SMALLEST LARGEST

UNIVERSE

TIME

SPACE

EVERYTHING

SOLAR SYSTEM STARS GALAXIES

MILKY WAY

PLANETS

OTHER CRAP

SUN

NORTH STAR

Thought Question:

If you could see stars during the day, this is what the sky would look like at noon on a given day. The Sun is near the stars of the constellation Gemini. Near which constellation would you expect the Sun to be located at sunset?

A. LeoB. CancerC. GeminiD. TaurusE. Pisces

Thought Question

Which of the following describes when constellations are visible from San Diego (if it is dark enough and the clouds cooperate)?

A. You could observe any constellation tonight at midnight.

B. You could observe any constellation sometime during the night.

C. You could observe any constellation on some night during the next year.

D. Some constellations will never be visible from here.

NORTH STAR

CONSTELLATIONS: for orienting ourselves in the sky:

Being a Good Astronomer

Complications in finding things:

• Earth is a sphere (people in different places see different stars)

• Earth rotates (stars continually move across sky)

• Earth orbits the Sun (stars don’t appear in same place from month to month)

• Some of our targets are moving too…

ATMOSPHERE

Being a Good Astronomer

High in the sky is best because…

the more atmosphere you have to look through:• the more light is blocked• the more the colors are affected

ATMOSPHEREHIGH ALTITUDELOW

ALTITUDE

Where in the Sky?To describe position in sky,

need two coordinates:• Altitude (ALT): angle

above horizon

0º: horizon

90º: zenith

• Direction (DIR): angle clockwise from N measured around horizon

0º: N 180º: S

90º: E 270º: W

NORTH STAR

SN

E

W

N

E

W

S

NORTH STAR

ZENITH

Being a Good Astronomer

Best telescopes usually scheduled months in advance:• must be able to predict when an object will be up• light from Sun, Moon should not interfere

ATMOSPHERE

Stars Move?

Thought QuestionIn the past, several TV shows (NBC Nightly News, The Daily

Show) had opening graphics which showed the Earth spinning the wrong way. If you were watching Earth from a stationary position out in space (as shown below), what direction does it spin?

A. Left to right

B. Right to left

Celestial Sphere

Stars appear to move as if attached to a sphere rotating around Earth

• Celestial poles: above Earth’s N and S poles

• Celestial equator: directly above Earth’s equator

Earth Surface Coordinates

SOUTH POLE90º S

NORTH POLE90º N

EQUATOR0º

Celestial Coordinates

SOUTH CELESTIAL POLE

NORTH CELESTIAL POLE

CELESTIAL EQUATOR

DECLINATION LINES

SOUTH CELESTIAL POLE

NORTH CELESTIAL POLERIGHT

ASCENSION LINES

Celestial Coordinates

declination (DEC): like latitude on Earthnorth celestial pole: +90ºcelestial equator: 0ºsouth celestial pole: -90º

right ascension (RA): like longitude on Earth

BUT… counted in hrs, increases toward east

north celestial pole

The Sky from San DiegoMost stars rise in east half of sky,

and set in west half:

NORTH CELESTIAL POLE

LOOKING SOUTH

N

W

S

E

HORIZON

circumpolar: stars that don’t rise or set for a person

LOOKING NORTH

stars circle in 23h56m

Thought QuestionIf you watched the star pictured below from San Diego over

several hours, what would happen?A. Its altitude and direction wouldn’t change.B. Its altitude would change, but direction wouldn’t.C. Its direction would change, but altitude wouldn’t.D. Both its direction and altitude would change.

HORIZON

N

E

W

S

Using a Telescope

A telescope pointing at one ALT and DIR doesn’t move

BUT a star’s ALT and DIR both change during night

• Is there a better way?