by Knut Jørgen Røed Ødegaard and Unni Fuskeland

Since Mercury and Venus orbits inside of the Earth, they will from time to time pass between the Sun and the Earth. Very rarely, they may even line up so that Mercury or Venus passes in front of the solar disc, as seen from the Earth. This is called a transit.

The phenomenon is rather rare - it is 30 years since the last transit of Mercury was visible from Norway and 3 years since the last time on Earth. The transit lasts for over 5 hours, and during this time, Mercury passes slowly across the solar disc.

Mercury is a small planet and so far away that it is tiny compared to the h uge solar disc. We are therefore in need of equipment to observe the phenomenon. NB! Never look at the Sun with binoculars or unprotected eyes. Eclipse glasses may be used to study the Sun, but it will not help seeing the transit of Mercury because Mercury is so small. A reasonable method is to use the projection method with a telescope (see below). Telescopes that magnify 50 to 100 times are recommended.

Mercury about to enter the Solar disc on May 9. 1970. The pictures are taken from Solobservatoriet at Harestua 05:12:42, 05:14:40 and 05:15:59 (CET). Photo: Truls Lynne Hansen et al..


We strongly recommend the projection method with a telescope or binoculars:
Mount the binoculars or telescope on a tripod and direct it towards the Sun (without looking through) and let the light shine on a sheet of paper placed for instance a couple of meters away. Adjust the telescope, and an image of the solar disc will show (projected) on the paper. The principle is the same as for a slide projector. The method is totally safe, but remember: Never look through the telescope when it is directed towards the Sun!.


The transit of Mercury is well visible from all over Norway. Mercury will enter the solar disc at 07:12:56 in Norwegian summertime (CET +1 hour), be in the middle of the transit at 09:52:23, and leave the disc at 12:31:46 (the times will vary with only a few minutes at different places on the Earth).

The event is visible in the whole of Europe, Africa and Asia. In Japan, Australia and New Zealand one will see the start of the transit, but the Sun will set before the transit is finished. Western parts of Africa and eastern parts of USA and South America will experience parts of the transit.

Mercury is the innermost planet in the Solar System. At a distance of almost 90 million kilometres the small planet is visible as a small spot against the large solar disc during the transit of Mercury, May 7. 2003.
Photo: NASA


The next time we will be able to see a transit of Mercury from Norway is May 9. 2016. Mercury will then be in the middle of the transit at 16:00 which starts at 12:15 and lasts until 19:45.

The next transit of Mercury visible from other places on Earth is November 8.-9. 2006. Because this is in the middle of the night, the Sun is below the horizon in Norway. November 11. 2019 there is a transit which starts at 13:37, but in the south of Norway the Sun will set during the transit.

After this, the next transits of Mercury will take place November 13. 2032, November 7. 2039 and May 7. 2049. All are visible from Norway. Because the weather is in general more stable and better in May than in November, the transits on May 7. 2003 , May 9. 2016 and May 7. 2049 is especially promising for the south of Norway.

The last transit of Mercury visible from Norway was on November 10. 1973. There was also a transit on May 9. 1970.


The times for the various types of contact between Mercury and the Sun characterises the event. 1. contact: The planet disc touches the solar disc. Right after, the planet can be seen as a nick in the solar disc. At 2. contact the whole disc of Mercury enters the solar disc. In the next hours, Mercury passes over the solar disc and at 3. contact, only touches the edge of the solar disc. At 4. contact the planet disc leaves the solar disc completely.

It is not possible to see the 1. and 4. contact in ordinary white light. A Hydrogen-Alpha filter can be used to make the planet visible against flares or the red chromosphere around the Sun.

All the transits of Mercury happens within a few days of May 8. and November 10. The trajectory of Mercury around the Sun in inclined 7 degrees with respect to the orbit of the Earth. Every year, Mercury and the Earth's planes of orbit crosses in these particular days. In addition, if Mercury is situated between the Sun and Earth in its orbit, a transit will occur. Mercury's orbit is eccentric. During the transits in November, Mercury is the closer to the Sun and will only be 10 arc seconds large (arc seconds is a measure of angles: The celestial sphere is divided into 360 degrees. Every degree is divided into 60 arc minutes, and again divided into 60 arc seconds. 10 arc seconds is therefore a 130.000 part of the whole sphere). At transits in May, Mercury is far away from the Sun (closer to Earth) and hence 20% larger. I.e. the diameter is 12 arc seconds. However, the probability of transits in May (as in 2003) are almost half the probability of transits in November. The reason is that Mercury moves more slowly when it is the farthest away from the Sun.

On May 7. Mercury will pass in front of the Sun, as seen from the Earth. With the right equipment one would be able to see it as a tiny, black spot against the intensely shining solar disc.
Illustration: Institute of Theoretical Astrophysics


Knut Jørgen Røed Ødegaard
Project leader

Institute of Theoretical Astrophysics
P.O.Box 1029 Blindern
N-0315 Oslo

Phone: +47 22 85 75 22 (Institute of Theoretical Astrophysics)
+47 992 77 172 (mobile phone)
+47 613 11 359 (private, weekend)


Created 01.01.03, modified 30.04.03 by Unni Fuskeland