Introduction to Astronomy

What is astronomy?

• Astronomy is the science that studies the universe. It includes the observation and interpretation of planets, stars, and other bodies in space.

http://science.howstuffworks.com/telescope.htmImage credit: NASA / Apollo 8 crewmember Bill Anders.

Early astronomy (Those Ancient Greeks! Yes they were very smart. Observed the heavens, applied philosophy)Aristotle popularized the…•Geocentric model of the universe:– Geo = __________ centr = __________– Earth is the center of the universe; the sun and

other plants revolve around it

Aristotle (the guy in Carolina blue), as painted by Raphael

Why do the planets sometimes move backwards?

• Early astronomers observed:– planets move eastward against the background of stars.– Sometimes the planets seemed to stop, reverse

direction, and then later carry on eastward.

• This apparent westward (backward) motion of the planets is called retrograde motion– Important! because it made them question the geocentric

model

Retrograde motion of Mars

East West

Sept.

Aug. July

June

Dec.Jan.Feb.March

AprilMay

(really puzzling)

Retrograde MotionAnimation

Birth of modern astronomy

• Nicolaus Copernicus– Earth is a planet– proposed the…

• Heliocentric model of the solar system– Helio = __________ centr = __________– Sun is the center of the solar system, planets

revolve around it (including Earth)– better explained retrograde motion

http://www.universetoday.com/33113/heliocentric-model/

Nicolaus Copernicus

Kepler’s Laws of Planetary Motion

• Kepler used Brahe’s observations to develop 3 laws to explain the movement of the planets

– 1st Law: Planets move in elliptical (oval) orbits around the sun

– 2nd Law: Planets move faster when they are closer to the sun

Planet revolution 1st & 2nd Law Animations

Kepler’s Laws of Planetary Motion

• Kepler used Brahe’s observations to develop 3 laws to explain the movement of the planets

– 1st Law: Planets move in elliptical (oval).orbits around the sun

– 2nd Law: Planets move faster when they are closer to the sun.

– 3rd Law: The further the planet is from the sun, the longer its orbital period (p2=a3)

• orbital period is the time (in Earth years) it takes a planet to go once around the sun.

3rd Law Animation

Galileo’s telescope

• Galileo improved on the “new” invention… the telescope

• Amazing discoveries in great detail• Detailed records of the heavens

http://news.nationalgeographic.com/news/2009/08/photogalleries/galileos-telescope-pictures-anniversary/

Sir Isaac Newton: one heavy dude• Developed a formula to explain gravity, now

called the law of universal gravitation– All objects with mass have a gravitational pull– The greater the mass of an object, the greater is

its pull on other objects– The pull decreases with distance– Meaning for the planets?– Tennis ball demo

Gravity

Gravity’s influence on orbits

Motions of Earth

• Rotation– The turning, or

spinning, of a body on its axis

– Responsible for our days and nights (why?)

– One complete earth rotation (one noon to the next) is about _____ hours

http://www.physicalgeography.net/fundamentals/6h.html

Motions of Earth

• Revolution– The motion of a body, such as a planet or

moon, along a path around some point in space (in this case, the sun)

– One complete earth revolution is about _____ days

– Perihelion is the time in Jan when Earth is closest to the sun; aphelion is the time in July when Earth is farthest from the sun

– Volunteer ?

http://science-class.net/Notes/Notes_Seasons_7th.htm

Motions of Earth

• Precession– The change in the

direction in which the axis of the Earth points

– Earth’s “wobble”– One complete cycle

occurs about every _____ years

– In 13,000 years (half-way), Polaris will no longer be our “North Star.”; instead it will be the star Vega (and summer will be winter)

http://www.dreamstime.com/royalty-free-stock-images-spinning-top-toy-image15214709

Volunteer?

Precession Animation

Why do we have seasons?

• Earth’s tilt on its axis, along with its revolution around the sun causes the seasons!– As Earth moves around the sun, the tilt

changes the angle of light received from the sun

– Light hitting at direct angle = summer– Light hitting at indirect angle = winter

http://education.arm.gov/teacher-tools/lessons/reason

Earth’sSeasons

Phases of the moon

• The moon revolves around Earth– One complete revolution is about _____ days

• The moon changes shape (phase) because of the changing amount of sunlight reflected off the moon– These changes occur monthly

Phases of the Moon

YouTubeSong

Moon Phases Animation

What is a blue moon?

Phases of the Moon

Motions of the moon

• The moon’s period of rotation on its axis and its revolution around Earth are the same (about a month)

• SO… we always see the same side of the moon

• volunteer?

Why We SeeThe Same

Side ofThe Moon

Eclipses

• Normally the moon orbits about 5 degrees off the earth-sun orbital plane

• At special times of the year, the earth, moon, and sun “line up”

• Solar eclipse: when the moon is directly between Earth and the sun, casting a shadow on part of Earth.

Solar Eclipse

What phase is the moon in during a solar eclipse?… and what time of day?

Solar Eclipse

Solar eclipseEclipses For 2013

Eclipses

• Normally the moon orbits about 5 degrees off the earth-sun orbital plane

• At special times of the year, the earth, moon, and sun “line up”

• Solar eclipse: when the moon is directly between Earth and the sun, casting a shadow on part of Earth.

• Lunar eclipse: when Earth is directly between the moon and the sun, casting a shadow on the moon.

Lunar Eclipse Lunar eclipse

What phase is the moon in during a lunar eclipse?…and what time of day?

Origin of the moon

• Most widely accepted theory…• When the solar system was forming, a

body the size of Mars hit Earth. The resulting debris was thrown into space, began orbiting around Earth, and eventually united to form the moon.

Origin of the moon

Why is the moon so important?

• The moon calms Earth’s tilt; controls our tides, and so much more!

• While watching the movie, describe at least 10 ways our Earth would be different if we had no moon (page 17 in your notebook)

The Day the Moon Was Gone

(YouTube)

Pt.1: start @ 43.24

The Day the Moon Was Gone

(Amazon)

Pt.1: start @ 43.24

Your summary

• Discuss with your table partner about what you will write in your summary box– Should be 1-3 sentences giving the major points

of the Intro Astronomy notes

• … then write your summary!