STARS

Amy Johnson

In General

Stars are always in the sky, but can only be seen at night when the atmosphere is not so brightThe Sun is the closet star to Earth.Stars appear to move across the sky at night due to the rotation of Earth on its axis.Star patterns in the night sky change seasonally due to its revolution.

Constellations

A group of stars that form patterns in the sky

Most visible• Ursa Major-Big Dipper• Ursa Minor-Little Dipper

Starry Colors and Size

Color gives clue to the temperature of the star

Red is the coolest of the visible starsYellow stars are medium temperatureBluish-white are the hottest stars

Most stars are smallSun is a medium starBetelgeuse – would swallow the first four planets

Apparent Magnitude

A system used in classifying the brightness of a star from EarthThe smaller the number, the brighter the star

Sirius, the brightest star, measures a -1.5Sun measures a –26.7

The sun looks brighter due to its location to Earth

The Life of a Star - Birth

Begin as gas and dustGravity causes dust and gas to move close togetherTemperatures rise and cause atoms in cloud to mergeProcess called fusion and changes matter to the energy that powers the star

The Life of a Star - Evolving

Small and medium stars use up the gases in the core and become a giant star

Large, cool stars, red in colorSun will become a giant in 5 billion years• Will cover orbit of Mercury, Venus and

Earth• Will be a giant for a billion years

Evolving

Large stars become supergiantsCore collapses, shock wave, explosion, becomes brighter• Explosion known as a supernova• Might shine more brightly than entire galaxy• Released dust and gas may become part of a

new star

If core remains, it becomes a neutron starIf core collapses rapidly, a black hole forms

The Life of a Star - Death

The outer shell of the star will be lostThe core shrinks and is known as a white dwarf

White dwarfs are hot and small

Eventually, white dwarfs cool and stop shining – black dwarf

Galaxies

A group of stars, gas, and dust held together by gravityElliptical

Very common, football shaped

SpiralGiant pinwheel, some with bar-shaped

IrregularCommon, smaller, not easily classified

Galaxy contents

Nebulas- clouds of gasGlobular clusters- groups of old starsOpen clusters- stars on the spiral disk, newly formed blue stars

Milky Way

Giant, spiral galaxyContains hundreds of billions stars, including the SunStars revolve around the center of galaxies

once every 225 million years the Sun makes a revolution

What We See

Only part of the Milky Way is visible due to our being in the galaxyGalileo saw the Milky Way in 1609 using a telescope

Bigger and brighter than most galaxies in the universe

Special stars

Supernova - an exploding starNeutron star- remainder of supernovaPulsars-spinning neutron starQuasars- galaxies in the process of forming, incredibly brightBlack hole- beyond pulsar that does not allow anything to escape

Speed of Light

Light travels through space 300,000 km/s

Around Earth 7 times in one second

You cannot go faster than lightLight-years measures distances between galaxies since the distance is so vast

The distance light travels in one year = light year (9.5 trillion km)

Universe

Galaxies contain billions of starsBillions of galaxies make up a universeIn 1995, the Hubble Space Telescope discovered over 1,500 galaxies in a tiny sector of the sky