The Moon forms a shifting triangle with two bright orange points of light the next few nights. The brighter dot is the planet Mars. The other is the star Aldebaran, the eye of the bull.

Tonight, Mars stands to the lower left of the Moon at nightfall, with Aldebaran farther below the Moon. The triangle will be tighter as the trio sets in the wee hours of the morning.

On the scale that’s been used for centuries, Mars is at a magnitude of about minus 1.2, while Aldebaran is plus point 85. The lower the number, the brighter the object.

When the magnitude scale was devised, it was based on observations with the unaided eye. The brightest stars and planets were magnitude zero. It was hard to judge precise differences in brightness, especially since you can’t see all the stars at the same time.

Telescopes and photographic plates made it easier to measure brightness. So each star and planet could be assigned a precise number. The brightest objects were given negative numbers.

The magnitude of a planet changes as its distance from Earth changes. Earth and Mars are moving apart now, so Mars is fading week by week. If a star’s magnitude changes, it’s because the star itself is changing, or because it has a companion and they stage eclipses. Aldebaran may vary by a tiny bit — but not nearly enough to notice with the eye alone.

The Moon, Mars, and Aldebaran will bunch closer tomorrow night, then move apart by Wednesday.
 

Script by Damond Benningfield

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