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MAGNIFICATION
To determine the magnification of a telescope and eyepiece combinantion,
divide the telescope focal length by the eyepiece focal length.
Magnification (x) = Telescope Focal Length (mm)/
Eyepiece Focal Length (mm)
Ex: 25mm Eyepiece with a 60x700 telescope
Magnification = 700mm/25mm
Magnification = 28X
FOCAL RATIO
To determine the focal ratio of a telescope, divide the focal length of
the telescope by the aperture.
Focal Ratio (f/x)= Telescope Focal Length (mm)/Aperture (mm)
Ex: Focal Ratio of a 60x700 telescope
Focal Ratio (f/x)= 700mm/60mm
Focal Ratio (f/x)= f/11.6
LIMITING MAGNITUDE
To determine the limiting magnitude of a telescope, use the aperture
in the following formula for an approximation.
Limiting Magnitude = 7.5 + 5LOG (Aperture in cm)
Ex: Limiting Magnitude of a 60x700mm telescope.
Limiting Magnitude = 7.5 + 5LOG (6cm)
Limiting Magnitude = 7.5 + (5 x 0.78)
Limiting Magnitude = 11.39
RESOLVING POWER
To determine the resolving power of a telescope under ideal conditions,
divide the aperture into 4.56.
Resolving Power = 4.56/Aperture (in inches)
Ex: Resolving Power of a 60x600mm telescope.
Aperture (in.) = 60mm/25.4 = 2.36 in.
Resolving Power = 4.56/2.36in.
Resolving Power = 1.93
ASTRONOMY FORMULAS FOR YOUR
ZHUMELL TELESCOPE
DECLINATION (DEC.)
The astronomical equivalent of latitude. Declination describes the
angle of a celestial object above or below the celestial equator. The
sky over the Northern hemisphere has a positive declination. The
sky over the Southern hemisphere has a negative declination. For
example, Polaris (the North Star) which lies nearly directly over the
North Pole, has a declination value of 90°.
RIGHT ASCENSION (R.A.)
The astronomical equivalent of longitude. Right Ascension measures
the degree of distance of a star to the east of where the ecliptic
crosses the celestial equator. R.A. is measured in hours, minutes,
and seconds as opposed to degrees. It is different than the term
“meridian”, which is used in referring to lines of longitude. Right
Ascension is referred to in “hour circles”. There are 24 hour circles of
right ascension which run from the north to the south celestial poles.
CELESTIAL EQUATOR
The celestial equator is the line of declination which lies directly
above the Earth’s equator. The celestial equator lies halfway between
the north and south celestial poles and serves as the 0° point in
measuring declination.
ECLIPTIC
The ecliptic is the apparent path of the sun through the sky over
the course of the year. Since we view the sun from different angles
throughout the year, it appears to move in relation to other stars.
The vernal (spring) and autumnal (fall) equinoxes lie at the points
where the ecliptic intersects the celestial equator. The vernal equinox
is where right ascension is at 0h (hours). The autumnal equinox can
be found at 12h R.A.
ASTRONOMY
TERMINOLOGY
ZENITH
The zenith is the point in the celestial sphere directly above your
head. The zenith varies depending upon your location. In general,
the declination point of your zenith is equal to the latitude at which
you are standing on Earth.
EPHEMERIS
The ephemeris of a planet or the sun or the moon is a table giving
the coordinates of the object at regular intervals of time. The coordinates
will be listed using declination and right ascension. Other information
such as distance and magnitude may be listed in ephemerides
(plural of ephemeris).
ALTITUDE
The altitude of a celestial object is the angular distance of that object
above the horizon.The maximum possible altitude is the altitude of
an object at the zenith, 90°. The altitude of an object on the horizon
is 0°. Altitude is measured from your point of observation and does
not directly correlate to points on the celestial sphere.
AZIMUTH
Azimuth is the angular distance around the horizon measured eastward
in degrees from the North Horizon Point. Thus, the North Horizon
Point lies at an azimuth of 0°, while the East Horizon Point lies at
90°, and the South Horizon Point at 180°. Azimuth is measured
from the point of observation and does not directly correspond to
points on the celestial sphere.
ANGULAR DISTANCE
Angular distance is the size of the angle through which a telescope
tube or binocular aiming at one object must be turned in order to
aim at another object. If you must rotate the equipment from the
zenith to the horizon, the angular distance between the two points
would be 90°.
