# Homework Help: Calculating Solar Rotation

1. Mar 12, 2014

### magnanimousto

1. The problem statement, all variables and given/known data
Calculating solar of the sun through observing sunspots. We are given a series of photos of the sun over a period of time where we can see sun spots.

I am assuming the way to calculate would be to work out the longitudinal angles of the sun spots in the different photos and then use Angular Displacement to figure it out. The problem is I have no idea how to calculate longitude, or how to get the longitudinal values into something I can plug into the Angular Displacement equation.

2. Relevant equations

from what I understand θ=s/r. θ= ωt. But I have no idea how to use the data to get quantities I can plug in to this.

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2. Mar 12, 2014

### Staff: Mentor

Did you draw a sketch?

For a given latitude and longitude, can you determine where you would see a sunspot? Then you just have to reverse the direction of the calculation.

3. Mar 12, 2014

### magnanimousto

sketch it out like this you mean? how would I find the quantative values from this?

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4. Mar 12, 2014

### Staff: Mentor

What data accompanies each observation? Presumably a time stamp of some form, but anything else? What's the timeframe for the whole series?

The reason I ask is that the Sun's rotational axis actually has a tilt (inclination) of about 7.5° to the ecliptic, so the time of year when the snapshot is taken, presuming an Earth-based platform for capturing the photos, will influence the apparent latitude -- spots won't track horizontally unless the viewing position has the rotation axis vertical and is located in the plane of the Sun's equator.

5. Mar 12, 2014

### Staff: Mentor

That's not the direction I had in mind, but it can be useful as well.
Well first you have to find the position in the image (like x,y-coordinates), and afterwards you have to translate this to a position on the actual (curved) surface of sun.

@gneill: I guess we can neglect this here.

6. Mar 12, 2014

### Staff: Mentor

Could be. I can't tell the course level that the question pertains to from the given info, that's why I threw that out to see what the response might be. Carry on....

7. Mar 12, 2014

### magnanimousto

OK I get it. Thanks guys. I use the measurement of the x,y co-ordinates and then sin(inverse) to find angle. Then calculate difference in angle between the two spots per difference in time which would give me the angular velocity.