Venus is high and bright in our evening sky, and on the
afternoon of June 5th, will give us, quite literally, the chance of
a lifetime, the opportunity to observe the last transit of the planet across
the face of the Sun for 105 years.
The society is
planning to observe this event, hopefully with a solar telescope, the purchase
of which we are fund raising for at the moment. Any donations welcome. We are
planning a BBQ two days after the March meeting. The meeting is scheduled for
Thursday 22nd March, and the BBQ on Saturday 24th at
Georgetown Villas on 7 mile beach. Details and ticket purchase availability
will be sent later.
especially high and bright in the evening sky every 8 years, this year
included. For every 8 orbits Earth completes around the Sun, Venus completes
Late in March,
Venus reaches its greatest elongation, the farthest distance it will be
from the Sun in the sky as seen from Earth. This year the angular distance will
be 46°, or about four-and-a-half fist widths.
The planets orbit the Sun in roughly
the same plane, which means that, if you were to look at the solar system from
the side, the planets’ paths aren’t tilted much compared to each other. Every
year around this time the line drawn in the Northern Hemisphere’s evening sky
by Earth’s orbital plane, called the ecliptic, makes its widest angle with the
horizon, tracing a curve high on the sky. And since the ecliptic is basically
what Venus follows, too, it'll be moving up and down the sky the same way. So,
not only is Venus at its largest angular distance from the Sun, that separation
points nearly straight up.
after the Goddess of Love) is the planet second closest to the Sun, and the
hottest planet in the Solar System. From looking at most of the facts, Venus
initially appears to be very similar to Earth. The reality is, however, very
different. It might be just 652 km thinner, have similar composition, mass and
position, but for a start, Venus' surface temperature is a scorching 484°C,
secondly it is thought to be completely lifeless, and thirdly its surface
pressure is akin to that of an ocean bed (92 times that of Earth at sea level)
- a pressure high enough to pulverize and crush Venus' surface rocks.
All of these major
features stem from one key difference to the Earth - Venus has no water. This
explain Venus' very dense (mainly Carbon Dioxide) atmosphere - here on Earth
the water of the oceans removes CO2 from our atmosphere and keeps
our planet in a state such that we can live on it (in fact the same quantity of
Carbon Dioxide has come out of the Earth's interior as is in Venus'
atmosphere!). In Venus however there is no water to absorb the CO2
and so the atmosphere thickens and produces a runaway greenhouse effect, so the
rays (and heat) of the Sun shine onto the planet and are then trapped there by
the dense atmosphere. In fact, it is very likely that at one point Venus did
have water on it, but because Venus is about 50 million km closer to the Sun
than the Earth is (two thirds of the way between the Sun and Earth) any
remnants of this water have long since evaporated.
atmosphere makes it very hard for us to see the actual surface of the planet.
The first ideas of what the planet may look like came in the 1960s when we were
able to see through the clouds, albeit in quite a primitive fashion, with radar
imaging from ground-based telescopes. However, global scale radar mapping of Venus'
surface did not start until the Pioneer space probe arrived at Venus in
1978-80, and mapped many of its basic surface features. These were followed by
the Soviet Veneras 15 and 16 but it wasn't really until the Magellan Orbiter
arrived in 1992 that we really got a good idea of what Venus was like.
When the data from
the Magellan mission did come through though, it surprised many scientists, as
there were only a tenth the amount of craters that would be expected had Venus
been as old as we thought it was, and the ones which were there were all found
to be relatively fresh. There are now two theories for this - one is that
volcanic eruptions destroy craters as fast as they are made so there will
always be a constant number of craters on Venus, and the other is that 500
million years or so ago, volcanic eruptions resurfaced the planet, destroying
all previous craters. Another thing these space probes found was that at least
85% of Venus is covered by volcanic rock. These are mostly from lava flows and
form the planet's vast plains.
unmistakable in the evening sky, so look up and enjoy.