Chapter 1: Stars and GalaxiesChapter 1: Stars and Galaxies

When you look up at the sky on a When you look up at the sky on a clear night, you see billions of stars clear night, you see billions of stars in the sky. Each star is actually a in the sky. Each star is actually a sun! A sun! A sunsun is hot sphere of glowing is hot sphere of glowing gas.gas.

Our sun is a Our sun is a single-starsingle-star system, system, however most of the stars in the however most of the stars in the sky are sky are double-stardouble-star systems in systems in which 2 stars revolve around each which 2 stars revolve around each other. These are called other. These are called binary binary starsstars..

ConstellationsConstellations are groups of stars are groups of stars that were once believed to be that were once believed to be imaginary people or animals.imaginary people or animals.

ExamplesExamples: Big Dipper, Orion, : Big Dipper, Orion, HerculesHercules

A A novanova is when a sun suddenly is when a sun suddenly increases in brightness due to a increases in brightness due to a nuclear explosion. Nova’s release nuclear explosion. Nova’s release gas, heat, and light into space.gas, heat, and light into space.

A huge cloud of dust and gas A huge cloud of dust and gas where new stars are formed is where new stars are formed is called a called a nebulanebula..

A huge collection of stars is A huge collection of stars is collectively known as a collectively known as a galaxygalaxy. Our . Our galaxy is named the galaxy is named the Milky WayMilky Way..

The The Big-Bang TheoryBig-Bang Theory states that our states that our universe began as one large mass that universe began as one large mass that exploded and gave rise to our modern-exploded and gave rise to our modern-day planets. day planets.

According to this theory, all the According to this theory, all the mattermatter and and energyenergy in the universe was once in the universe was once concentrated into a concentrated into a singlesingle place. About place. About 15-20 billion years ago, an explosion 15-20 billion years ago, an explosion sent matter and energy in all sent matter and energy in all directions.directions.

Astronomers estimate that there Astronomers estimate that there are more than are more than 200 billion200 billion stars in stars in the universe! the universe!

Stars differ in: size, mass, color, Stars differ in: size, mass, color, temperature, and brightnesstemperature, and brightness

SIZES OF STARS...SIZES OF STARS...

1. 1. Giant starsGiant stars: 10-100 times the size : 10-100 times the size of our sunof our sun

2. 2. Supergiant starsSupergiant stars: 1000 times the : 1000 times the sizesize

3. 3. White dwarfWhite dwarf: smaller than Earth: smaller than Earth4. 4. Neutron starNeutron star: the smallest star: the smallest star

The elements Hydrogen (H) and The elements Hydrogen (H) and Helium (He) make up 96-99% of a Helium (He) make up 96-99% of a star’s mass.star’s mass.

BRIGHTNESS OF STARS...BRIGHTNESS OF STARS...

Apparent MagnitudeApparent Magnitude refers to the refers to the brightness of a star as it appears on brightness of a star as it appears on Earth.Earth.

Absolute MagnitudeAbsolute Magnitude refers to the refers to the actual amount of light that a star gives actual amount of light that a star gives off.off.

THE SUN...THE SUN...

Our sun is 150 million kilometers Our sun is 150 million kilometers from the Earth. It is an average-from the Earth. It is an average-sized star, about 4.6 billion years sized star, about 4.6 billion years old.old.

The sun’s volume is 1 million times The sun’s volume is 1 million times the size of Earth!the size of Earth!

LAYERS OF THE SUN...LAYERS OF THE SUN...CoronaCorona: outermost layer of the sun’s : outermost layer of the sun’s

atmosphere, 1.7 million degrees Celsius! atmosphere, 1.7 million degrees Celsius! (white halo)(white halo)

ChromosphereChromosphere: beneath Corona, average : beneath Corona, average temp. of 27,800temp. of 27,800 C C (middle layer of the Sun’s atmosphere)(middle layer of the Sun’s atmosphere)

PhotospherePhotosphere: referred to as the sun’s : referred to as the sun’s surface, temp. of 6000surface, temp. of 6000 C C

CoreCore: innermost part, up to 15 million : innermost part, up to 15 million degrees C, site of degrees C, site of nuclearnuclear fusionfusion (H + H (H + H He)He)

Solar FlareSolar Flare: a “storm” on the sun, : a “storm” on the sun, temperature increases, large temperature increases, large amounts of energy are released.amounts of energy are released.

SunspotsSunspots: dark spots that are seen : dark spots that are seen on the sun’s surface, cooler than on the sun’s surface, cooler than the rest of the sun.the rest of the sun.

SUPERNOVASUPERNOVA......When the nuclear fusion reaction is When the nuclear fusion reaction is

finished, the sun explodes in a finished, the sun explodes in a tremendous release of energy called a tremendous release of energy called a SupernovaSupernova. When this happens, . When this happens, temperatures of temperatures of 1 billion degrees C1 billion degrees C are are released! released!

BLACK HOLES...BLACK HOLES...

After a star burns out, or supernovas, a After a star burns out, or supernovas, a core where the star used to be remains. core where the star used to be remains. This is called a This is called a black holeblack hole. Here, . Here, gravity produced pulls matter and gravity produced pulls matter and energy inward and eventually is energy inward and eventually is swallowed. swallowed.