Venus Transits the Sun

[Doug L]

... what are the other spots closer to the centre?

Actually, that's what these are called - 'sunspots'. If you google that word you'll get a huge amount of info, but basically they are holes in an outer layer of the sun caused by protruding magnetic field lines. Some small spots disappear after a few hours, but large ones can last for more than a month (longer than one complete rotation of the sun) and can be visible with no optical aid other than a filter in front of your eyes. It's fun watching them with filtered telescopes or binoculars, as they grow and change in shape. The cheapest safe sunspot filter for your eyes or small binoculars is a #14 welders filter. I looked through one of these during the Venus transit and it was thrilling to be able to easily see the dark disk against the sun with just my eyes. General hardware stores may not have filters that dark, so one option is to stack two #7 welding filters (or any combination that adds up to at least 14). The only slight problem with this is that welding filter glass is not precision optical quality and doubling the thickness means resolution will suffer more. Also, I must warn that if you put this, or any other solar filter on binoculars, scopes, etc., do not put it at the eyepiece end (where the sun's light and heat is focused). The filter must completely cover the front (closest to sky) lens before the light enters the optical system.

[Doug L]

... Amazing what one has to do to take images of the sun...

Actually, if one purchases a relatively inexpensive solar filter to cover a 300mm - 500mm lens, anyone can take snapshots of large sunspots. But yes, it can get more complicated, and expensive, if you have to purchase a telescope or more specialized filter systems. Most of the highest resolution shots of the sun, moon and planets these days are shot using webcams instead of regular cameras on the scopes. Processing packages then take the sharpest video frames in the shooting sequence and stack them together into a single image.