Sunspot
Sunspots are temporary phenomena on the Sun’s photosphere that appear as spots darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic field flux that inhibit convection. Sunspots usually appear in pairs of opposite magnetic polarity. Their number varies according to the approximately 11-year solar cycle.
Individual sunspots or groups of sunspots may last anywhere from a few days to a few months, but eventually decay. Sunspots expand and contract as they move across the surface of the Sun, with diameters ranging from 16 km (10 mi) to 160,000 km (100,000 mi). The larger variety are visible from Earth without the aid of a telescope. They may travel at relative speeds, or proper motions, of a few hundred meters per second when they first emerge.
Indicating intense magnetic activity, sunspots accompany secondary phenomena such as coronal loops, prominences, and reconnection events. Most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings.
- source
- images: NASA/SDO/SOHO/JAXA
(via astronomyblog)
Craters on Moon:
1° From crater Theophilus (100km diameter) below to crater Langrenus above.
2° From bottom to top, dark titanium rich lava in the Sea of Fertility then the diamond shaped patch is the Marsh of Sleep. Small bright crater Proclus is thought to be a recent impact crater and has thrown out bright ejecta that is much lighter than the surrounding ancient weathered rock. Above is the rather hexagonal Mare Crisium.
3° From the Sinus Iridium top left through the Mare Imbrium with the Alpine Valley in the centre. (This original image is horizontal)
4° At the middle and bottom of this image, sunlight is shining on a mountain peak in the Alexander crater which lies beyond the day/night terminator.
Image credit: John Purvis
(via astronomyblog)
