Unit 2: AstronomyUnit 2: Astronomy

I. HistoryI. History

• Astronomy: study of the planets, stars, and other objects in spaceA. Nicolaus Copenicus: Polish astronomer, first suggested the sun was the

center of the solar system and put six known planets in proper orderB. Galieo Galilei: Italian scientist whose greatest contributions were his

descriptions of moving objects1. Laid groundwork for the study of gravity by demonstrating that the weight of an

object does not affect its rate of fall2. Discovered four moons of Jupiter; observed and recorded the phases of Venus;

studied the moon’s surface; tracked sunspots3. Tried by Inquisition in the 1600’s for teaching against the current belief of the

Catholic Church (sun was center of the universe); declared innocent by John Paul II in the 1980’s

C. Albert Einstein: A German-born American physicist, developed the theory of relativity to explain motion of particles traveling at the speed of light

D. Edwin Hubble: American astronomer, first discovered light beyond our galaxy

II. Instruments of AstronomyII. Instruments of Astronomy

A. Refracting telescope: telescope that uses a series of lenses to gather and focus visible light from distant objects

B. Reflecting telescope: telescope that uses a series of mirrors to gather and focus visible light from distant objects

C. Radio telescope: telescope that gathers radio waves from distant objects in order to produce images of those objects1. Grote Reber built first in 19392. Can be used day and night, in any weather3. Quasars and pulsars: two radio energy sources discovered with radio

telescopeD. Spectroscope: instrument that breaks up light into its characteristic

colorsE. RADAR: system that detects an object beyond the range of visible

light; determines the object’s distance or range

III. Distances in AstronomyIII. Distances in Astronomy

A. Astronomical unit (AU): the average distance between the Earth and the sun

1. 150 km (93 million miles)2. Used for measurement within the solar

system

B. Light year: distance light travels in a year1. 8 min. for light to reach Earth from sun2. Used to measure distances to stars and

beyond

IV. OriginsIV. Origins

A. Universe1. Big Bang Theory: theory that states that the

universe began to expand with an explosion of concentrated matter and energy and has been expanding ever since

B. Solar system1. Nebular Theory: theory that the solar system

began as a huge cloud of dust and gas called a nebula, which later condensed to form the sun and its nine planets

V. SunV. Sun

• Sun: a medium size yellow star composed mostly of hydrogen and helium; exerts gravity on planets holding them in orbit

A. Rotates once each month

B. Revolves around Milky Way Galaxy every 225 million years

C. 109 times the size of Earth

V. Sun (cont.)V. Sun (cont.)

A. Structure1. Core: nuclear fusion occurs here, hottest part2. Radiative zone: very dense zone3. Convective zone: gases circulate in convection currents4. Photosphere: innermost layer of the sun’s atmosphere5. Chromosphere: deep red, seen during a total eclispe6. Corona: outermost layer of the sun’s atmosphere

B. Solar Activity1. Sunspots: dark areas on the sun’s surface2. Solar flares: storms on the sun that show up as a bright burst of

light on the sun’s surface3. Prominences: violent storms on the sun that can be seen from

Earth as huge bright arch or loop of hot gas

VI. PlanetsVI. Planets

VII. CometVII. Comet

• Comet: object made of ice, gas, and dust that travels through space

A. Orbit the sun in an elliptical orbit, have varying periods of revolution, ex. Halley’s appears every 76 years, next 2061

B. Originate in an area outside our solar system; possibilities include Oort cloud and Kuiper belt

C. Tail: as comet approaches sun the heat vaporizes parts of it, solar wind and energy force the particles to stream away from the sun

VIII. AsteroidsVIII. Asteroids

• Asteroids: small, rocky bodies orbiting the sun in same direction as the planets

A. Most are found in a region between Mars and Jupiter

B. Believed to be fragments of pre-planet material

C. Some cross Earth’s orbit

IX. MeteoroidsIX. Meteoroids

• Meteoroid: chunk of metal or stone that orbits the sun

A. Meteor: streak of light produced by a meteoroid as it burns up in the Earth’s atmosphere

B. Meteorite: meteor that strikes the Earth’s surface

C. Meteor showers: occur when Earth passes through debris left in a comet’s orbit

X. StarsX. Stars

• Stars: bright spheres of gases; energy is produced by nuclear fusion

A. Properties1. Magnitude: the brightness of a star depends on its composition

and distance from Eartha. Absolute: amount of light a star actually gives offb. Apparent: brightness of a star as it appears on the Earth

2. Color and temperature are relateda. hot-blueb. cooler-redc. medium-yellow

3. Hertzberg-Russell diagram: chart that shows the relationship between the absolute magnitude and the surface temperature of stars

X. Stars (cont.)X. Stars (cont.)

B. Life cycle1. Nebula: massive cloud of dust and gas between the stars2. Protostar: new star3. Main sequence: hydrogen changes to helium, may last for billions of

years depending on mass4. Red Giant: star’s outer surface cools, expands and becomes red5. Death: final stage depends on mass

a. Low mass: red giant collapses and becomes white dwarfb. Medium mass: forms planetary nebula than white dwarfc. Massive mass: supernovas, then may become a very dense neutron star or

and extremely dense black hole

C. Other stellar objects1. Pulsar: neutron star that gives off pulses of radio waves2. Quasar: quasi-stellar radio source; distant object that gives off mainly

radio waves and x-rays

X. Stars (cont.)X. Stars (cont.)

D. Constellations: groups of stars that form a pattern1. Used in the past for navigation and as a yearly

calender2. Circumpolar: five constellations seen throughout the

year, rotate around the North Star, include:a. Ursa Major, the Great Bear, part of which is the Big Dipper;

stars at the end of its bowl point to the North Starb. Ursa Minor, the Little Bear or Little Dipper; Polaris, the

North Star is at the end of its handle

3. Zodiacial constellations: band of twelve constellations moving across the sky throughout the year

X. Stars (cont.)X. Stars (cont.)

E. Galaxies: huge collection of stars1. Spiral: galaxy that is shaped like a pinwheel; one of three types

of galaxies2. Elliptical: galaxy that may vary in shape from nearly spherical to

flat3. Irregular: no regular shape, many stars, great clouds of gas and

dusta. Large Magellanic Cloudb. Small Megellanic Cloud: both seen from the Southern Hemisphere

F. Other star groups1. Globular clusters2. Open clusters3. Nebulas