Transit of Mercury, 9 November 2006

• Obligatory Warning
• What is going on
• When to look
• What to look with
• Links Updated 4-10-2006 with new webcam/webcast sites

Never look at the Sun directly, either with the unaided eye or through telescopes or binoculars; you can permanently destroy your eyesight. If using a telescope, securely cover or remove your telescopes viewfinder. Accidental exposure to the sun through the viewfinder can produce blindness or serious burns. A graphic illustration of what would happen to a human eyeball when exposed to the unfiltered Sun through a telescope is shown here.

Whats going on?

On the morning of Thursday, November 9, Mercury will transit the Sun as seen from Australia, New Zealand and parts of the Pacific, East Asia and the Americas. 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. Our last transit of Mercury was in 2003, but our next observable transit will not be until 2032. So transits are relatively rare phenomenon, and quite interesting to watch.

When to Look

The transit starts around sunrise for the central Pacific and East Asia. In New Zealand, the transit starts well after sunrise, and all of the transit is easily seen. In Australia, the eastern states will see the transit starting just after sunrise, central states will see the sunrise with the transit well underway and in Western Australia the run rises around mid transit. In all Australian cites, the exit of Mercury from the Sun is observable. The table below gives contact times for various cities in local times (daylight saving where appropriate).

First contact is when Mercury first touches the Sun, second contact is when Mercury is fully inside the Sun, but still touching the edge of the Sun's disk. Mid Transit; least angular distance from the centre of the solar disk, Third Contact is the last time entire disk of Mercury is visible against the Sun, Last contact is the last contact with the solar limb.

Remember, do NOT look directly at the Sun, as irrepairable eye damage or blindness can occur. Use only indirect projection (preferable) or Astronomical grade full aperture filters (use extreme care).

What to look with

Do NOT look directly at the Sun! as this can cause blindness or severe burns. Use only safe solar projection methods or full aperture solar filters. Do not use so-called filters such as over exposed film, smoked glass etc. These materials are NOT, repeate NOT safe. Never use eyepiece filters for telescopes. These can crack at inopportune times and destroy your eyesight. If using a telescope, securely cover or remove your telescopes viewfinder. Accidental exposure to the sun through the viewfinder can produce blindness or serious burns.

Ufortunately, Mercury is so small that simple pinhole projection methods, or solar film, will not not reveal it. The best way to observe this event is with a telecope, either using a projection system or a full aperture astronomical solar filter, or high power binoculars. This link will show you how to make safe solar viewing and telescope projection systems. When using all projection systems, be careful to make sure no-one can accidently view raw sunlight.

If you have a pair of binoculars with reasonable magnification, 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 10x50 binoculars several times, and they are fine, and produced reasonable views of the 2003 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.

Do practise with your telescope some days before hand, so you get a feel for setting things up and focussing. Check out the SOHO site for sunspots, and if any are around, use them to test your projection system, focussing arrangements and photography. For telescopes, since you have removed/covered the viewfinder, centering the Sun may be a bit tricky. Look at the telescopes (or binoculars) shadow and move the telescope until the shadow is at its smallest. The Sun will now be in your eyepiece, although you may need to juggle it a bit to centre it. Again, practise this a few days before the transit, so you are not juggling theings around at the last moment.

Telescopic viewers should look for the black drop effect. This is when Mercury is just crossing into the sun, and it looks as if there is a trail or drop joining Mercury 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. It is best to have the camera on a tripod to keep the image as still as possibble. For more complicated photography, see the Transit photography site. This was for the transit of Venus, but is relevant to photographing Mercury as well.

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.

One thing you should not forget when viewing transits, or eclipses of the sun, is to make sure you put on sunscreen! Even if there is a thin haze covering the sun, you can get badly sunburnt, as I did when watching the 2003 traansit of Mercury.

• What would happen to a human eyeball if exposed to the unfiltered Sun through a telescope
• Make your own binocular projection system for safe viewing of transits and sunspots.
• More links for safe solar viewing and telescope projection systems.
• My sticks, cardboard and sticky tape projection system
• ASA transit fact sheet
• Extensive information at SunEarth on the transit
• Photographing transits.
• Simultaneous transit of Venus and the International Space station
• Mercury in the SOHO LASCO C3 camera (try the animations, they are large though)(Note: During the last weeks of September, you are seeing Venus and Mars in the camera, btween 6 and 9 Nov, Mercury enters the field and sweeps past Venus).
• My report on the transit of Mercury in 2003.
• My report on the transit of Venus.

• Public viewing of the transit at Sydney Observatory.

• Paul Floyd's Transit Webcast
• NASA Webcast
• Hawaii Webcast
• Kitt Peak Webcast
• Theodore Lunar Observatory

• 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