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Bresser 91-18001 National Geographic Manual

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The famous Ring Nebula (M57) in the Lyra constellation is often viewed as the prototype of a plan-
etary nebula. It is one of the magnificent features of the Northern Hemisphere's summer sky. Recent
studies have shown that it is probably comprised of a ring (torus) of brightly shining material that
surrounds the central star (only visible with larger telescopes), and not a gas structure in the form
of a sphere or an ellipse. If you were to look at the Ring Nebula from the side, it would look like the
Dumbbell Nebula (M 27). When viewed from Earth, we are looking directly at the pole of the nebula.
Constellation Vulpecula (Little Fox):
The Dumbbell Nebula (M 27)
Right Ascension: 19
h
59
m
(hours : minutes) / Declination: +22° 43' (Degrees : minutes)
Distance: 1,360 light years from Earth
The Dumbbell Nebula (M 27) was the first planetary nebula ever discovered. On 12 July 1764,
Charles Messier discovered this new and fascinating class of objects. We see this object almost
directly from its equatorial plane. If we could see the Dumbbell Nebula from one of its poles, we
would probably see the shape of a ring, something very similar to what we know as the Ring Nebula
(M 57). In reasonably good weather, we can see this object well, even with low magnification.
Telescope ABC’s
What do the following terms mean?
Eyepiece (3):
An eyepiece is a system made for your eye and comprised of one or more lenses. An eyepiece captures
and magnifi es the clear image that is generated in the focal point of a lens even more.
There is a simple formula for calculating the magnifi cation:
Focal width of the telescope tube / Focal width of the eyepiece = Magnifi cation
In a telescope, the magnifi cation depends on both the focal width of the telescope tube and the focal
width of the eyepiece. From this formula, we see that if you use an eyepiece with a focal width of 20 mm
and a telescope tube with a focal width of 360 mm, you will get the following magnifi cation:
360 mm / 20 mm = 18 times magnifi cation
Focal width:
Everything that magnifi es an object via an optic (lens) has a certain focal width. The focal width is the
length of the path the light travels from the surface of the lens to its focal point. The focal point is also
referred to as the focus. In focus, the image is clear. In the case of a telescope, the focal widths of the
telescope tube and the eyepieces are combined.
Lens:
The lens turns the light which falls on it around so that the light gives a clear image in the focal point after
it has traveled a certain distance (focal width).
Magnifi cation:
The magnifi cation corresponds to the difference between observation with the naked eye and obser-
vation through a magnifi cation apparatus (e.g. a telescope). Observation with the eye is considered
'single', or 1X magnifi cation. Accordingly, if a telescope has a magnifi cation of 18X, then an object
viewed through the telescope will appear 18 times larger than it would with the naked eye. See also
'Eyepiece'.
… 10 …


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