This section will given some pointers to resources for obtaining data related to astrometry. Links to some documents that describe concepts used in astrometry calculations are also present.
While working with data from the sources mentioned below, it is helpful, even critical, to subscribe to mailing lists and newsletters, that announce important updates. This applies to code libraries as well as data sources.
The Astronomical Almanac is a collection of information on most of the topics listed below. USNO Astronomical Applications division maintains a large repository of information on astronomical phenomena and astrometric data.
Information on delta_AT = TAI - UTC, leap seconds in UTC and other similar information are available from the International Earth Rotation and Reference Systems Service (IERS). See the section on International Earth Rotation and Reference Systems Service below.
Information on delta_AT also maintained in the file ftp://maia.usno.navy.mil/ser7/tai-utc.dat, which lists delta_AT values beginning from 1961 Jan. 1.
See files in the directory ftp://hpiers.obspm.fr/eop-pc/eop/eopc04_05 for listings that give delta_UT = UT1 - UTC values.
The last two resource are the easiest way for obtaining delta_AT and delta_UT, respectively.
PyTPM has a function pytpm.tpm.delta_AT() that gives the value for delta_AT for the given UTC. But this file has to be updated, using values in the tai-utc.dat file mentioned above. Notification of changes are notified through the IERS mailing lists. See International Earth Rotation and Reference Systems Service below.
Use the geo names search facility provided by the National Geospatial-Intelligence Survey for finding longitude and latitudes of places, using place and country names. Google Maps and Google Earth also give longitude, latitude and altitude information.
Websites of individual observatories may have information on their geodetic and geocentric positions.
Use the information in section on International Earth Rotation and Reference Systems Service for data on polar motion and other Earth orientation parameters.
Positions and orbital elements of astronomical objects and Earth satellites, including Earth-Sun ephemerides.
Definitive collection of information on minor planets, including orbital elements.
The Asteroid Orbital Elements Database
By Edward Bowell, based on astrometric observations downloaded from the Minor Planet Center and “updated daily”.
JPL ephemerides and HORIZONS online ephemerides generator
JPL planetary ephemerides can be downloaded from the JPL ephemerides site.
HORIZONS is an online system for generating custom ephemerides. Output can be generated in the form of osculating elements as well as in the form of Cartesian vectors (position, velocity and acceleration). Ephemerides for more than 60 satellites are also available.
Data on solar system objects observed with the Flagstaff Astrometric Scanning Transit Telescope is available at http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/solsys.
Earth satellites
NORAD elements can be obtained from CelesTrak.
NASA space flight center has orbital elements for ISS.
Fundamental physical data, constants and physical properties of astronomical objects.
Physical data and fundamental constants.
CODATA at National Institute of Standards and Technology (NIST).
Internationally recommended values of the fundamental physical data.
Physical Measurements Laboratory at NIST, especially the Physical Reference Data section.
Data for solar system objects
IAU Working Group on Numerical Standards for Fundamental Astronomy
IAU/IERS approved physical and astronomical constants.
NSFA website: http://maia.usno.navy.mil/NSFA.html.
Examples of software similar to TPM and PyTPM. Some of these can be used to calculate quantities such as rising and setting time for Sun and Moon, phases of Moon and others.
Astrometry catalogs i.e., catalogs of accurate positions and proper motion ; data can be accessed using the ViZier service.
USNO-B1.0 is the latest catalog from the USNO Precision Measuring Machine project. It contains over 1,000,000,000 entries and provides positions, magnitudes, and proper motions for each object.
A new determination of mean positions and proper motions on the ICRS system by combining USNO-B1.0 and 2MASS astrometry.
NOMAD (Naval Observatory Merged Astrometric Dataset)
NOMAD is a simple merge of data from the Hipparcos, Tycho-2, UCAC-2 and USNO-B1 catalogs, supplemented by photometric information from the 2MASS final release point source catalog. The primary aim of NOMAD is to help users retrieve the best currently available astrometric data for any star in the sky by providing these data in one place.
These documents explain concepts such as precession, nutation, time scales and others related to astrometry. The various papers mentioned in these documents are also important sources of information on astrometry related concepts.
NOVAS Manual
SLALIB Manual
Astronomy on the Personal Computer
This books is essentially a reference manual for the C++ software that is distributed with it. It has good explanations of concepts such as orbital elements, precession angles and others.
Step-by-step instructions on performing astrometry calculations using a calculator. Great book for understanding basic ideas in astrometry.
The SOFA cookbooks, Tools for Earth Attitude and Time Scales and Calendar Tools, are perhaps the best documents to start with. Spherical Astronomy by Robin M. Green and Fundamentals of Astrometry by Jean Kovalevsky and P. Kenneth Seidelmann, are two relevant textbooks.
USNO Astronomical Applications
Services such as date calculations, setting and rising time and others. Information on astronomical concepts behind the above calculations are also provided.
Links to astrometric catalogs such as NOMAD, UCAC, USNO-B1.0 etc., . Observations of planetary satellites and minor planets are also provided.
USNO is the International Earth Rotation and Reference Systems Service (IERS) Rapid Service/Prediction Center (RS/PC) for Earth Orientation. Most of the information in IERS bulletins are issued from USNO.
Information on obtaining precise time (UTC).
JPL SSD collects information on orbits, ephemerides and physical characteristics of solar system objects.
SOFA, or the SOFA Board, is responsible for implementing the definitive algorithms for standard models used in Astronomy. This organization works under IAU Division 1.
Implementations of the algorithms in Fortran 77 and ANSI C are made available by SOFA.
SOFA has an email service that sends notifications of software releases and other information.
IERS is responsible for defining and determining Earth orientation, International Terrestrial Reference System/Frame, International Celestial Reference System/Frame and geophysical fluids data.
IERS also provides information on leap seconds and DUT1, which are related to Earth orientation. It was established by the IAU and the International Union of Geodesy and Geophysics.
IERS has an email notification service that delivers all their data bulletins and messages:
Bulletin A (weekly)
IERS Bulletin A contains Earth orientation parameters x/y pole, UT1 - UTC and their errors at daily intervals and predictions for 1 year into the future.
But also see files in the directory ftp://hpiers.obspm.fr/eop-pc/eop/eopc04_05 for listings that give UT1 - UTC values. These are probably easier to use. For example the file eopc04_IAU2000.62-now in the above directory gives UT1 - UTC values, in addition to many others, for the appropriate period.
Bulletin B (monthly)
IERS Bulletin B provides current information on the Earth’s orientation in the IERS Reference System. This includes Universal Time, coordinates of the terrestrial pole, and celestial pole offsets.
Bulletin C (bi-annual)
Announcement of leap seconds in UTC and information on UTC-TAI.
Bulletin D (irregular)
Announcements of the value of DUT1 = UT1 - UTC to be transmitted with time signals with a precision of ±0.1s.
Messages (irregular)
The IERS Messages contain short and rapid information about the IERS and its products for contributors and users.
See IERS data products page page for all data provided by IERS. The “directory” http://maia.usno.navy.mil/ser7/ contains collection of files that has data from all published bulletins, for example bulletin B. For information of the contents of various bulletins see appropriate files in ftp://hpiers.obspm.fr/iers/bul.
See files in the directory ftp://hpiers.obspm.fr/eop-pc/eop/eopc04_05 for listings that give UT1 - UTC and other Earth orientation parameters.