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CONSTELLATIONS
• Constellation: formation of stars
perceived as a figure or design.
– 88 recognized groups named after characters
from classical mythology and various common
animals and objects.
• Asterism: star patterns that are not
constellations. They may be contained
within single constellations or between
multiple constellations.
• Ecliptic: the great circle representing the
apparent annual path of the sun; the plane
of the Earth's orbit around the sun; makes
an angle of about 23 degrees with the
equator; "all of the planets rotate the sun
in approximately the same ecliptic"
• Declination: one of the two coordinates of
the equatorial coordinate system.
Comparable to Latitude. Expressed as an
angle with respect to the celestial equator.
• Right Ascension: a celestial longitude
measured in the direction of the Earth’s
rotation. The notation adopted for right
ascension is in terms of hours and minutes
with 24 hours representing the full circle.
• Circumpolar star: a star that as viewed
from a given latitude on Earth, never
disappears below the horizon, due to its
proximity to one of the celestial poles.
Visible for the entire night (and throughout
the day if it wasn’t for the sun’s glare)
every night of the year.
The North Polar Sky
declination 90° to 50°
• Polaris lies less than 1° from the north
celestial pole
• For observers in the Northern
Hemisphere the stars are circumpolar
• The viewer’s latitude will determine
how much of the sky is circumpolar
The South Pole Sky
-50° to -90°
• There is no southern equivalent of
Polaris
• Many of these stars are circumpolar for
observers in the Southern Hemisphere.
Equatorial Sky
(Chart 1: 21h to 3h contains 0h line of right ascension)
• Observed during evenings in Sept, Oct
and Nov
• Contains the Vernal equinox in Pisces
(the Sun will pass through here in late
March)
Equatorial Sky
(Chart 2: 15h to 21h)
• Observed during evenings in June, July
and August
• Contains the point where the sun
reaches its most southerly declination
in Sagittarius around Dec 21
Equatorial Sky
(Chart 3: 9h to 15h)
• Observed on evenings in March, April
and May.
• Contains the Autumn equinox in Virgo
around Sept 21
Equatorial Sky
(Chart 4: 3h to 9h)
• Observed during evenings in
December, January and February
• Contains the point at which the Sun is
furthest north on the border of Taurus
and Gemini around June 21