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Our sky chart shows the waxing crescent moon and the blazing planet Jupiter as viewed from North America. However, no matter where you live, it should be a piece of cake to find Jupiter this evening. Look for the very brilliant star-like object near tonight’s moon, and that will be Jupiter.
For us in North America, the moon will shine at roughly the same distance from Jupiter tonight that it did yesterday. However, in the world’s eastern hemisphere – Europe, Africa, Asia, Indonesia, Australia and New Zealand – the moon will be appreciably closer to Jupiter this Monday evening. At a given hour for any date, the moon appears farther west relative to the background stars and planets in the eastern hemisphere than it does in the western hemisphere (the Americas).
In fact, a most brilliant celestial navigator named Nathaniel Bowditch (1773-1838) was able to reference the moon’s position relative to key stars and/or planets to determine longitude at sea – without a chronometer. How many people today could find longitude with a chronometer?
Galileo (1564-1642) proposed using the four major moons of Jupiter to figure longitude at sea. Although this method never proved viable in the rough and tumble seas, it worked like a charm on land.
As you watch the moon and Jupiter tonight, keep in mind that these two orbs once enabled navigators of old to determine longitude centuries before the advent of GPS (Global Positioning System) in 1973.
What is the bright object up before dawn in January?
Written by Bruce McClure
Astronomy Picture of the Day from NASA/JPL
U.S. Naval Observator Astronomical Information center
The York County Astronomical Society
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