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with highly reflective paper or a grid
template, if necessary (see notes below).
Lay the projection surface with the flaps
downward into the bottom of the housing,
so that it touches the front wall and the
two flaps fit snugly into the corner of the
housing curvature.
Step 28: Remove the protective foil from
the plane mirror. It might be necessary to
slightly lift a corner with a knife.
Now the Solar Projector is complete.
Chapter D
The Base
In order to adjust the altitude of the Solar
Projector between the horizon and the
zenith, the base has a curved surface
which holds the rounded back of the
housing. This simple but efficient way of
fitting the projector is known as a
Dobsonian mount, after its inventor, and is
often used for astronomical telescopes.
Step 29: Fold the flaps of the trapezium
shaped left outer side [D1] backwards and
the many small flaps of the left inner side
[D2] forwards. The top edge of the outer
How to use your Solar Projector:
1. Place the objective in the objective guide and put the cassette in the slipcase.
2. Place the Solar Projector in the Dobsonian base and put it up to the Sun so that the little bright point from the objective hits the
convex mirror, somewhat above its centre.
3. Put the objective in focus by pushing it forwards or backwards so that a clear image of the Sun appears on the projection surface.
4. The Sun moves, so the image of the Sun will also move. Rotate and tip the projector so that the image is once again easy to see.
The focussing of the objective will only need to be changed when you swap the convex mirrors.
5. Important: Do not leave the Solar Projector unmonitored with the objective in the direction of the Sun. The focussed light from the
Sun could move away from the mirror and burn a hole into the cardboard.
Frequently asked questions:
1. Why doesnʼt the Solar Projector need a solar filter? Looking directly at the Sun, whether with or without a telescope should
always be done with a solar filter. But with the Solar Projector you are not looking at the Sun, but at a projected image. This image
is no more dangerous than a piece of paper with the Sun shining on it.
2. What can I observe with the Solar Projector? Most importantly sun spots, but also solar eclipses and planet transits. Under
good conditions it is even possible to observe the landscape.
3. Are there always sun spots visible? The number of sun spots changes during a cycle of approximately 11 years. The last
minimum was in 2009, the next maximum is expected in 2013. When near a minimum, sun spots are only visible with a very
powerful telescope (with solar filter). You can find more information about sun spots on the internet at www.wikipedia.org.
4. Can sun spots change in size and position? Yes, sun spots (which often consist of groups of smaller spots), grow and shrink,
and move over days from left to right over the solar surface. The reason for this is the rotation of the solar sphere around its own
axis (the rotation period is 25 days on the solar equator, 35-40 days at the poles). If you follow the position of a regular round spot
near the centre of the solar disk over a few days it will get ever thinner because of perspective distortion.
5. How often can I see solar eclipses?
Approximately twice a year somewhere on Earth, but usually only in very specific, and often very inaccessible places. Lists of
solar eclipses can be found on Wikipedia as well.
6. What is a planetary transit?
The orbits of Mercury and Venus around the Sun are within the orbit of the Earth. Therefore occasionally Mercury or Venus are
exactly between the Earth the Sun, so that for a short time they move past the solar disk. Such a planetary transit is a rare
occasion, because the orbits of the planets donʼt lie in the exact same plane.
side is exactly as long as the straight
edge of the inner side. Glue the inner side
and the outer side back to back (with the
printed sides outwards) so that these two
equal edges are flush.
Step 30: Do the same with the right outer
side [D3] and right inner side [D4].
Step 31: Fold the two flaps of the curved
surface [D5] backwards and gently curve
the surface by holding one of the flaps
and dragging the part over a straight table
edge or similar, with the printed side
facing downwards: the printed side should
be the inside of the curvature. It should be
curved enough to fit approximately the
line of the flaps of the inner sides [D2] and
[D4].
Step 32: Take one of the two outer sides,
with the glued-on inner side and apply
glue to the printed side of the small flaps.
Lay the outer side face-down on your
work surface, stand the curved surface
[D5] on the inner side and stick the flaps
to the back of the curved surface. Take
care that the ends of the curved surface
do not stick out beyond the ends of the
inner side. Stick the other inner side on
the other edge of the curved surface in
the same way.
Step 33: Fold all the flaps of the base
plate [D6] backwards and place it, printed
side downwards, on your work surface.
Stick first one, and then the other flap to
the back of the two side pieces that are
joined by the curved surface. It is best to
do this as follows: Put glue on one of the
two flaps and place the curved surface
with the side pieces onto the base plate,
so that the side pieces line up with the two
flaps. To glue it in place it you can push
against the pieces on the outside with
your hand and on the inside with a pencil
or similar. Glue the second flap in the
same way.
Step 34: Finally, you need to glue the
front side [D7] and the rear side [D8] of
the base onto the flaps of the two
remaining openings. Lay the base on a
flat surface for this and ensure that the
base plate stays square against all the
edges while glueing.
Congratulations! Now youʼve put it
all together and you are ready for
your "First Light", as astronomers
call the time of the first observation
with a new piece of equipment. We
wish you many interesting hours
with your self-built Solar Projector!
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