Is our Sun stationary?

Posted on December 25, 2007

6


Ask a small child about to enter kindergarten whether the Sun moves and he will say yes. Ask the same question to a young student who has been given some knowledge of astronomy and he will proudly claim that while the Sun is stationary, it is the Earth that moves around it. Ironic as it may be, but in this case the small kid would be right. Of course the Sun moves.

Before all the students who have been taught otherwise rise in protest, it must be made clear that motion, any motion, is relative. As far as the solar system goes, the Sun doesn’t appear to move except for its slow differential rotation. But leave the solar system and this picture changes. The Sun is revolving round the centre of our galaxy, the Milky Way, at almost 220 km/s which means one revolution will take 225 million years. As it revolves, it takes all members of the solar system for the ride with it. Something similar to being in an airplane. The airplane is moving really fast but the passengers inside don’t really feel it.

Apart from this elegant motion in the galaxy, it also oscillates a little with respect to the nearby stars. Interestingly, the Sun is moving 20 km every second towards an imaginary point in the constellation Hercules near the famous star, Vega. That’s right, we are on a trip to Vega! Calculate how much time it would take to reach given that Vega is 27 light years away.

And in fact that is not all. The Milky way is part of what is known as the Local Group of galaxies. All the members are moving relative to each other at 100 km/sec or less due to gravitational interactions. So that’s one more motion of the Sun on a much wider scale!

We can keep moving further out. The satellite known as Cosmic Background Explorer (COBE) has shown that the entire local group is moving at about 600 km/s with respect to a background radiation that exists. Thus nothing in the universe seems stationary and our Sun is no exception. Thanks to gravitational pull, it takes us wherever it goes.

The image displays the background radiation present in the universe. The smooth variation is due to Earth's motion with respect to the background radiation.

 

Tagged: ,