How old is the Sun in Galactic years?

The Moon goes around the Earth, the Earth goes around the Sun, and the Sun goes around the center of the Milky Way. We know the Moon takes about 4 weeks to make its trip around the Earth, and that causes the Moon phases:

We also know that the Earth takes one year to go around the Sun, and that causes the seasons:

We also know that the Earth has been around for about 4.5 billion years, which means it has gone around the Sun about 4.5 billion times. Well, now I ask the question(s):

How long does it take the Sun to go around the Milky Way? How many times has it done that so far, and how many times will this happen before the Sun finally dies?

Well, we know that we travel in (roughly) a circle around the center of the Milky Way, and that our radius from the center is about 8 kiloparsecs, or roughly 26,000 light years. That means our Solar System (including the Sun) needs to travel a distance of 1.55 x 1018 kilometers to go around the Milky Way once. If we know how fast the Sun is moving, we can figure out how long a Galactic Year is. Well, we can both measure and calculate its velocity to be 220 kilometers/second, and so we can just do the math, knowing that there are 31,556,952 seconds in a Gregorian Year, and we find that it takes about 223 million years to make one galactic year.

So, if the Sun is 4.5 billion years old, that makes it about 20 galactic years old. If the Sun has a total lifetime of around 10 billion years, then it has a total galactic age of around 42 galactic years.

What? Did I just say the answer is 42?! Well, this means that one possible question is “What is the Sun’s lifetime in Galactic Years?”


  1. #1 ethan
    March 2, 2008

    Wow! My article has just been roughly translated into Dutch! Look at these new words! Milky Way = Melkweg. Galactic years = galactische jaren. miljard jaar oud = million years old! lichtjaar = light year! This is awesome, Zal de Zon; thanks for bringing this to a new part of the world!

  2. #2 shirley
    March 13, 2008

    good stuff here…please put me on mailing list.

  3. #3 ethan
    March 13, 2008


    If you want on whatever list I have, just register by going to the link under the heading “Meta” on the right!


  4. #4 CODY
    March 27, 2008

    its a a nice site

  5. #5 Joe blow
    October 2, 2008

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  6. #6 Mark
    United States
    January 3, 2014

    So, if the sun (4.5 billion years old) has gone around the galactic center 20 times in its life and we know that the galaxy is around 13.2 billion years old, that means that the galaxy hasn’t really “spun” that many times. The earlier back one looks, it must have been more dense at it’s center before the galactic arms took their present shape. And surely it would have spun faster the further back one looks. But in the big picture, and in a different time frame, it hasn’t spun all that much. Kind of like a spark being flung from a fire.

  7. #7 isacsanthakumar
    October 20, 2014

    14 billion years back Big Bang occured.How was it arrived at?The Galactic year is applicable to the Milky way.Can it be made applicable to the entire Universe?

  8. #8 isacsanthakumar
    October 20, 2014

    The Galactic year is applicable to the Milky way only.It is not applicable to the entire Universe,with innumerable Galaxies.If so,how can we say that the Big Bang occurred 14 billion years back.How was it arrived at?

  9. #9 Wow
    October 20, 2014

    By projecting the trajectory and speeds of the contents of the universe to see what they do.

    And they end up at the same spot around 14 billion years ago.

    Not one jot of “galactic years” is required there, any more than Brhama Years are required. But you can state how long ago the universe began in Brahma years (nearly 2).

  10. #10 jim henderson
    April 23, 2015

    Are there “seasons” in the cosmic year? Can we see a difference when we are on one “side” of the galaxy from the other side? Does the ecliptic ever change? Does the plane of our solar system (and others recently discovered) lie in the same plane as the galactic arms of the Milky Way?

  11. #11 Vuma Theodore Mkhize
    Jhb South Africa
    October 16, 2015

    Interesting …but I’m left with a question now. If the moon orbits the earth & the earth orbits around the sun & so does the sun around the galactic center then does the galaxy orbit around the big bang (the birth of space-time) or the center of the universe?
    Did the birth place of space-time develop gravity later at some point after it occured.