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Mapping the Celestial sphere Some definitionsLocating stars and deep space
objects Describing an objects position
The Celestial Sphere
Some Definitions
• Celestial (Heavens)– Imaginary Points in space directly in line with
the earth• Celestial sphere:
– The canopy of stars resembling a painting in the night Sky
• Celestial Poles:– Points where the earth’s axis intersects with
the celestial sphere
Celestial North Pole
• Polaris (North Star)
Celestial South Pole
• No Southern star
• Southern pole: Use the southern cross:
Some Definitions
• Celestial Equator– Extend the
earth's equator outward to the celestial sphere
• Describing an objects position in the night sky with respect to the celestial Equator
1. Declination • (Latitude)
2. Right Ascension • (Longitude)
Location of a star• Betelgeuse (470 light-years away; 20x > Sun)• RA: 5h 55m 10.2s east of vernal equinox• dec: 7°24’26” north of celestial equator
Some Definitions• Zenith
– Imaginary point on celestial sphere directly overhead (90°)
• Nadir– Exact opposite of the
Zenith (you can not see it)
• Horizons– Place where the earth
and sky appear to meet – Halfway between zenith
and nadir
Some Definitions• Meridian
– Imaginary north-south line on the celestial sphere that is directly overhead on the observer
Morning half (a.m.) Evening half (p.m.)
It cuts the celestial sphere into two halves
Constellations • Every star and object in the
celestial sphere is in a constellation
• To locate a star– Specify a constellation– Rank it by order of brightness
•Brightest star?Sirius
Found in Canis Major Also known as alpha Canis Major (or CMa)
Putting the maps together
Not a constellation
• Asterisms– A small grouping of stars, that do not make a
constellation – E.g.. The big dipper is part of Ursa Major
Location of nearest stars• Alpha Centauri,
Beta Centauri, and Proxima Centauri
• RA: 14h 29m 41s east of vernal equinox
• dec: -62°40’46” south
• Proxima Centauri (4.2 l-y but too dim to see w/o telescope)
• Alpha and Beta (4.4 l-y; apparent magnitude of -.28 combined)
Changing Constellations
• Throughout the seasons positions of constellation change do to earths revolution around the sun
• Over long periods of time constellations can change– Star positions mover relative to each other on
the celestial sphere