constellations a natural human tendency is to see patterns and relationships between objects even...

ConstellationsA natural human tendency is to see patterns and relationships

between objects even when no true connection exists.

Long ago, people connected the brightest stars into configurations called constellations, which ancient astronomers named after mythological beings, heroes, and animals—whatever was important to them.

Does that cloud look like a “bunny” to you.

OR

What do you see in that ink blot?

Orion• Some locations are better

• Stars are widely varied in color

Orion

Ursa Major

Ursa Major

Ursa Minor

Ursa Minor

Scorpius

Scorpius

Cygnus

Cygnus

Sagittarius

Sagittarius

Cross CulturesAstronomers of ancient China saw mythical figures different

from those seen by the ancient Greeks, the Babylonians, and the people of other cultures, even though they were all looking at the same stars in the night sky.

Interestingly, though, different cultures often made the same basic groupings of stars, despite widely varying interpretations of what they saw.

For example, the group of seven stars usually known in North America as "the Dipper" is known as "the Wagon" or "the Plough" in Western Europe. The ancient Greeks regarded these same stars as the haunches and tail of "the Great Bear," while the Egyptians saw them as the leg of an ox.

NavigationReasons to Group stars and create constellations:

• Entertainment

• Honor – Hero Hall of Fame– gods or leaders

• Keep track of where things are and the time– Calendars, Events

• Navigation

Patterns are Deceiving

Constellations are NOT

physically associated

with each other, they just happen

to be along your line of sight.

Our Moving Observatory

Star trails

Looking SouthEast

Looking North

What’s Your SignThe Sun’s Position Determines your sign.

The Zodiac

Summer ConstellationsLooking South

Lyra and CygnusDirectly

Overhead

After Sunset

in the summer

and early

fall.

Winter ConstellationsLooking South

Star Atlas ArtistryCan You Find:

Orion

Taurus

Canis Major

Cancer

Gemini

HipparchusMost atlases of today have their origins with those

that were derived from Hipparchus and used his

“magnitude” system.

1st Rank Stars (The brightest stars in the sky)

6th Rank Stars (Barely visible with the unaided eye)

Later, the magnitudes were rigorously defined so

that a 5 magnitude difference = 100 x the intensity.

MagnitudesMagnitudes

are more

precise

and changes

in intensity

are matched

with apparent

magnitudes.

Vega = 0.0

Magnitude ScaleNote:

M = 5 - 0 = 5

I = 100 1 = 100

or

M = 8 - 3 = 5

I = 1600 160 = 100

Brightness ScaleI1/I2 = 2.512(m2-m1)

I = intensity mv = apparent magnitude

• Horizon based coordinate system– Horizon dependent (different for each observer)

Altitude - Azimuth

S

W

N

E

• Horizon based coordinate system– Horizon dependent (different for each observer)

• Azimuth Angle (degrees)– measured CW from N to E– N = 0o, E = 90o, S = 180o, W = 270o

Altitude - Azimuth

S

W

N

E

N

0

180

90 E

S

270W

• Horizon based coordinate system– Horizon dependent (different for each observer)

• Azimuth Angle (degrees)– measured CW from N to E– N = 0o, E = 90o, S = 180o, W = 270o

• Altitude Angle(degrees)– horizon to star– Horizon = 0o

– Zenith = 90o

Altitude - Azimuth

S

W

N

E

N

0

180

90 E

S

270W

“Bowl” DiagramOrienting yourself to a local horizon.

N S

W

NCP

Zenith

Celestial Equator

Celestial Orientation

Right Ascension - Declination• Geocentric Coordinates

– Observer Independent

Towardthe VernalEquinoxe (Position of the Sun on March 21-22

Celestial Equator(Earth’s Equator)

North Celestial Pole (NCP)

Right Ascension - Declination

Towardthe VernalEquinoxe = 0 hours

Celestial Equator(Earth’s Equator)

• Right Ascension (hours)– Measured from the Vernal Equinoxe along the C.E.– Vernal Eq. = 0 hours

RA

Right Ascension - Declination

Towardthe VernalEquinoxe = 0 hours

Celestial Equator(Earth’s Equator)

• Declination (degrees)– Measured from the Celestial Equator to the Pole– CE = 0o

– NCP = 90o

NCP

DEC

Sky Atlas

Right Ascension

Dec

lina

tion

Magnitude

Sky Atlas

Constellation

Lyra,

Bright Star

Vega