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A young lawyer from Illinois was faced with a dilemma. A witness claimed to have seen his client at the scene of a murder by the light of the full moon. In that humble county courthouse, Abraham Lincoln used an early volume of The American Ephemeris and Nautical Almanac to prove there was no moon visible at the time of the crime, discrediting the witness. This example is the first well-known use of astronomical data in support of the legal profession. Legal librarians and paralegal staff are often asked to locate certified statements of the sunrise or sunset for use in litigation. Establishing the time an incident occurred is often critical to the outcome of a case. Knowing the height and direction of the sun at a specific time can strengthen or discredit a witness who claims to have clearly observed an incident. Astronomical data can establish an objective foundation for arguing certain issues. Most people use their perception of time to express when something happened: “just before nightfall,” “right after sundown,” “before dusk,” and “it was still light out” are common examples. Supplying the time of sunset on the date in question can change ambiguous and subjective observations into definitive statements. “Just after sunset” translates to “about 6:07 p.m.” “Just before dark” becomes “approximately 6:35 p.m.” Some states use terms like dusk and onset of darkness in their laws and regulations, and the words dusk, twilight, and nightfall are often heard in the courtroom. But how precise are these concepts? Dusk, by definition, is the period “tending toward darkness.” Nightfall has a similar ambiguity. The term twilight, on the other hand, has a specific scientific definition, which, when properly explained to a jury, transforms a vague statement that is open to individual interpretation into definitive terms with an objective foundation. SUNRISE, SUNSET The time of day an event occurred could even determine the type of offense charged, in a criminal case. For example, New York’s law on burglary differentiates between day and night. Unlawful entering during daylight is a misdemeanor; at night, it is a felony offense. Lawmakers defined the generic phrase hours of darkness as starting 30 minutes after sunset and continuing until 30 minutes before sunrise. Once the precise time of sunset or sunrise is established for the place and the day in question, law enforcement officials can properly charge and prosecute criminals under this statute. Using data for a location some distance from the scene of the crime can result in improper charges being filed. Because the sun’s shadow travels about 16.25 miles every minute, the time of sunrise or sunset published in newspapers and periodicals for that day is generally not accepted in most jurisdictions since these are not authoritative sources. The U.S. Naval Observatory is the authority, by act of Congress, for all astronomical data in the United States. However, a federal regulation prohibits the USNO from providing expert witnesses for use in litigation, unless the federal government is a party to the action. The Navy judge advocate general has determined that performing the calculations and providing a “certified” statement is a form of acting in the capacity of an expert witness. Astronomical data, as used in litigation, is based on the motions of the earth and moon around the sun. Astronomers extensively studied the motions of these bodies for a number of centuries and devised a series of formulas still used today. Because astronomical events occur simultaneously over a large portion of the earth, astronomers created a system to calculate the time of an event in question for any location worldwide. This astronomical data was intended for use by marine navigators and was based on the time a particular phenomenon would be observed at the Greenwich Meridian. The American Ephemeris and Nautical Almanac, published by the USNO, in cooperation with Her Majesty’s Nautical Almanac Office, are recognized worldwide as a standard reference source for astronomy and navigation data. Information for any location on earth, for any date (past or future) can be determined with sufficient accuracy for civil matters, through a series of standard calculations. TWILIGHT ZONE A simple examination of the issues involved in the case will determine what data will be required to support or refute a point of contention. Many people mistakenly ask for the time of sunset, hoping to establish how dark it was at a particular time, but the more appropriate time to determine is twilight — the period before sunrise and after sunset. Twilight is the period where light is refracted through the atmosphere to the earth’s surface. The light level during the various periods of twilight ranges from light that’s undetectable by the human eye to where the natural light is sufficient to conduct normal outdoor activities without additional (artificial) lighting. The later period, known as “civil twilight,” is when the sun is less than six degrees below the horizon. A rule of thumb definition is: the period when a person can read a newspaper outside, without lights, while the sun is below the horizon. There are also periods called “nautical twilight” and “astronomical twilight” that are of little importance outside of a few specialized professions. In certain matters, lighting conditions can be an issue. Was there sufficient light to see an incident clearly and identify the individuals involved? Was there enough light to see colors clearly? Was there too much light? When the sun is low on the horizon, it can blind a witness or a driver. And the amount of moonlight on a particular night can be an important fact in some suburbs and most rural areas. FINDING AN EXPERT Astronomers are a primary source of people who could be used as expert witnesses, but their explanations may be too technical to be understood by the general public. Their work generally involves matters far beyond the scope of the earth, sun, and moon, such as the search for extra solar planets or the search for proof of the theory involving dark matter in the universe. Few astronomers want to deal with anything as simple as calculating the time of sunset, let alone take time to appear in court and explain their data in simple terms. The second profession that uses raw astronomical data regularly is the professional marine or aviation navigator. Navigators who use celestial navigation regularly calculate the rising, setting, and positions of the sun and moon to verify the position of a ship or aircraft, and to confirm the accuracy of electronic navigation equipment. Marine navigators are also responsible for weather and oceanographic observations, which gives them a strong background to discuss the effects of weather on lighting conditions. But, by the nature of their work, navigators are often traveling and can seldom commit to be available for testimony in a deposition or trial. Professional land surveyors are a third option. Land surveyors traditionally used the sun’s position to calculate a location’s latitude and longitude and were familiar with methods of calculating astronomical data. This field is undergoing great changes with the use of the Geographic Information Systems, the foundation of the State Plane Coordinate system, and the Global Positioning System. Some surveyors, however, still use astronomical data to verify old land titles. A surveyor with long experience in the field is more likely to be able to perform the calculations to support a legal action. Patrick McCarthy spent over 20 years in the U.S. Navy as a quartermaster and in the Nautical Almanac Office of the U.S. Naval Observatory responding to requests for astronomical data from military organizations, governmental agencies, and the public. He is the founder of Astronomical Facts, a service company that can provide certified astronomical data support in many fields, including criminal and civil trials and investigations. He can be reached at [email protected].

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