This article is authored by a Forensic Astronomer and is offered for research and public education, with proper citation.
A Forensic Astronomer provides specific details concerning the natural lighting conditions, any date and location, supporting criminal investigations, accident reconstruction, and legal proceedings.

Published in the "National Paralegal Reporter" August/September 2003 - Volume 28, Number 1 In Search of a Sunset? By Patrick McCarthy Many legal professionals have spent numerous, frustrating hours searching for some source of certified data concerning the Sun or Moon for use in litigation. While stationed at the U.S. Naval Observatory (USNO) I may have spoken with a number of you that were seeking data about the time of sunset for use in a trial. Understanding your frustration, this article will attempt to explain why there is such a problem obtaining data, why the USNO cannot provide certified data, and where you might find an expert who can provide the information you require. Why is Astronomical Data so hard to obtain? Astronomical data, as used in litigation, is based upon the motions of Earth and Moon around the Sun. The astronomers have extensively studied the motions of these bodies for a number of centuries. Astronomy's greatest minds have expressed the results of these studies as a series of formulas. Rather than creating a system of observation records for each location, they created a system to calculate the event in question for any location worldwide. Astronomical data was initially published as a reference for navigation at sea. The raw data for each year is published in standard reference publications such as the Astronomical Almanac produced by the USNO. Since the first American Ephemeris and Nautical Almanac was published in 1855 the Nautical Almanac Office of the USNO has been recognized worldwide as an authority in astronomical data. The data is presented in standard publications as the time of occurrence of particular phenomena (i.e. sunrise) as observed on the Greenwich Meridian. Through a series of standard calculations the time that the phenomena in question happened at a particular location can be expressed with a high confidence in the results. Because the motions of the bodies involved are so well understood there is no longer any requirement to regularly conduct or record observations. Attempts to subpoena "records" or submit Freedom of Information Act Requests to the USNO are futile. There simply are no "records" for the specific location listed in your request. There is no system of observing or recording observations in place like the U.S. Weather Service because the data is sufficiently accurate for normal civil use. Why the U.S. Naval Observatory can not provide certified statements. The USNO staff does not provide certified statements of astronomical data for use in litigation as a result of provision of Title 5 Code of Federal Regulations (5 CFR 2635.805a). This section specifically prohibits employees of the Executive Branch of the government from acting in the capacity of expert witness in any matter where the government is not party to the action. The USNO has determined that performing the calculations and providing a "certified" statement is a form of acting in the capacity of an expert witness specifically proscribed by the CFR provisions. What do you need? An understanding of what data you require is just as important as finding someone who can supply the data. A brief analysis of the issue in question will determine what information is needed. If the issue is one of whether it was dark or not, the time of Civil Twilight is much more appropriate than the time of sunrise or sunset. There is a period before sunrise and after sunset, known as twilight, where the available natural light is sufficient to conduct normal outdoor activities without additional (artificial) lighting. This period is known as Civil Twilight and by strict definition it is the period when the Sun is less than six degrees below the horizon until the Sun breaks (rising) or vanishes (sets) from the horizon. There are also periods of Nautical and Astronomical Twilight that are of little importance outside of a few specialized professions. When the local laws specify requirement that is directly referenced to the time of sunrise or sunset, such as when automobile headlights must be illuminated, there is a clear need for the local time of sunrise or sunset data. Some local laws use generic or ambiguous terms like dusk or nightfall. These terms have no clear scientific definitions and create a confused situation because the terms call for subjective rather than objective treatment by the parties involved. Witnesses may use terms like "just before dark," "right after sunset," "it was still light out." These statements are open to interpretation by the listener as to when an event happened. I recently provided Sunset and Civil Twilight data in a medical malpractice suit to establish the time of an injury based upon witness statements similar to those listed above. By establishing a 30-minute time frame during which the injury happened the plaintiff was able to establish that a significant period lapsed between the time of the injury and when treatment was obtained. An expert in astronomical phenomena can examine the celestial situation around the time of an incident and provide the appropriate data or provide a clear explanation of the situation. With this scientifically based explanation of the natural lighting situation at the time of an incident all parties (and jurors) are forced to use the objective data rather than their own interpretation of what the lighting conditions were. So where are the experts? Few professions have ever used the astronomical data such as that published by the USNO. The astronomers are a primary source of people who could be used as experts but their explanations may be too technical for understanding by the general public. Their work generally involves matters far beyond the scope of the Earth, Sun and Moon, often involving the search for extra solar planets or seeking the proof for the theory involving dark matter in the universe. Few astronomers want to deal with anything so simple as calculating the time of sunset let alone take time to appear in court and explaining their data in simple terms. The second profession that uses the raw astronomical data regularly is the professional marine or aviation navigator. The navigators that use celestial navigation regularly calculate the rising, setting and positions of the Sun and Moon to verify the ship or aircraft position and validate the position determined via electronic means. Marine navigators are also responsible for weather and oceanographic observations, which gives them a strong position to discuss the effects of weather on lighting conditions. By the nature of their work, navigators are often traveling and can seldom commit to be available for testimony in depositions or trial. A third profession that has used the astronomic data in their field of work is professional land surveyor. Land surveyors have traditionally used the sun's position to calculate a location's latitude and longitude and are familiar with methods of calculating astronomical data. This field is undergoing great changes with the availability of electronic position instruments and I am not familiar with that profession's current use of astronomical data. Perhaps people with long experience in the field can perform the calculations to support a legal action. A final note. Astronomical data can be calculated for a specific location, such as a street address, not just some city or town center that may be miles away from the location of interest. Pick an expert that can discuss the data in technical terms but who can also present the data in terms average people can understand. Finally, make sure they can commit the time necessary to support the entire legal process. About the author Patrick McCarthy spent over 20 years in the U.S. Navy as a Quartermaster, responsible for ship's navigation. His final duty assignment in the Navy was in the Nautical Almanac Office of the U.S. Naval Observatory where he was the point of contact for all requests concerning astronomical data from military organizations, governmental agencies and the public between 1995 and 2001. Upon retirement in 2001 he founded Astronomical Facts, a service company, in response to the lack of any source of certified astronomical data. Astronomical Facts can provide certified astronomical data support in many fields including criminal and civil trials and investigations, insurance claim examinations, special event planning, professional photography and film production. Contact Information