The astronomer

Gerard van der Puyl’s portrait of Nevil Maskelyne—just gorgeous. What a painter.

Nevil Maskelyne was the fifth Astronomer Royal at Greenwich Observatory. He proposed using the positions of the stars, planets and their moons as a method of calculating your position on Earth, just as Galileo had proposed using the moons of Jupiter as a universal clock. Maskelyne was a hard worker and determined to win that Longitude Prize. He believed that with accurate charts of stars’ positions, you could find longitude anywhere on Earth. At the Observatory, Maskelyne and a team of astronomers ‘worked feverishly through the year 1766, preparing tables for the new Nautical Almanac and Astronomical Ephemeris. Published first with data for the year 1767, it included daily tables of the positions of the Sun, Moon, and planets and other astronomical data, as well as tables of lunar distances giving the distance of the Moon from the Sun and nine stars suitable for lunar observations.’

Here’s Maskelyne in a nutshell:

Oops! Okay here’s Maskelyne in brief:

Sorry! Sorry! Here it is: Maskelyne’s idea was that you have a point zero of longitude—the Prime Meridian—as a reference point for time. Longitude is time measured in degrees. Each hour is 15° of longitude. When you’re at sea you take 2 measurements: the Sun’s position and the moon’s position. The Sun’s position tells you what your local time is; you find the moon’s position (the distance from the moon to one of the 9 suitable stars) in your almanac to tell what time it is at the Prime Meridian. The difference between your time and Prime Meridian time can be converted into degrees, which gives you your longitude.

You’re probably thinking: ‘Okay, Manders, how exactly do you measure the Sun and the moon? Usually when the moon’s out it’s nighttime.’ That’s an excellent point! You measure the Sun during the day and adjust the ship’s clock to the local time, maybe?

Back to the beginning of The Western Civ User’s Guide to Time & Space

3 responses to “The astronomer

  1. Pingback: Lunar distancing | John Manders' Blog

  2. Pingback: So long, and thanks for all the longitude | John Manders' Blog

  3. Pingback: Man-made moons | John Manders' Blog

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