WHAT ARE STARS?•Huge, hot balls of gas that are trillions of kilometers away from the Earth.

• Astronomers study the COLOR of star light

• Which color is the hottest? • Red and yellow – cool• Blue - hot

• Spectrum – when you look at white light through a glass prism – see a rainbow of colors (ROYGBIV)

• Continuous Spectrum – shows all the colors – a hot, solid object, such as the glowing wire inside a light bulb

• A Spectrograph is used to break a star’s light into a spectrum

• This gives information about COMPOSITION and TEMPERATURE of a star

•For example – when look at a neon sign WOULD NOT see a continuous spectrum but would see EMISSION LINES

•Emission Lines are lines made when certain wave lengths of light or COLORS are given off by hot gases

•Bright Line (Emission)-A spectrum consisting of individual lines at unique spots.

CONTINUOUS SPECTRUM

BRIGHT EMISSION LINES

• Each element has a unique set of bright emission lines.

• A Star’s Spectrum is made up of DARK EMISSION LINES

• A star’s atmosphere absorbs certain colors of light in the spectrum, which causes black lines to appear!

AbsorptionDARK EMISSION LINES

• ABSORPTION SPECTRUM - a star’s atmosphere absorbs colors of light instead of emitting them

•An absorption spectrum is produced when light from a hot solid or dense gas passes through a cooler gas.

•Absorption spectrum of a star – inside is hotter than it’s atmosphere

•Black lines in a spectrum represent where less light gets through

•What is this star made of?

Hydrogen

Helium

•Stars are classified by HOW HOT THEY ARE!

•Temperature differences between stars result in COLOR DIFFERENCES

•Hottest stars are BLUE

•TYPES OF STARS

Temperature & Color

• Stars can be different colors• Reddish stars are coolest

(<4000°C)

• Orange/Yellow stars are medium (4000°-7000°C)

• White & Blue stars are hottest(7000°-30,000°C)

• Brightest stars – 1st MAGNITUDE STARS

• Dimmest stars – 6th MAGNITUDE STARS

• Positive numbers – dimmer stars• Negative numbers – brighter stars

Apparent Magnitude

•How bright stars look when they’re viewed from Earth

•Low numbers are brightest, high are dimmest

•Sun = -26.7•Sirius = -1.45 (Brightest Star)

Absolute Magnitude

•The ACTUAL BRIGHTNESS OF A STAR

•If all stars were the same distance away, their absolute magnitudes would be the same as their apparent magnitudes.

Absolute Magnitude

• The brightness that a star would have at a distance of 32.6 light years from Earth

•Sun = +4.8 (ordinary for a star)•Due to closeness to Earth

Sun’s apparent magnitude is -26.8

DISTANCE IN SPACE1. LIGHT YEARS – distance that

light travels in one year – 9.5 trillion kilometers (light moves 300,000 Km/sec)

2. PARALLAX – an apparent shift in the position of an object when viewed from different directions

• Notice that the location of the middle star seems to shift in relation to more distant stars – seen through telescopes

• Daytime and nighttime are caused by the Earth’s rotation

• The apparent motion of the sun and stars in our sky is due too the EARTH’S ROTATION

• The Earth’s tilt and revolution around the sun cause the seasons.

• During each season the Earth faces a different part of the sky at night.

• All stars that we see appear to rotate around POLARIS (the North Star)

• Due to the Earth’s rotation all of the stars in the sky appear to make one complete circle around Polaris every 24 hours.