On Thursday 9th of November 2006, Mercury passed between the earth and
the sun. The transit was completed in about 5 hours and was
easily seen from the east coast of Australia. Although Mercury will
transit the sun 14 times in this century, it will only be able to be
seen from some locations for each event. The next transit that can be
seen from Canberra is in 2032, the two before this date will not be
able to be seen.
The best way to watch a transit of either Mercury or Venus, to watch sun spots, is to use
the so called projection method. This involves pointing your telescope
at the sun and pointing the eye piece at a flat white surface. Avoid
looking at the sun and DON'T look through the eye piece at the sun as
this is a quick way to become blind. You will find that even holding a
hand near the eye piece when the telescope is pointing at the sun will
be very hot.
I have a reflector. To point the telescope at
the sun, I looked from the mirror cell along the telescope towards the
open end. I positioned it so that I couldn't see the sun. I then held
my hand in front of the eye piece and moved the telescope a small
distance in different directions until I could see the bright white
spot of light from the sun. I locked the mount. I could then track the
sun with the fine controls. It generally takes two or three goes at
this process before you get it set up.
For my white surfact I taped a sheet of A3 paper to a music stand. If I
was doing this again I would find something that was stiff in itself -
say some white shiny card - of about the same size. Doing photography
is also difficult because the sun shines at right angles across your
projection surface. For photography I would consider some form af
screen along the edge of your projection surface toward the sun. This
will put the surface in shadow and improve the projection.
None of the material I have read about this method talks about which
eye piece to use. The easy answer is to use the lowest
magnification. I have a 25mm plossl that gives me 36x and a 10mm plossl
that gives me 90x on my 900mm FL telescope. I intended to use the 25mm
however I accidentally loaded the 10mm. On my first attempt I failed to
focus to the point where I could see Mercury. After fiddling
for a while I discovered the mistake. Once I had changed to the 25mm I
managed to focus to see Mercury. I found that as the magnification went
up focusing became harder and it was easy to go the full range of focus
adjustment without seeing Mercury. Higher magnifications are actually
counter productive since you want as much light and contrast as
possible and you can get larger sizes just by moving your projection
surface further from the eye piece.
The following three pictures were taken around 7:00am about an hour
into the transit. You can see a large irregular dot towards the left
that is a sun spot. The smaller round spot towards the right
is the silhouette of Mercury. One challenge was that the telescope was
in the way when taking photos:-{)=.
