The Transit of Venus, 6 June 2012
Transits occur when a planet crosses the face of the Sun as seen from Earth. Naturally, a planet has to be between Earth and the Sun for this to happen, and so transits are limited to Mercury and Venus. As the orbits of these planets are tilted with respect to Earths orbit, we will see Mercury and Venus cross the Suns face rarely, as most of the time the planets will cross above or below the Sun. Transits can only be seen when the planet is between the Earth and the Sun at the same time as the planet is crossing the plane of Earths orbit. For Mercury, this occurs roughly 13 to 14 times a century, and for Venus, roughly every 100 years. Venus transits occur in pairs 8 years apart. The first transit in this pairing was on 8 June 2004. If you miss this one, the next ones will be in 2117 and 2125! So transits are relatively rare phenomenon, and quite interesting to watch. More information can be found at the sites in the links section.
The simplest and safest way to observe this event is by making a pinhole in a stiff square of cardboard and projecting the image of the Sun onto a flat surface. You are basically making a simple pinhole camera, which will reveal the changes to the Suns outline quite satisfactorily. A card with a 1 mm hole should be projected onto a surface (eg white paper, or a white wall) about 20 cm away, a 5 mm hole should be projected onto a surface 1 to 1.5 meters away. You need to create a reasonable sized image to see Venus, so you need a fair distance between the pinhole and the surface you project the image on. This will mean the image is going to be fairly dim, so you also need some sort of sun shield to keep in image in shadow. I use the longest available postpac postal tube, with alfoil over the top, and wide ring of stiff cardboard to ensure that the image of the sun is projected into a dark area. This link will show you several methods to make pinhole projection systems. This link will show you how to make safe solar viewing and telescope projection systems.
Acceptable filters are specially coated filters that may be purchased from Astronomy suppliers (such as the premade Solar Eclipse viewing glasses or special filter material you can cut to size yourself), or number 14 welders filters. Again, these should be used with special care so as not to expose your eyes directly to the sun by accident. However, Venus will be quite a small dot on the face of the Sun when unmagnified, and it won't look particularly spectacular.
If you have a pair of binoculars, and you are not afraid to expose them to the heat of the Sun, then try making a binocular projection system. I have used this on an old pair of binoculars several times, and they are fine, and produced good views of the transit of Mercury and a partial eclipse, but it's probably a bad idea to use it on very expensive binoculars, as there is a small but real chance the heat will crack the lenses or mess with the coatings. You will need to have your binoculars mounted on a tripod for stability, many modern binoculars come with an attachment point for tripods.
If you have a telescope, use either the special telescope apature filters, or the much cheaper telescope projection system as described in the above link.
Telescopic or binocular projection viewers should look for the black drop effect. This is when Venus is just crossing into the sun, and it looks as if there is a trail or drop joining Venus to the Suns edge.
Photographing the transit is easy if you are using a projection system, just point your camera at the projected image and click. For more complicated photography, see the Sky&Telescope magazine site, or the Transit photograhy site on photographing the transit.
As well, you can use any number of devices designed to attach modern digital cameras or iPhones to a telescope. These can be bought from most optical stores. Definitely practise setting up you projection systems and your photography before hand, rather than trying to sort it all out on the day. There are a few sunspots about, so you should get good images of those.
Alternatively, you might be able to go to one of the local observatories or planetariums that are putting on public viewings of the transits. One such is Sydney Observatory. Or you local astronomy club may be having a public viewing. See the links section for listed public viewings, clubs and planetariums near you. The weather, as always, can be unfavorable, check the Australian Meteorology site for local forecasts. If it rains or is cloudy, try one of the live Webcasts instead.
Schools might like to particiate in a transit measuring exercise. Schools in the nothern hemisphere and southern hemisphere are measuring the transit contact times to calculate the distance from the earth to the Sun. If you haven't already been alerted to this by the Astronomical Society of Australia, you might like to participate. Contact the ASA via the links below or email the groups directly. One group is being coordinated by Arkan Simaan, a physics teacher at a French High School. Contact him via email at email@example.com. Another group is being co-ordinated by Dr Robert Walsh (firstname.lastname@example.org) of the Centre for Astrophysics, University of Central Lancashire, UK. Here is another way you can help astronomers collect transit data.
Remember, do NOT look directly at the Sun, as irrepairable eye damage or blindness can occur. Use only indirect projection (preferable) or Astronomical grade filters (use extreme care).
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Created: Sunday, 23 May 2012, 11:22:32
Last Updated: Sunday, 3 June 2012, 11:22:32