Ch.18.1 Astronomy: The Original Science!

P.5541) Please take a copy of this unit standards

and glue it in your IAN.

2) Next, copy down today’s lesson title.

3) EQ: Imagine that it is 5,000 yrs ago. Clocks and calendars have not been invented yet. How would you tell the

time or know what day it was?

History of Astronomy

The guys with their eyes on

the skies!!

• People in ancient cultures used the seasonal cycles of the stars, planets, and the moon to mark the passage of time. For example, by observing these yearly cycles, early farmers learned the best times of year to plant and harvest various crops.

• Over time, the study of the night sky became the science of

astronomy. Astronomy is the study of the universe. Although ancient cultures did not fully understand how the planets, moons, and stars move in relation to each other, their observations led to the first calendars.

Mayan

Greeks: Aristotle

Background info:

• At eighteen, he joined Plato's Academy in Athens and remained there until the age of thirty-seven (c. 347 BC). His writings cover many subjects – including physics, biology, zoology, metaphysics, logic, ethics, aesthetics, poetry, theater, music, rhetoric, linguistics, politics and government

• Aristotle knew that the earth was a sphere. -each part of the earth is trying to be pulled to the center of the earth, and so the earth would naturally take on a spherical shape.

• the shadow of the earth on the moon during a lunar eclipse was always circular. The only shape that always casts a circular shadow is a sphere.

• as one traveled more north or south, the positions of the stars in the sky change. There are constellations visible in the north that one cannot see in the south and vice versa.

Aristotle: Earth is a Sphere!

Claudius Ptolemy •140 AD•further developed the geocentric model (Earth-centered)

•planets move on small circles that move on bigger circles – explained why Mars moved backward

•accepted for 1,500 years

E

M

epicycles

What happened next?

Nicolaus Copernicus•Early 1500's•developed heliocentric model (sun-centered)

•Used geometry to determine Earth to Sun distance and the planets arrangement/movement

•Still thought orbits were perfect circles

Tycho Brahe• late 1500's• believed much of what

Copernicus observed, except that planets travel on orbits that are perfect circles

• his team observed and recorded the positions of the planets for more than 20 years

Brahe used a mural quadrant, which is a large quarter-circle on a wall, to measure the positions of stars and planets.

sun

Johannes Kepler

•1600's•One of Brahe’s assistants

•proved that orbits were NOT perfect circles: they are ellipses

Galileo Galilei•Early 1600's•Changed lenses in telescope to mirrors

•Using the telescope he proved the heliocentric model with the following discoveries:

4 moons orbiting Jupiterphases of Venuscraters on the Moon

Sir Isaac Newton

•1665•explained why the planets stay moving around the sun: inertia and gravity

•1st law: inertia-a body will continue in a straight line unless acted on by a force.

•Gravity keeps the moving planets in orbit around Sun

Modern AstronomyThe invention of the telescope and the description of gravity were two milestones in the development of modern astronomy. In the 200 years following Newton’s discoveries, scientists made many discoveries about our solar system. But they did not learn that our galaxy has cosmic neighbors until the 1920s.

Edwin Hubble: Beyond the Edge of the Milky WayBefore the 1920s, many astronomers thought that our galaxy, the Milky Way, included every object in space. In 1924, Edwin Hubble proved that other galaxies existed beyond the edge of the Milky Way. His data confirmed the beliefs of some astronomers that the universe is much larger than our galaxy. Today, larger and better telescopes on the Earth and in space, new models of the universe, and spacecraft help astronomers study space. Computers help process data and control the movement of telescopes. These tools have helped answer many questions about the universe. Yet new technology has presented questions that were unthinkable even 10 years ago