what are stars? huge, hot balls of gas that are trillions of kilometers away from the earth
TRANSCRIPT
• 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.
• 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
•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
•Stars are classified by HOW HOT THEY ARE!
•Temperature differences between stars result in COLOR DIFFERENCES
•Hottest stars are BLUE
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.