Polar alignment
1.What the polar alignment is
Polar finder reticle for both the Northern and
Southern Hemispheres
Stars rise from the east and set in the west
every day. This is due to a phenomenon called
“diurnal motion,” which results from the rotation
of the earth. The center of this motion is located
around the North Star, as viewed from the
earth. Therefore, stars appear to rotate around
the North Star. The equatorial telescope can
track this diurnal motion with ease because it
has a polar axis that simulates the same motion
as the rotational axis of the earth. For proper
tracking, however, the polar axis must be set so
that it's parallel with the rotational axis.
2.Placing the reticle illuminator
Screw the reticle illuminator into the polar scope
and insert the plug into the reticle illuminator
power socket on the Skymemo RS. The
brightness of illumination can be adjusted
through the reticle illuminator intensity control
using a precision screwdriver. Next, turn the
polar finder (focus adjustment) part of the polar
scope until the reticle pattern is clearly visible.
Strictly speaking, the earth is a rotating ellipsoid
that bulges slightly in the direction of the
equator. As the gravitational pull of the sun,
moon, etc., acts upon the mass of this bulged
part of the earth, the earth moves like a pivoting
top by changing its direction periodically. As a
result, we the star watchers see the north and
south poles of the skies move along a large arc
of 23.4° in radius around the pole of the ecliptic
(precessional circle) in periods of approximately
25,800 years. This translates into 50.27” per
year. From the viewpoint of observation of star
positions--essentially nutation, polar motion,
aberration of light, annual inequality,
atmospheric refraction, etc.--should also be
considered. However, because these deviations
are minor, correcting a general change of
precession is considered enough for the
amateur sky watcher. The Skymemo lets you
make this correction simply by shifting the
positions of reference stars.
the Big
Dipper
the
Southern
Cross
Actual starry sky
The Northern Hemisphere
The Southern Hemisphere
Cassiopeia
Achernar
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