The Transit of Venus, 8 June 2004

On Tuesday, 8 June 2004, Australians will have a rare opportunity to view a transit of Venus. This will be the first time to view one since 1882. A transit of Venus played an important role in Australian history, as a certain Captain James Cook mapped the East Coast of Australia after observing a Transit of Venus in 1769.

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. If you miss this one, the next will be in 7 June 2012. The following transits are 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 best 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, 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, as Venus will be quite a small dot when unmagnified, it will be difficult to see anything.

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. 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 you camera at the projected inage and click. For more complicated photography, see the Sky&Telescope magazine site, or the Transit photograhy site on photographing the transit.

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 arkan.simaan@free.fr. Another group is being co-ordinated by Dr Robert Walsh (rwwalsh@uclan.ac.uk) of the Centre for Astrophysics, University of Central Lancashire, UK.

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).

• Make your own pinhole projection systems
• Make your own binocular projection system for safe viewing of transits and sunspots.
• More links for safe solar viewing and telescope projection systems.
• Astronomical Society of Australia Fact Sheet.
• Astronomical Society of NSW page on the transit
• A good Australian Amateur site on viewing the transit and telescope projection systems
• More information on the transit from an Australian prespective.
• Extensive information at SunEarth on the transit
• Photographing the transit.
• Sky&Telescope magazine, on the transit. Various links and how to photograph the transit.
• BBC site on the Transit.
• A NASA site with a history of James Cook's Venus expedition
• Simultaneous transit of Venus and the International Space station
• Venus in the SOHO LASCO C3 camera (try the animations, they are large though)
• My report on the transit of Mercury in 2003.

• ABC online science and the transit (with webcam listings)
• Catalyst on the transit (brief)
• Science Show Saturday June 5, interview with Duncan Steele (from Adelaide) on preparing for the transit

• Public viewing of the transit at Sydney Observatory.
• Public viewing of Transit at Victoria's Science Works Museum and Planetarium

• Live webcam feed from Perth Observatory
• Live Webcam from CSIRO
• NASA's SunEarth site with a live webcam
• Space weather has a list of even more webcams

• OnLine Astronomical Societies in Australia, from the Astronomical Society of New South Wales Inc.
• Astronomical Society of Australia

• Canberra Planetarium and Observatory
• Launceston Planetarium
• Science Centre and Planetarium (Wollongong)
• Sir Thomas Brisbane Planetarium
• Perth Observatory and Planetarium
• Museum of Victoria Planetarium, Skynotes Index

• Australian weather forecasts