Moon and Planets

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Moon and Planets

There’s a traffic jam in the early morning twilight tomorrow. Three planets will congregate near the Moon. There’s not much time to look at them, though. And you need a clear horizon — any buildings or trees will block the view.

The brightest of the planets is Jupiter, the giant of the solar system. It’s to the upper left of the Moon. Next-brightest is Mercury, the Sun’s tiniest major planet. It’s to the left of the Moon. And the faintest planet is Saturn, to the upper right of the Moon.

For the moment, Mercury shines at magnitude zero — the starting point for the brightness scale astronomers have used for millennia. In this system, the lower the number, the brighter the object. So magnitude zero is quite bright. In fact, when the system was created, that was the number given to the brightest of all stars.

Over the centuries, though, astronomers stopped assigning magnitudes based on observations with the eye alone. They used photographs, then sensitive light detectors, to precisely measure the brightness of a star. So four stars were assigned magnitudes that were negative numbers, led by Sirius at about minus 1.4.

The magnitudes of the planets vary as our distance from them changes. Right now, for example, Jupiter is at minus two. But at its peak, it reaches minus 2.8. And Mercury varies even more. Right now, it’s near its best — shining at magnitude zero, close to the Moon tomorrow morning.

Script by Damond Benningfield

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