If you look towards the west after sunset you cannot miss the planets Venus and Jupiter, as they shine so bright even during twilight. Known as the ‘Evening Star’, the planet Venus is a tantalising celestial beacon even for casual star gazers due to its brightness. This is because Venus has the highest reflectivity (albedo) of any planet within the solar system.
Venus is so bright since it is blanketed with clouds which reflect over 70 per cent of sunlight striking it.
Jupiter is now less bright as it moves away from the Earth.
The moon, for instance has a much lower albedo, reflecting only around 10 per cent of sun-light received. This is because it has no cloud cover (having no atmosphere) and is made up of volcanic rock.
It appears so bright from the Earth only because it is much closer to us than any other celestial object.
The brightness of Venus makes it notoriously difficult to observe, however.
The planet is shrouded in reflective clouds containing sulphuric acid that appear bright but featureless at the eyepiece. Still, careful imaging with filters, as used in these composite images, can reveal subtle cloud patterns.
This spring’s evening apparition of Venus is the best one for observers in Malta and others in the northern hemisphere for the past seven years.
It will ultimately end with Venus transiting over the surface of the sun (as seen from the Earth, of course), the last one to occur in our lifetimes, on June 6.
It is good to observe Venus – but from a distance. Its atmosphere is nearly comp-letely made up of carbon dioxide (with around 5% nitrogen) and is clear until the sulphuric acid cloud layer starts about 50 km above the surface.
The atmospheric pressure is about 90 times that of the Earth at the surface and a runaway greenhouse effect has over the millennia raised the surface temperature of Venus to around 500°C – more than that of Mercury and hot enough to melt tin and lead.
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Architect Alexei Pace is president of the Astronomical Society of Malta.