Celestial Sphere

Facts:It’s an imaginary sphere with earth in the center.It is useful for locating constellations and stars on a star map

Zenith: Zenith is the point on the celestial sphere directly over the head at any point of time

Nadir: Nadir is the point on the celestial sphere directly below the observer at any point of time.

Celestial Meridian:The imaginary circle passing the North and South points on the horizon and through the zenith.

Celestial equator: Imaginary line on celestial sphere in the same plane as earth’s equator.

Celestial poles: Celestial North pole and Celestial South pole are north and south points on the celestial sphere, when earth’s imaginary axis is extended all the way to touch the celestial sphere.

Celestial Coordinates: Position of a star in the mapRight ascensionEquivalent to longitude on a map. Counted in hours (not in degrees as in longitude), along the equator.DeclinationEquivalent to latitude on a map. Counted in degrees, perpendicular to the equator.

Horizon:Line where the sky meets ground or sea

Ecliptic:Path of the sun on the celestial sphere

• Constellations

– A constellation is a group of visible stars that form a pattern when viewed from Earth. The pattern they form may take the shape of an animal, or some mythological figure or some object.

– Useful to identify the position of stars in the sky

– There are 88 named constellations

Sky map – Shows location of constellations

Constellations have imaginary boundaries formed by "connecting the dots" and all the stars within those boundaries are labeled with the name of that constellation.

The individual stars in a constellation may appear to be very close to each other, but in fact they can be separated by huge distances in space and have no real connection to each other at all. For example, look at the image below of the stars which make up the constellation Orion. The stars in this easily-observed constellation are at VERY different distances from Earth!

Constellation Seasons visible(Northern hemisphere)

Main Star

Bootes Spring - Summer

Canis Major Winter - Spring

Cassiopeia All year around

Cephus All year around

Cygnus Winter – Spring – Summer

Draco All year around

Gemini Winter – Spring

Leo Winter – Spring - Summer

Constellation Seasons visible(Northern hemisphere)

Main Star

Orion Winter - Spring

Scorpius Summer

Taurus Fall - Winter

Ursa Major All year around

Ursa Minor All year around

Virgo Spring - Summer