Celestron StarSeeker 80mm Instrukcja obsługi - Strona 8
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The celestial parallels of latitude are called "coordinates of declination (Dec.)", and like the Earth's latitudes
they are named for their angular distances from the equator. These distances are measured in degrees,
minutes and seconds of arc. There are 60 minutes of arc in each degree, and 60 seconds of arc in each arc
minute. Declinations north of the celestial equator are "+" and declinations south are "-". The north pole is
+90 and the south pole is -90 .
Figure 4
line in the sky. So, R.A. coordinates are marked off in units of time eastward from an arbitrary point on the
celestial equator in the constellation Pisces. The prime R.A. coordinate which passes through this point is
designated "O hours O minutes O seconds". We call this reference point the vernal equinox where it
crosses the celestial equator. All other coordinates are names for the number of hours, minutes and seconds
that they lag behind this coordinate after it passes overhead moving westward.
Given the celestial coordinate system, it now becomes possible to find celestial objects by translating their
celestial coordinates using telescope pointing positions. For this you use setting circles for R.A. and Dec. to
find celestial coordinates for stellar objects which are given in star charts and reference books.
B.
Polar Alignment
To make tracking the stars easier, rough polar alignment is required.
1.
The right ascension (polar) axis should be pointed towards the North Pole (see the illustration below).
2.
The equatorial mount should be level.
3.
Your latitude should be set (see section 3.A).
The celestial meridians of longitude are called
"coordinates of right ascension (R.A.)", and like
the Earth's longitude meridians they extend from
pole to pole. There are 24 major R.A.
coordinates, evenly spaced around the 360º
equator, one every 15º.
longitudes, R.A. coordinates are a measure of
time as well as angular distance. We speak of the
Earth's major longitude meridians as being
separated by one hour of time because the Earth
rotates once every 24 hours (one hour = 15°).
The same principle applies to celestial longitudes
since the celestial sphere appears to rotate once
every 24 hours. Right ascension hours are also
divided into minutes of arc and seconds of arc,
with each hour having 60 minutes of arc and each
arc minute being divided into 60 arc seconds.
Astronomers prefer the time designation for R.A.
coordinates even though the coordinates denote
locations on the celestial sphere, because this
makes it easier to tell how long it will be before a
particular star will cross a particular north-south
Like the Earth's
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