AstronomyStudy of stars, galaxies and our

own insignificance

Why study astronomy?

• Learn about our origins/history of universe• Our place in the “cosmos”• Explanation & appreciation for motions

and phenomena:– Day/night, seasons, eclipses, tides, auroras,

sunspots, shooting stars, sun/stars/planets/moon motions

• Calendar• Future?

So you think you’re special?Comparison with Sun

• Size

• age

• composition

• Unique?

The “Big Bang”

• “to make an apple pie from scratch you must first invent the universe” –Carl Sagan

• 13.7 billion years ago all matter and energy expanded from a single hot, dense point in time “singularity”

• Temperature fluctuations in oldest light in universe

• Slight clumping of material in young universe, Clumps became galaxies

• First stars (200 million years after Big Bang) gas condensed to fusion temps.

• More stars• Now: billions and billions of

stars and galaxies

The night sky

• Window to the universe

• During day, “sun” star is so much brighter we can’t see the rest of the universe

• Moon, planets, stars, galaxies, star clusters, galaxy clusters, nebula

• Study the light that reaches us

• Basic observation techniques

Observation

Stars & constellations

• Nearest star?

• Nearest star other than sun= Proxima centauri (4.3 light years)

• Brightness: how big, how hot, how far

• Color: red=cool, blue=hot

• Star patterns=constellations

88 constellations

• In Wellesley: Orion, Taurus, Cassiopia, Pleiades, big dipper, Gemini

• Why don’t we see Orion & Taurus now?

• Circumpolar constellations=dippers, Cassiopia

• How do you find….

Motions of the sky

• All planets orbit the sun, sun rotates• Universe is expanding which means most stars

are moving farther apart• Most dramatic motions caused by EARTH

motions: – Rotation,revolution

• Rotation causes: rising/setting• Revolution causes: seasons/path of sun,

difference in stars viewable during the night

Earth/moon system

• Motion is counter clockwise (eastward) takes ~4 weeks

• Relative positions of earth/moon/sun cause phases and eclipses

• Why don’t we have eclipses every time we have a full moon?

Orbit inclined

It’s all in your perspective!