<p>The time it takes for the Sun to complete one orbit around the center of the Galaxy is called a <a href="https://en.wikipedia.org/wiki/Galactic_year" rel="nofollow noreferrer">Galactic year</a>. It is estimated to last 225 to 250 million terrestrial years.</p>
<p>Now if you know the speed of the Sun in the Galaxy and you know how far the Sun is from the center, you can estimate this period. Let's assume a circular orbit and ignore the (large) error bars, for the sake of simplicity. The Sun is roughly <span class="math-container">$8\,200$</span> parsecs away from the Galactic center. So the circumference of the Sun's orbit is <span class="math-container">$8\,200 \cdot 2 \cdot \pi = 52\,000 {\rm \,parsecs}$</span>. You mention the speed of the Sun is <span class="math-container">$2.1\cdot 10^{-4} {\rm \,parsec/year}$</span>. So to complete one orbit, it takes circumference/speed = <span class="math-container">$52\,000 / 2.1\cdot 10^{-4} = 245 \cdot   10^6 {\rm years}$</span>, that is 245 million years. Pretty close to the actual value!</p>

CC BY-SA 4.0
2020-03-05T13:45:39.973Z
The 'actual value' is calculated not more complex than you show. Just the uncertainty in radial distance speed gives the uncertainty
planetmaker
CC BY-SA 4.0
2021-04-07T12:04:59.500Z
This is fine for a ballpark figure, but the Sun's orbit is not a circle. Perhaps you could address how circular it is and how inaccurate that might make your estimate?
ProfRob
CC BY-SA 4.0
2020-03-05T09:36:55.980Z
2021-04-07T10:28:38.810Z
2021-04-07T10:28:38.810Z
usernumber
<p>We know the speed that the sun travels around the galaxy is <span class="math-container">$220\, {\rm km/s} = 0.00021 \, {\rm parsec/year}$</span>. I'm unsure of how to find the period?</p>

CC BY-SA 4.0
2020-03-05T02:17:33.773Z
Find the distance of the Sun from the Galactic Center and then, assuming a circular orbit, find the circumference...
astrosnapper
CC BY-SA 4.0
2020-03-05T07:14:42.037Z
or the value is easily found by searching for https://www.google.com/search?q=how+long+it+takes+for+the+sun+to+complete+one+orbit+around+the+galaxy%3F&oq=how+long+it+takes+for+the+sun+to+complete+one+orbit+around+the+galaxy
James K
<the-sun><milky-way>
Calculate how long it takes for the sun to complete one orbit around the galaxy?
user32018
# Calculate how long it takes for the sun to complete one orbit around the galaxy?

(Asked by: username_0 on 2020-03-05)

We know the speed that the sun travels around the galaxy is $220\, {\rm km/s} = 0.00021 \, {\rm parsec/year}$. I'm unsure of how to find the period?

**Tags:** the-sun, milky-way
> **Comments:**
> **username_1**: Find the distance of the Sun from the Galactic Center and then, assuming a circular orbit, find the circumference...  
> **username_2**: or the value is easily found by searching for https://www.google.com/search?q=how+long+it+takes+for+the+sun+to+complete+one+orbit+around+the+galaxy%3F&oq=how+long+it+takes+for+the+sun+to+complete+one+orbit+around+the+galaxy  

---

## 1 answers

### Answer by username_3 on 2020-03-05. Score: 4

The time it takes for the Sun to complete one orbit around the center of the Galaxy is called a [Galactic year](https://en.wikipedia.org/wiki/Galactic_year). It is estimated to last 225 to 250 million terrestrial years.

Now if you know the speed of the Sun in the Galaxy and you know how far the Sun is from the center, you can estimate this period. Let's assume a circular orbit and ignore the (large) error bars, for the sake of simplicity. The Sun is roughly $8\,200$ parsecs away from the Galactic center. So the circumference of the Sun's orbit is $8\,200 \cdot 2 \cdot \pi = 52\,000 {\rm \,parsecs}$. You mention the speed of the Sun is $2.1\cdot 10^{-4} {\rm \,parsec/year}$. So to complete one orbit, it takes circumference/speed = $52\,000 / 2.1\cdot 10^{-4} = 245 \cdot 10^6 {\rm years}$, that is 245 million years. Pretty close to the actual value!

> **Comments:**
> **username_4**: The 'actual value' is calculated not more complex than you show. Just the uncertainty in radial distance speed gives the uncertainty  
> **username_5**: This is fine for a ballpark figure, but the Sun's orbit is not a circle. Perhaps you could address how circular it is and how inaccurate that might make your estimate?  

---

