The Return of Venus (January)

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    The Return of Venus

    by Paul Downing

    SOUNDS
    like the title of a romantic novel, doesn’t it? However, this is definitely
    astronomy. Has anyone noticed the bright star that has suddenly appeared in the
    evening sky after sunset? If you look
    just after sunset as the sky is darkening you will see it, and you may be
    surprised to learn this is not a star at all but the planet Venus.

    About
    the same size as Earth, Venus is our nearest neighbour in space apart from the
    moon, and at times, when our orbits around the sun bring us close to each other
    it can be "only" 41 million kilometres away. Right now, though, it is
    almost as far away from us as it can get – approximately 250 million kilometres.
    This is because it has just become visible in our night sky as its orbit brings
    it around the far side of the sun from us.
    As the weeks go by you will see this "new star" rise higher
    and higher in the sky after sunset. It will also become even brighter, mostly
    because it is getting closer to us as it chases us in our own orbit around the
    sun.

    By
    late May it will be as high in our night sky as it ever gets because it reaches
    a position where it is at its maximum apparent distance from the sun. After
    this point it will appear to start moving back towards the sun, sinking quite
    quickly lower and lower until, by late July, it will once again be lost in the
    sun’s glare, to return as a morning star rising before the sun.

    It
    is interesting to note as Venus drops towards the horizon during July it will
    appear significantly larger and a good pair of binoculars, held steady on a
    wall or tripod can show it as a tiny crescent. PLEASE do not attempt this until
    the sun has properly set for fear of accidentally looking at the sun through
    the binoculars. You can easily be blinded for life in a second.

    Venus
    is so bright because its surface is completely covered by thick, white clouds
    which reflect back into space a large proportion of the sunlight falling on
    them. We say that its albedo is very high. The clouds
    consist of corrosive sulphuric acid vapour and other nasty things and surface
    temperatures are high enough to melt lead due to a runaway greenhouse effect. So
    why does Venus show phases, like the moon? To understand this I have attached a
    diagram for you which demonstrates how the phases are
    produced. You can conduct an interesting experiment in your own kitchen to see
    how this works, using a torch and two round objects (representing the Earth and
    Venus). Venus and Mercury are the only two planets to show phases because they
    orbit inside our own path around the sun. All the other planets orbit further
    out than we do and so do not show significant phases.

    This article was printed in January 2007

    Send your astronomy questions to [email protected]

    Also
    see www.paulandliz.org

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