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| The Celestial Sphere |
Celestial Sphere It
is very large imaginary sphere surroundings the
Earth and to which the Sun, the Moon, the Planets,
and the Stars are considered
to be attached
HOW DOES ASTRONOMERS KEEP TRACK OF THE SKY
WHEN THE EARTH IS CONSTANTLY MOVING?
In
order to locate an object in
the sky, it is necessary to
set
up a reference system of
coordinates.
SYSTEM
OF COORDINATES
1. TERRESTRIAL COORDINATE SYSTEM
Latitude and Longitude
2. CELESTIAL COORDINATE SYSTEM
This coordinate system is an extension of
the terrestrial system on
to the celestial sphere.
3. THE ECLIPTIC SYSTEM
Based on the Earth's orbit around the
Sun.
4. THE HORIZON SYSTEM
A completely local system that is based
on an observers latitude
and longitude and the time.
TERRESTRIAL COORDINATE SYSTEM
Latitude = north/south measurement (degrees).
Latitude is based on a scale of 90o at poles and 0o at the equator.
Longitude = east/west measurement (degrees).
Longitude is based on 0o at Greenwich and 180o at International Date Line.
THE ECLIPTIC SYSTEM
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Cardinal Points on the Ecliptic
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•Based on the Earth's orbit around the
Sun.
•Ecliptic is the plane of the Earth's
orbit projected on to the celestial sphere.
–The 12 zodiac constellations are located
in a band following
the ecliptic.
–The Sun, Moon, and planets are found on or near the ecliptic.
–The ecliptic is tilted 23.5o
with respect to the celestial
equator.
CELESTIAL COORDINATE SYSTEM
•This coordinate system is an extension of the terrestrial system on to
the celestial sphere.
–Declination = north/south measurement
•Units of degrees.
•Based on 90o at poles and 0o at the equator.
–Right Ascension = east/west measurement
•Units of time.
•Based on 0h at March Equinox point in the
sky.
•Measured continuously from 0h to 24h.
THE HORIZON SYSTEM
The horizon system is a completely local
system that is based on an observer’s latitude and longitude and the time.
–Altitude =
vertical measurement.
•Altitude is based on, 0o
at horizon and 90o at the zenith.
–Zenith is
the point in the sky directly over the observer.
–Azimuth =
direction measurement.
•Azimuth is based on:
north
= 0o,
east = 90o,
south = 180o,
west = 270o.
–The meridian
is
a vertical circle that runs due N/S.
•When celestial objects transit the
meridian, they are highest in the sky.
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| Horizon System |
