Why Astronomy?
For countless centuries, humans have wondered about objects they saw in the sky and worried about
how they affected their lives.
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?
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.
This single point is true north,and it is used for navigation.
The Drinking Gourd, or “the Dippers,” used by Freedom Seekers escaping slavery.
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.
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?
““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.