How to calculate the Sun's rotationtime at the equator?

Bram Turismo

Go Flying Lizards!
Premium
10,845
Belgium
Belgium
bramturismo
Hey guys, a little physics or math question to you geniuses.

By hand of the Doppler-effect, I found out that the Sun's speed of rotation is about 2,1 km/s. Now, I know the time of rotation at the Sun's equator is around 25,4 days, but with my calculations, none of my answers are correct.

Information given is my answer to the speed of rotation (which I answered correct, 2.1 km/s) + the radius of the Sun (which is about 6,96.10^8m).

My plan was to get those 2,1 km/s to m/s (first calculate to km/h, then to m/s?), then divide the radius by the calculated km/s...


Someone who could help me with this?


Thanks in advance 👍
 
Yeah, I get there. What you need to do is take the circumfence of the Sun instead of the radius.

With the radius, I got a circumfence of 2 x r x PI = 4,37 x 10^9 meters.

With 2,1 km/s rotation speed, which equals 2100 m/s (x 1000), you need to divide the circumfence by the rotation speed to get the duration of a full rotation:

4,37 x 10^9 meters / 2100 meters a second = 2081371.43 seconds.

Divided by 60 (for minutes), 60 (for hours) and 24 (for days), I get 24,x days, which I consider close enough to 25,4.

EDIT: I just noticed that when you divide meters by meters a second, you don't get seconds, but 1/seconds. But anyway, the result does it I guess.
 
Yeah, I get there. What you need to do is take the circumfence of the Sun instead of the radius.

With the radius, I got a circumfence of 2 x r x PI = 4,37 x 10^9 meters.

With 2,1 km/s rotation speed, which equals 2100 m/s (x 1000), you need to divide the circumfence by the rotation speed to get the duration of a full rotation:

4,37 x 10^9 meters / 2100 meters a second = 2081371.43 seconds.

Divided by 60 (for minutes), 60 (for hours) and 24 (for days), I get 24,x days, which I consider close enough to 25,4.


I always forget about circumfence :dopey:

Thanks 👍

But, I always thought km/s isn't the same as km/h, which can be easy calculated to the basic m/s?
 
By hand of the Doppler-effect, I found out that the Sun's speed of rotation is about 2,1 km/s.

Just think about where the speed is that you've calculated is. If the speed is at the equatorial surface, then you have to figure out how far the equatorial surface has to travel in order for the sun to rotate once. If the speed is at 80 degrees latitude, you're going to get a different answer because the surface doesn't have to go as far to complete a full rotation.
 
I always forget about circumfence :dopey:

Thanks 👍
You're welcome!

But, I always thought km/s isn't the same as km/h, which can be easy calculated to the basic m/s?
Well, they aren't the same.

km/s is kilometers a second
km/h is kilometers an hour
m/s is meters a second

Now, "kilo" simply means 1000, so 1 km/s equals 1000 m/s. So that's easy, because there always is a factor of 1000 in it. It just gets a tad more complicated when we have km/h and need m/s, cause we need to do two conversions. We know that 1 hour equals 3600 seconds though, so km/h times 1000 (= m/h) divided by 3600 equals m/s. That shortens to

km/h / 3,6 = m/s.
 
not to mention that, I believe the different latitiudes of the surface plasma travel at different speeds in themsleves. in a V shape, as is usually indicated for Venus's cloud cover. I'd check with a scientific website to be sure of all this, tho
 
not to mention that, I believe the different latitiudes of the surface plasma travel at different speeds in themsleves. in a V shape, as is usually indicated for Venus's cloud cover. I'd check with a scientific website to be sure of all this, tho

Oh, absolutely. The surface clouds/plasma are not a good reading of planetary/star rotation since they have a relative speed that is sometimes quite substantial. I know that there was a great deal of controversy over Saturn's rotational rate. I believe the matter was settled with magnetic measurements of the rotation of the core.
 
Wow wow guys, don't get that complicated, I'm only 18 :lol:

But thanks though, especially The Interceptor, I think 24 comes close enough :cheers:
 
Back