Everything Is Always Moving

This photo of Aldebaran is cropped from one made of the Hyades star cluster, the nearest cluster to Earth.

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

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

In 2015, 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 until then 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 and place 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. 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.  The sky looked different hundreds of thousands of years ago.

This illustration shows the view as seen from present-day Arizona in 447,000 BCE 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. This is due to the 26,000-year cycle of precession. (read more)

Most people believe the stars essentially fixed relative to one another. Within the scale of human lifespans, that is true. But stars are moving through space in orbit around the center of the galaxy.

The Earth is spinning as I sit here typing. It is making our 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 night 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.