Zon Mosaic Pro5 User's Guide Page 96

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96 Starry Night User’s Guide
Solar System Object Information Fields:
For objects within our solar system, the
following information fields are present:
Radius: The object’s radius (if known).
Apparent magnitude: The object’s
apparent magnitude, a measure of its
brightness in the sky. See “Magnitude
” on
page 94 for more information on apparent
magnitude.
Age: Only an option for the Moon, this
gives the Moon’s current phase, and the
number of days that have passed since the
Moon was last new.
Orbit Size: The radius of the orbit that the
object makes around its parent body.
Angular Size: This measures the angular
width of the object (the field of view that it
occupies in the sky).
Disc Illumination: This shows how much
of a planet’s face is illuminated by sunlight
(the rest is in shadow), as seen from your
current position. For example, when the
Moon is half full, its disc illumination is
about 50%.
Planet oblateness: This measures how
much an object is “squished”, in other
words, how much it deviates from a
perfect sphere. A perfect sphere would
have an oblateness of 0. The larger an
object’s oblateness, the more “squished” it
is.
Mass: The object’s mass (if known).
Max. Mag. From Earth: The apparent
brightness of planets and other objects in
the solar system changes as the object
moves in its orbit, due to the object’s
changing distance from Earth and the
object’s disc illumination. This field gives
the apparent magnitude of the object when
it is at its brightest.
Length of Sidereal/Solar Day: An object’s
sidereal day is the time that it takes to
rotate once, relative to the fixed stars. An
object’s
solar day is the time that it takes to
rotate once, relative to the Sun. This is also
the average time between sunrises on the
planet’s surface. These two time periods
differ by a large amount only when the
length of a planet’s sidereal day is a
significant fraction of the length of the
planet’s year. On Earth, the time periods
are almost identical, with the 24 hour solar
day being only four mintes longer than the
sidereal day.
Length of Year: For objects that orbit the
Sun, a year is the amount of time that it
takes for the object to complete one full
orbit.
Other Object Information Fields:
The information fields for objects other
than stars and solar system objects will
vary. Often the only pieces of information
are the object’s magnitude and angular
size.
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