Astronomical Data Used for Litigation
Astronomical Applications Dept. Astronomical Applications Dept.
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The U.S. Naval Observatory (USNO) does not furnish data specifically tailored for litigation. The data describing astronomical phenomena, provided by the USNO, are intended for public information and general use. The data are computed and are not reports of observed or recorded events. The computations assume certain conditions and the data might therefore not be relevant to the facts at issue in a specific case. The data are provided without seal or certification regarding authority, custody, or authenticity, and acceptance by a court is not guaranteed.

Astronomical data are sometimes needed for civil or criminal court proceedings, especially where there is an issue of the amount of natural illumination available during the incident in question. Both astronomical and meteorological information may be needed in such cases.

The USNO does not collect or maintain records or systems of records of astronomical phenomena—for example, observed times of sunrise, sunset, twilight, or Moon phases— that might be useful for litigation. Such observations are not regularly made by any agency of the U.S. Government, since the relevant data can be computed for past or future dates to sufficient accuracy for all practical purposes. In this sense, astronomical data are different from weather data, which must be observed and recorded.

The Astronomical Applications Department of the USNO provides Web pages where these computations can be made online. For example, the Web page titled Sun and Moon Data for One Day provides sunrise/sunset, moonrise/moonset, and twilight times along with Moon phase for any specific date and place. Other astronomical information can be found in the department's Data Services pages. There is no charge for these data services. These kinds of astronomical computations can also usually be performed by any observatory, planetarium, university astronomy department, or other competent authority.

In addition, the USNO can provide, by mail, tables of sunrise/sunset, civil twilight, or moonrise/moonset times for a specific location for an entire year. Each table produced for mailing costs $15.00, which must be prepaid by check or money order. Download the order form, fill it out, and return it to the Naval Observatory (ATTN: N3AA, 3450 Massachusetts Ave. NW, Washington, DC 20392) along with payment. The tables are provided without seal or certification regarding authority, custody, or authenticity.

If a litigant desires a signed letter or some other type of "certified" document containing the calculated data, there are several private-sector sources that can be used. Resources that can assist you in finding information and expert testimony are listed below under Forensic Services.

For further information on this subject see:

In particular, attorneys should review the last reference prior to making any requests for information or testimony. The instruction includes this statement: "DoN [(Department of Navy)] personnel... shall not provide, with or without compensation, opinion or expert testimony concerning official DoD [(Department of Defense)] information, subjects, personnel, or activities, except on behalf of the United States or a party represented by the Department of Justice, or with the written special authorization required by this instruction."

Weather information is not available from the USNO. Official weather records (cloud cover, precipitation, etc.) compiled throughout the United States are available from:

NOAA National Climatic Data Center
Federal Building
151 Patton Avenue
Asheville, NC  28801-5001
Phone: (828) 271-4800

Civil time (zone time, daylight time) legally in effect at locations within the United States is determined by the Secretary of Transportation. Information may be obtained from:

Office of the General Counsel
Department of Transportation
Room 10424
400 - 7th Street SW
Washington, D.C.  20590
Phone: (202) 366-4723


The following are sources of information that can assist in locating expert support for forensic inquiry, interpretation of data, and litigation. This list is not exhaustive and is not to be construed as an endorsement by the U.S. Government of any services, or of companies or individuals recommended by the services.

The Technical Advisory Service for Attorneys refers experts for a range of forensic and consulting services. Presently offers 22,000 experts in 5500 categories. Telephone consultation advised.

Technical Advisory Service for Attorneys
1166 Dekalb Pike
Blue Bell, PA  19422-1853
Phone: (610) 275-8272 or (800) 523-2319

The American Weather and Climate Industry Association has a list of U.S. commercial weather companies and services.

American Weather And Climate Industry Association (AWCIA)
1015 Waterwood Parkway, Suite J
Edmond, OK 73034

The National Association of Professional Accident Reconstruction Specialists can provide information on forensic issues arising out of various types of accidents.

P.O. Box 65
Brandywine, MD  20613-0065
Phone: (301) 843-1371

The Directory of Certified Consulting Meteorologists is a listing of weather experts by specialty and by state/country. Includes forensic - 44, expert testimony - 73. Published by the AMS.

American Meteorological Society
45 Beacon Street
Boston, MA  02108-3693
Phone: (617) 227-2425 to obtain directory

Astronomical information can often be obtained locally from astronomers or celestial navigation instructors at public and private schools, colleges, observatories, planetariums and maritime academies.