 'obs...' environment variable: sco
	Using observatory parameters for database entry: sco
	Observatory parameters for Small College Observatory
		observatory = sco
		timezone = 6
		altitude = 212.
		latitude = 35:58.8
		longitude = 100:20.0
		name = 'Small College Observatory'

5. List the observatory assigned to some images with a default observatory determined either by the "observatory" environment variable or that set in the observatory task.

	cl> observ images observatory dev$pix,demoobj1
	Observatory parameters for Small College Observatory
		observatory = sco
		timezone = 6
		altitude = 212.
		latitude = 35:58.8
		longitude = 100:20.0
		name = 'Small College Observatory'
		Images: dev$pix (default observatory)
	Observatory parameters for Kitt Peak National Observatory
		observatory = kpno
		timezone = 7
		altitude = 2120.
		latitude = 31:58.8
		longitude = 111:36.0
		name = 'Kitt Peak National Observatory'
		Images: demoobj1 (OBSERVAT keyword)

6. Set explicit observatory parameters:

	cl> epar observatory
	<set observatory parameters>
	cl> observ list obspars
	Observatory parameters for North Pole
		observatory = obspars
		timezone = 0
		altitude = 0.
		latitude = 90.
		longitude = 0.
		name = 'North Pole'

7. Use observatory parameters in expressions:

	cl> observ set kpno
	Observatory parameters for Kitt Peak National Observatory
		observatory = kpno
		timezone = 7
		altitude = 2120.
		latitude = 31:58.8
		longitude = 111:36.0
		name = 'Kitt Peak National Observatory'
	cl> =
	cl> = sin (3.14159/180 *


Tasks in astutil, imred, onedspec, and twodspec.

Source Code · Search Form · STSDAS