Download Constellations Overview

CONSTELLATIONS
Under the blanket of
night, stars appear like a
jumble of pinpricks of
light. From the most
ancient times civilizations
have given names and
mythologies to
conspicuous patterns of
bright stars to help make
the sky seem more
familiar.
It has always been very seductive to think that
the stars are positioned in such an order that a
relationship between them might be established.
By linking
particular patters
or groups of stars
many ancient
civilizations used
them for
understanding the
universe through
the creation of
mythology.
The patterns of the constellations, then, were
invented not discovered.
They are simply distinctive, easy-to-remember
patterns of stars as seen from Earth and in
scientific terms they provide a system that
allows the easy location and identification of
individual stars.
Today, we know any relationship to be purely
superficial since their positions are only relative
to the position from which they are viewed from
Earth.
Although the constellations have no scientific
significance, astronomers have retained them as
convenient visual reference points; it is much
easier to speak of a star in Orion than to give its
geometrical position in the sky.
Although the
constellations have
changed over the years
defined boundaries were
laid down by the
International Astronomical
Union (IAU).
During the Astronomical Congress of 1928,
it was decided to recognize 88 constellations
ORIGINS
The origin of the patterns
is not known for certain
though the ancient
Chinese and Egyptians
are known to have
applied symbolic sky
maps. The basic pattern
followed today is that of
the ancient Greeks.
Some names date back to
the 7th Century BC.
Dependence on the sky
became an essential part
of many early cultures.
Some historians argue that many of the
myths associated with the constellations
were invented specifically to help farmers
construct an accurate understanding of the
sky. From ancient times farmers knew that
for most crops, you plant in the spring and
harvest in the autumn.
Therefore, by ensuring the planting took place at the
correct time the risk of a failed harvest was kept to a
minimum.
Since different constellations are visible at different
times of the year, farmers were able to use them to tell
what month it was.
As a result, accurate calendar prediction was an essential
skill and was a central aspect of astronomy up to at least
the 16th century.
It is convenient to divide the constellations into
two groups:
• Those that never set below or rise above the
horizon are called 'circumpolar'
constellations.
• The rest are divided into 'seasonal'
constellations which periodically come into
view through the year.
Which constellations are circumpolar and which are
seasonal depends on your latitude and will change
from place to place around the world.
At the Poles all constellations are circumpolar; at
the Equator all are seasonal. From the USA, most of
the Southern Constellations, a large group of 32
constellations, are always invisible and can only be
viewed by traveling south of the equator.
Circumpolar constellations are…
1.
2.
3.
4.
Seasonal
Only visible in the Southern Hemisphere
The only “official” constellations
Visible all year long
Circumpolar constellations are…
1.
2.
3.
4.
Seasonal
Only visible in the Southern Hemisphere
The only “official” constellations
Visible all year long
Circumpolar Constellations
Star Trails
It is worth noting here
that as a result of
precession the
constellations have
moved over 30º
eastwards. This means
that they no longer
correspond with the
Zodiacal signs.
The Earth rotates (white arrows) once a day about its axis of
rotation (red); this axis itself rotates slowly (white circle),
completing a rotation in approximately 26,000 years
Circumpolar Constellations
•
•
•
•
Can be seen all year long
Never fully set below the horizon
Appear to move counter clockwise
around Polaris
Caused by Earth’s Rotation
• All of the above
Examples of Circumpolar
Constellations
1.
2.
3.
4.
5.
Ursa Major – The Big Bear
Ursa Minor – The Little Bear
Cassiopeia – Queen on Her Throne
Draco- The Dragon
Cepheus- The King
• # of stars seen as circumpolar depends
on the observers latitude
• Further North the observer lives, the
more stars will appear circumpolar
• Earth turns west to east
• Sky appears to turn east to west
Ursa Major
The Great Bear
• Best known constellation
• Common name is Big Dipper
• Pointer stars- front 2 stars of the Big
Dipper point to Polaris (North Star)
Ursa Minor (the little bear)
• Ursa Minor, also called the Little Dipper, is a
circumpolar constellation.
• There are several mythological stories behind
these famous constellations. In Greek myth, Zeus
was having an affair with the lovely Callisto.
When his wife, Hera, found out she changed
Callisto into a bear. Zeus put the bear in the sky
along with the Little Bear, which is Callisto's son,
Arcas.
Ursa Major
3 Stars of Orion’s Belt
Can be used to find 2 other
constellations & a star cluster
Canis Major- (Big Dog) follow
the line made by the 3 stars
of Orion’s belt down to the
left.
–Sirius- the brightest star in the
nighttime sky is found in Canis Major
Taurus (the Bull)
• Follow the line made by Orion’s belt up
& to the right
• Aldebaran- Red star that is the eye of
the bull. It is the 13th brightest in the
nighttime sky
The most famous of all the constellations are the 12
that make up the Zodiac. All planets can be observed
only in these 12 constellations as they pass across the
sky during the course of their year. This is because the
orbits of all the planets lie within ± 8º of the ecliptic.
The Sun also moves through the Zodiac, though its
apparent motion (diurnal motion) is actually caused
by the movement of Earth.
The Ecliptic
The apparent path that the sun (and planets)
appear to move along against the star
background.
The Zodiac
Band of 12 constellations along the ecliptic.
Summary Notes
 Earth rotates on its axis, this makes most constellations appear to
rise in the east and set in the west during the night.
 Most constellations appear in many different positions in the sky
as the Earth revolves around the sun.
 There is a group of stars that appear in the sky all night long and all
year long. It seems that these stars do not rise and set, but circle the
Earth’s north pole each night. These stars are called circumpolar.
Final Thought…
Twinkle Twinkle Little Star
"Twinkling Stars" are due
to Earth's atmosphere