Why Astronomy?

For countless centuries, humans have wondered about objects they saw in the sky and worried about

how they affected their lives.

Astronomy ≠ Astrology

Daily Motion of the Sun

• Even the most casual observer is aware that the sun makes a daily journey across the daytime sky.

• It always rises in the eastern sky and sets in the west.

Yearly Motion of the Sun

• Then they would discover that it isn’t so simple. The sun’s path is higher in summer than in winter.

• This cycle repeats itself every 365 days.

The Sun’s Height Changes with Your Position…

• Travelers to other parts of the world discovered that the Sun is higher in the tropics and lower in colder regions.

• How could this be? What does that suggest about the shape of the Earth?

Keeping Track of the Sun…

The Moon: The Heavenly Object That Changes Shape

This cycle of phases takes around 30 days - a month!

Tracking Both the Sun and the Moon:

• Monuments that are aligned to important positions of the sun and moon are found around the world.

• The most famous is Stonehenge, which could have been used to mark the seasons and even eclipses of the sun and moon.

ECLIPSES!

• As cultures developed, it was important to be able to predict rare events, like eclipses.

• By plotting solar and lunar positions over many years, they could find times when such scary events might occur.

The Nighttime Sky• After the moon, the next

most obvious characteristic of the night sky are the patterns made by the stars.

• The familiar shapes became constellations, made to look like familiar objects.

• Different cultures saw these patterns differently. We use the system starting with the Babylonians.

The Stars are “Fixed”They don’t change over time.

Leo the Lion

Like the Sun, they move across the sky from

east to west.

E W

Some constellations revolve around a single point…

Polaris

This single point is true north,and it is used for navigation.

The Drinking Gourd, or “the Dippers,” used by Freedom Seekers escaping slavery.

Seafaring people, like

the Polynesians discovered

that the height of stars

change with latitude.

How the Polynesians navigated…

• They knew that they could sail from Fiji to Tahiti if they kept Sirius overhead.

• If they sailed north, eventually Arcturus (Hokule’a) would be at the top of the sky.

• Then they were on their way to Hawaii.

We see different constellations in winter than in summer…

WINTERSUMMER

This was accurately recorded by Chinese observers around 5000

years ago.

Planets

• While constellations kept their shapes, several objects appeared to wander among them.

• These strange objects were the planets.

• They travel through the constellations of the zodiac.

Venus

The Conjunction of Venus, Saturn, and Mars 2010

June 20

July 4

July 22

July 27Aug. 4Aug. 10Aug. 14Aug. 20

Five such wandering planets were known to ancient people:

Venus, Mars, Jupiter, Saturn, Mercury.

Why didn’t they consider Earth to be a planet?

Venus in particular was tracked by both Babylonians and Mayans

““Shooting Stars”Shooting Stars”

• Several times a year , the sky explodes with “shooting stars” or meteor showers.

• What causes these strange events?

• They have nothing to do with stars, but are caused by small particles falling through the Earth’s atmosphere.

Then there were unexpected events, like comets.

The universe turns out to be rather complicated.

What was needed next was someone to make sense out of all this commotion.

That happened in Greece.