INSTRUMENTS
ASTRAL TELESCOPE
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First of all it is necessary to say that astronomy requires
certain very specific atmospheric conditions and these requirements change according to
the object being observed: Sun, Moon and planets are less demanding subjects to observe
from the point of view of the quality of the sky and so the observation of these may gives
the observer considerable satisfaction even in a brightly-lite city or when the sky seems
muddy or dirty. Stars, stellar masses, nebulae and galaxies on the other hand are
"susceptible'' and are best observed when the sky is clean, when there is no moon, no
artificial light and very little humidity. ALL observation should be carried out in the
open and not through glass. As we have already said, it is advisable to leave the
telescope out in the open for half an hour before starring observation in order to allow
the instrument rime to accustom itself to the prevailing conditions.
Bear in mind that a telescope of fairly large diameter will allow you to observe more, and
in greater detail and will permit a greater degree of magnification than will a telescope
of lesser diameter. It will also permit observation of weaker objects.
It is advisable to prepare ail that you will need ahead of rime and to plan a rational
observation schedule. Identify what you want to observe in a good Astronomy Atlas or Star
Map or consult an Astronomy Almanac where you will be able to see the positions of what
you want to observe on any particular day of the year.
The Astronomy Atlas is useful to have with you even when you have set your telescope up
for observation so that it is to hand for consultation. A small torch with a red filter
(so as not to disturb eyes that have adjusted to the dark), an accurate watch or timepiece
and a notebook and pencil so that you can take notes. The telescope should be mounted in a
stable position with what you need ready to hand.
HOW
TO AIM THE TELESCOPE AT CELESTIAL OBJECTS
After regulating the telescope as previously described, you will be
able to aim the telescope at the objects you wish to observe in one of the following ways:
The first of these methods is, without doubt, the most popular with astrophiles, both for
its ease of use and its speed. It requires, however, a certain familiarity in the handling
of the instrument which has to be mounted and regulated correctly, above all as regards
the correct alignment of the finder with respect to the main telescope.
Aiming at a celestial object with the naked eye is very simple. With freedom of movement
and the tube of the telescope in your hand, look through the finder and move the tube in
the direction of the desired object. Once the object is within the frame of the finder,
block the movement of the instrument. Using micrometric movements, bring the object to the
center point of the frame. If the finder bas been correctly aligned, the object will be
centered in the ocular of the main instrument also. In order to facilitate this type of
focusing, the use of an ocular with low level magnification is useful. With this method it
will be easy to aim at most of the planers in our solar system, thousands of stars and the
brightest of the stellar masses, nebulae and galaxies.
In order to aim the instrument at objects invisible to the naked eye, a map of the sky or
a star atlas would be necessary. Once you have identified the object you wish to observe,
make a note of its position with respect to the brightest stars in the constellations
nearest to it. Get one of these stars within the finder of your instrument, and, with the
ocular to your eye, move the telescope to the point where, according to your map, the
object you wish to observe should be. It is necessary to bear in mind that the finder
shows the image in reverse, whereas the stellar map shows the sky correctly.
The second method requires a precise alignment of the equatorial mounting of the
instrument with the Celestial North Pole. The method described in the appropriate
paragraph in not sufficiently precise to allow accuracy in this method but let us imagine
that it is.
The movement of the telescope will be effected moving along the axis of the Right
Ascension and Declination. For no reason whatsoever should it be necessary to move along
the inclination and horizontal rotation of the Polar axis.
Such movements should be considered as reserved for the polar alignment of the mounting
process. Once the aiming process has been carried out by unblocking the movement on the
axes, so that the object has been placed at the center of the finder, the levers should be
blocked once again. Micrometric movements by means of the flexible knobs regulating these,
if possible with the instrument in ques- tion, facilitate the whole process.
Look for the Declination value of the stars in a star atlas. For example the bright star
Vega can be found at +38 ° 44' of Declination. Unblock the Declination screws, rotate the
telescope in declination until you can read the value of 38 ° and then tighten the screws
once more. This will allow the telescope to turn around the celestial pole at a fixed
distance of 52 ° (90 ° - 38°).
The map or star atlas will be able to help you to identify the position of the stars. The
sky has been divided like a huge clock divided into twenty-four hours. You will see that
the Great Bear (Ursa Major) is to be found in a position between the Right Ascension of 11
and 13 hours and 45 minutes. Because Vega is situated at 18 hours and 35 minutes it will
be possible to aim the telescope. By turning it 1/4 rimes to the right of the polar axis
with respect to the two stars of the Pole (found at the Right Ascension position of 11
hours) you will find yourself in the vicinity of the bright star Vega in the constellation
Lyra.
Once you have identified the position of the stars making up the Great Bear, unscrew the
screws that block the Right Ascension.
Rotate the telescope to align the tube with respect to the two main stars of the pole. Now
the telescope is aimed at that part of the sky corresponding to the Right Ascension = 11
hours.
Tighten the screws.
Turn the finder in your hand until you read 11 hours. In this way you will have
"hooked" your telescope to the system of celestial coordinates for the date and
the time in which you are observing. Rotate the flexible knobs governing the Right
Ascension axis by moving the telescope about 1/4 towards the right until you read on the
finder the value of 18 hours and 30 minutes. Look in the finder. The bright star near the
center of your frame is Vega.
Using the flexible cable of Right Ascension and Declination, regulate the position of the
telescope, while looking through the finder until the star is perfectly centered within
your frame. Now look through the main telescope and focus.
The subdivision of the celestial sphere into twenty-four hours is derived from the rime
earth takes to rotate, determining the division of the day into twenty-four hours. Every
star has its own position in the celestial sphere and this can be identified from a pair
of coordinates: The Right Ascension (which as we have already said is indicated in hours,
minutes and seconds) and the Declination (indicated in degrees, minutes and seconds, with
values going from 0 to +/- 90°).
The zero value of the Right Ascension corresponds to the first point of
Aries, a point chosen arbitrarily which is to be found between the zodiacal constellations
of Aries and Pisces, whereas the zero value on that of Declination corresponds to the
Celestial Equator, the projection into the sky of the earth's equator (fig. 9).
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