Transcript Constellations

Constellations
Patterns in the Sky
• Stars which are “close” to each other (in angle) form
patterns called constellations.
– Not really close together
• Constellations change are unchanging year after year.
– Change over thousands of years is proper motion
Greek Myth
• Constellations are named
for characters in Greek
mythology.
• Asterisms are features
within a constellation.
– Orion’s belt
Polaris - The North Star
• Polaris is a star very near
the north celestial pole.
– About halfway up from
the north horizon in
DeKalb
– Not visible south of the
equator
• Stars in the northern
hemisphere rotate around
Polaris each night.
• Circumpolar stars don’t
cross the horizon.
Big Dipper
Polaris
• The Big Dipper is an
asterism in the
constellation of Ursa
Major.
• Two stars in the Dipper
are pointer stars to Polaris.
– End of bucket
– Handle of Little Dipper
Big Dipper
Seasonal Shifts
• The Sun masks the light of
the stars.
• Constellations appear in
certain seasons.
• Stars peak overhead two
hours earlier each month.
Ecliptic
• The earth is tilted 23º on
its axis.
• The celestial equator is not
in line with the orbit of the
sun, moon and planets.
• The sun, moon and planets
follow an imaginary curve
called the ecliptic.
Zodiac
• The constellations that lie along the ecliptic are called the
zodiac.
– 12 constellations
• The Sun passes through each one during the year.
Stars and Planets
• Stars are very numerous.
• Stars are “fixed” relative to
each other.
• Planets are few in number (5
are visible to the unaided eye).
• Planets “wander” along the
ecliptic relative to the stars.
• They produce their own light
independent of the Sun’s
location.
• Their brightness does depend
on the Sun’s location.
• They are very far away - the
Greeks understood this.
• Planets have complicated, but
predictable orbits when viewed
from the Earth.
Star Charts
• Star charts are used to
model the position of the
stars.
– Adjust for date and time
• Websites can include
planet positions, too.
www.astronomy.com