Transit of Venus

Inside the orbit of the Earth lie two planets, Venus and Mercury. When either planet passes between the Earth and the Sun it is called "inferior conjunction". Potentially both these planets can pass exactly between the Earth and the Sun -- their tiny disks appearing to move across the Sun's face. However, neither planet has an orbit that lies in the plane of the Earth's. Since the orbital planes Venus and Mercury are tilted over at an angle, they appear to pass either above or below the Sun at inferior conjunction. Transits of Venus across the disk of the Sun are among the rarest of planetary alignments. There are only about 12 per millennium! Indeed, only six such events have occurred since the invention of the telescope (1631, 1639, 1761, 1769, 1874 and 1882). No transit of Venus occurred in the last century. The next two transits of Venus will occur on 08 June 2004 and 06 June 2012. We are quite lucky that two transits are going to happen in the next few years. Transits of Venus are only possible during early December and early June when the orbital nodes of Venus pass across the Sun. If Venus reaches inferior conjunction at this time, a transit will occur. Transits show a clear pattern of recurrence at intervals of 8, 121.5, 8 and 105.5 years. The next pair of Venus transits will occur over a century from now on 11 Dec 2117 and 8 Dec 2125. The planet Mercury can also transit the Sun. Since Mercury orbits the Sun more quickly than does Venus, it undergoes transits much more frequently. There are about 13 or 14 transits of Mercury each century. All Mercury transits fall within several days of 8 May and 10 November. The last transit of Mercury occurred on 7 May 2003, and the next will occur on 8 Nov 2006. Transit of Venus, 8 June 2004 (afternoon) On 8 June 2004 the planet Venus will cross the Sun's disk as seen from Earth. It will cut into the solar disk at about 1:13 p.m. in the afternoon and will pass off the other limb at about 7:25 p.m. (after sunset in Singapore). The last occasion on which this happened was 1882, over a century ago. The entire transit will be visible in Asia except the extreme eastern portion, and most of the Indian Ocean. Details of the transit are as follows: Phases Singapore local time Ingress, exterior contact 8 June 2004 13h 13m 30s Ingress, interior contact 13h 32m 47s Lease angular distance 16h 19m 41s Egress, interior contact 19h 06m 35s Egress, exterior contact 19h 25m 51s (after sunset in Singapore) Note: Proper solar filter would be required to view the transit. Looking directly at the Sun without proper solar filter or protection would cause permanent blindness. Always be sure to use the proper optical filters to protect your eyes. Never look directly through a telescope towards the Sun, even with filters (only professionals well versed in these matters may do so)! You may view the Sun directly only through a special filter made for safe solar viewing. If you are not certain that a filter is approved and safe or you have any other doubts - DO NOT USE IT. The safest way to view the Sun is indirectly using a projection method. Projection of the Sun onto card is by far the safest method. Even a modest telescope will show Venus. A transit of Venus is like a solar eclipse, but instead of the Moon being in line between the Earth and Sun it is the planet Venus. You can hardly fail to notice a solar eclipse because the Moon, being about the same apparent size as the Sun, blocks out its light. Venus, on the other hand, looks very much smaller from Earth and so you would have to be specifically observing the Sun to see the small disc of Venus passing across its disk. Solar eclipses occur every year or so somewhere on Earth, but you could have been observing the Sun for the last century and still not have seen a transit of Venus. Venus appears very small (Venus is only about 58'' and the Sun is about 1891'') as seen from Earth, so as it passes across the Sun, it will be just big enough to be seen without any magnification with the unaided eye through a solar filter. Using image projection onto a card will also show the planet's slow progress but perhaps a little to set up in says, a school playground. To observe the transit you will need either a pair of binoculars or a small telescope, two pieces of white card and some kind of photographic tripod (a solid chair will do). With one of the pieces of card cut one hole in the centre if you have a telescope or two holes if you have binoculars for the eyepieces. Push the card onto the telescope or binoculars and fix with masking tape (sellotape is okay but it is transparent). On binoculars, block one of the eyepieces with a lens cap. Mount the binoculars or small telescope onto the tripod and fix them in such a way that they can be pointed into the sky towards the Sun. Get someone to hold the other piece of white card a short distance away from the eye piece (as shown in the drawing below). Slacken the mounting so that you can move the telescope with ease until the 'smallest shadow' has been achieved onto the white card. Do not under any circumstances try to align the binoculars or telescope with the Sun, by looking through them. At no time during the transit should the apparatus be left unattended - blindness is no fun and the damage cannot be undone! During the six-hour transit you will have to move the set up in order to follow the Sun. However, because you are using a small telescope or binoculars you will find several minutes of comfortable viewing before the apparatus has to be reset. For those who do not own a tripod, a high backed wooden chair is also ideal, but following the Sun may prove a little tricky. Of course, if you have a nice sharp image you can use a camera over the edge of the masking card to capture images of the transit as it progresses. For a larger image, please click here. Transit images obtained using the QUESTAR 7 telescope at the Singapore Science Centre Observatory.