The night sky in December

The sun’s heat may be felt less than during the summer months, it is in the sky for a longer time and at a higher altitude. However, irrespective of the movements of the Earth, the sun’s surface keeps changing due to the colossal reactions taking place inside it.

The sun’s photosphere has thousands of bumps called granules and usually a few dark depressions called sunspots. Each of the numerous granules seen in the accompanying photo, shot last month by Leonard Ellul Mercer, is the size of Earth, but much shorter-lived.

A granule slowly changes its shape over an hour, and can even completely disappear. Hot hydrogen gas rises in the bright centre of a granule, and falls back into the sun along a dark granule edge. These photos allow students and solar scientists to study how granules and sunspots evolve as well as how magnetic sunspot regions produce powerful solar flares.

The image also shows long filaments which cross part of the sun. The filaments are actually relatively cool and dark prominences of solar plasma held up by the sun’s magnetic field, but seen against the face of the sun. Filaments typically last a few weeks before falling back. It would take around ten Earths, set end-to-end, to match the length of one of the filaments.

For up-to-date information join the Astronomical Society of Malta’s group on Facebook.

Architect Alexei Pace is president of the Astronomical Society of Malta; e-mail: info@maltastro.org.

Astronomical events this month

Wednesday: Maximum Geminid meteor shower (bright moon will hamper observations).
Next Sunday: Last Quarter Moon – one-half of the moon appears illuminated by direct sunlight while the illuminated part is decreasing.
December 24: New Moon – The moon is not illuminated by direct sunlight.
December 27: Moon near Venus (evening sky).