I Got The Sun In The Morning...

...And all of the rest of the day since I now have an Orion Solar Filter. Simply fit it over the front of the telescope and it cuts out 99.999% of incoming light. This makes the Sun a safe observing target and shows up sunspots, prominences and granulation.

Sunspots are areas on the surface of the Sun where the magnetic field has become tangled up making one patch cooler than the surrounding area. The temperature of the sunspot will be around 4,000 degrees compared to around 6,000 degrees for the surrounding area. The cooler area shows up as dark spot on the surface. Sunspots can be very big - the biggest can be up to around 50,000 miles across.

It has been well publisized that the Sun has been rather quiet over the last few years. The Sun goes through a fairly regular cycle every 11 years or so where it changes from having very few sunspots to lots of sunspots and back again. The current low period has been going on for longer than usual but there are signs that activity is beginning to pick up again (last year 71% of days showed no sunspots compared to 16% so far this year).

This increase in activity left me optimistic that once the recent spell of rain had abated I would be spotting spots straight away. Alas no. The clouds cleared at the start of a mini-streak of 5 spot-free days. This morning was a different story. After consulting the latest space weather, I knew that I'd have at least one sunspot to look at, and here it is:



Sunspot 1101 is clearly visible in the bottom-right quadrant. There was quite a lot of whispy cloud around (as can be seen in the picture) so I settled for a few afocal snaps rather than getting out the webcam. It will be interesting to see what resolution can be achieved on a clearer day and what happens to sunspot 1101 in the future.

Gamma Cassiopeiae

With autumn approaching I felt it was about time to turn my spectroscopic attention to Cassiopeia. The first stellar spectrum I ever observed was that of Gamma Cassiopeiae and 15 years later I couldn't wait to see how it would look through my Star Analyser.

Back in 1866, Gamma Cassiopeiae was the first star ever observed with emission lines in its spectrum. This made it the prototype Gamma Cassiopeiae Variable star, the first known Be star (a type B star with emission lines), and one of the most popular targets for spectroscopy ever since.

One of the most common features of a stellar spectrum is to see hydrogen absorption lines. These are caused by hydrogen atoms in the star absorbing light at a wavelength corresponding to the energy required to excite an electron between different energy levels. For example, the spectrum of Sirius that I posted last month shows a clear H-Beta absorption line caused by exciting electrons between the second and fourth energy levels.

Here are three spectra I took of Gamma Cassiopeiae and instead of absorption lines we can see a clear H-Alpha emission line (in the red part of the spectrum).


Clearly some other process must be taking place. Some of the great minds of the early 20th century found that these emission lines must be coming from material around the star rather than the star itself. This material is a disc produced by a combination of very rapid rotation, magnetic fields and stellar pulsing. The cooling of hydrogen atoms in this disk then produce the emission lines seen in the stellar spectrum.

When I observed this star at university (with considerably better equipment!) I could produce a much more detailed spectrum. It was possible to measure the rotation speed of the disc by calculating the Doppler broadening of the emission line. It was also possible to see a narrower absorption line in the middle of the broad emission line caused by the disk absorbing light from the central star.