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.
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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..
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HOW TO OBSERVE THE PHENOMENON?
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!.
VISIBILITY
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.
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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 |
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NEXT TIME
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.
WHAT HAPPENS?
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.
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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
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CONTACT PERSON:
Knut Jørgen Røed Ødegaard
Project leader
Institute of Theoretical Astrophysics
P.O.Box 1029 Blindern
N-0315 Oslo
Norway
Phone: +47 22 85 75 22 (Institute of Theoretical Astrophysics)
+47 992 77 172 (mobile phone)
+47 613 11 359 (private, weekend)
Email: knutjo@astro.uio.no
