Sidereal period

[Kabi]

Hello all

In the last half year my son and I still used our trusty binocular and the Celestron Travelscope 70 on a very wobbly tripod to learn the sky. With the lack of dark skies this summer, we switched to looking at the sun (using a DIY filter using Baader Solar film) and yes, you can see the sun in Scotland, sometimes… We really got fascinated by observing sunspots.

We started to sketch the positions, but changed to make short movies from the sun and learned how to stack them into pictures. |We thought we could then follow the sunspots and calculate the solar rotation. There are some great tutorials out there, BUT they use photos taken with professional equipment. Not our shaky photos and not knowing were the poles are….

So, we had to align the photos by first resizing the disc to be the same size on each photo. We assumed that the poles are along the edge of the disc and opposite of each other ;-) We know that the first might not be true, but close enough!

Then we used the photos furthest apart in time and drew straight lines between the same two sunspots. All lines (at different latitudes) needed to be parallel assuming the sunspots moved along the same latitude. Again close enough.

Figure shows two layers (i.e. photos). Alignments is not quite there yet.

 

Better!

We then picked the x,y coordinates and used some trigonometry not the grid lines) and calculated the latitude and longitude  of the sunspots and together with the timing of the photos we could calculate their angular speeds.

There was a little hiccup when the period looks a bit long, but we then finally calculated the sidereal period as well. Our best estimate is now 25.3 days for the sidereal period, give or take one day at a latitude of 11 degrees.

Well, not proper scientific quality and more of a student project, but loads of fun anyway.

Best thing though is that I can proof to my wife that every money spent on astronomy kit is money well spent on the education of our kids.... ;-)

So, we are hunting for a better tripod now!

Regards,

Lars

[Floater]

That is excellent! Great to hear of you and your sone working together on the project.

Keep up the good work.

[Steve Ward]

Great work ... 

Bear in mind that the Sun rotates a different speeds at different latitudes , in case you start getting strange answers to your calculations .

[Kabi]

Great work ... 

Bear in mind that the Sun rotates a different speeds at different latitudes , in case you start getting strange answers to your calculations .

Yes, Steve. We start to see an increase in the speed towards the poles. Need more tracked sunspots though and the weather is not the best at the moment...

[Steve Ward]

The speed is greater at the Equator and decreases as the latitude increases .

Looking at the disc you might have a bit of a wait until the next sunspot , this year has been much quieter than last year ... 

[laudropb]

Very nice project. Thanks for posting.

[Kabi]

The speed is greater at the Equator and decreases as the latitude increases .

Looking at the disc you might have a bit of a wait until the next sunspot , this year has been much quieter than last year ... 

Doh. Meant to write "increase in the period"!

The slowest sunspot we measured seemed to take about 30 days to get around. But we haven't followed one close to the poles that would introduce more errors as well.