Aldebaran

Remember back in 2006 when poor, old planet Pluto was demoted? A group of scientists decided that there are three main categories of objects in our solar system:
Planets: 8 from Mercury to Neptune.
Dwarf Planets: Pluto and any other round object that “has not cleared the neighborhood around its orbit, and is not a satellite.”
Small Solar System Bodies: All other objects orbiting the Sun.

plutoI felt bad – and so did a lot of other Earthlings – for Pluto.

This past week I read that the waxing gibbous moon outside my window was moving toward the star Aldebaran, the brightest star in the constellation Taurus the Bull. Nothing odd about that. Normal movement.

But what I had not known was that Aldebaran also had a kind of demotion. It used to be the North Star, also known as the Pole Star. How does a star lose its rather prominent name in the sky?

You probably learned that Polaris is the North Star, but a long time ago Aldebaran had that honor. That was 450,000 years ago.

Back then, it appeared several times brighter in the sky then than it does now. In a way, it shared the title because it was very close to another very bright star, Capella, so they served as a double pole star. (This was 447,891 BCE, if you like precision.)

That’s pretty amazing, but it was a long time ago. But what really hit me was that in this little solar system of ours and in our beautiful galaxy and this almost unimaginable universe, everything is always moving.

Even the sky looked different hundreds of thousands of years ago.

sky chart

This illustration shows the view as seen from present-day Arizona in 447,000 B.C., when Aldebaran and Capella served as double pole stars. Illustration via Carina Software and Instruments and earthsky.org

The identity of the pole star shifts over time, due to the 26,000-year cycle of precession. To read more about that, click into this article about Thuban, another former pole star.

Still, how can it be, you might wonder, that the stars Aldebaran and Capella were once so near each other on the sky’s dome? They’re not especially close together now. Aren’t the stars essentially fixed relative to one another? The answer is that, yes, on the scale of human lifespans, the stars are essentially fixed. But the stars are actually moving through space, in orbit around the center of the galaxy.

The Moon is moving across the constellation Taurus and, in the Zodiac, Aldebaran is important. It is part of that merry band of stars in front of which the Sun, Moon, planets, dwarf planets and small solar system bodies dance their rounds.

The Earth is spinning as I sit here typing. It is making the moon and Aldebaran shift westward but the Moon is moving to the east relative to the “fixed” stars because of the Moon’s orbit around us. It is all so amazing. Some people think that looking up into that giant sky makes them feel so small. I disagree. It makes me feel a part of something so enormous and grand.

Hello, Aldebaran. We didn’t forget you.

 

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