Stars, starlight AND Light Information

OUTCOME QUESTION(S): S1-4-06: How do astronomers measure the great distances in the universe? S1-4-07: What can an astronomer learn about a star by looking at light? Vocabulary & People Astronomical UnitLight-year Apparent magnitude Absolute magnitude Electromagnetic Energy Spectroscope

Scientific Notation (x 10 X ) Express very large or very small numbers “Power of 10” equals the number of places the decimal was moved (+) large, (-) small is 3.2 x is 5.5 x x 10 5 is x is A negative exponent (10 -5 ) means divide by 10 that many times A positive exponent (10 7 ) means multiply by 10 that many times

Distance and the Universe Common to use Astronomical Unit (A.U.) 1 A.U. = distance between the Earth and the Sun Earth to the Sun: 1 AU = 1.5 x 10 8 km ( ) Common Distances: Sun - Pluto: ~ 40 AU Sun - Saturn: ~ 10 AU Sun - Jupiter: ~ 5 AU Sun - Mars: ~ 1.5 AU So Pluto is 40x farther away from the Sun than Earth

Nearest star x km away from Earth! This star is Proxima Centari Light-year (LY): The distance a beam of light travels in one year Light moves outward fast – about 300,000 km/sec x km /year = 1 light-year P. Centari is 4.3 light-years away That’s 41,000,000,000,000 km!

Distances can be deceiving: Bright stars look close, but may be very far away Star Approx. Distance (LY) P. Centari4.3 Sirius 8.8 Betelguese 700 Rigel 900 Most distant known galaxy15,000,000,000 Star light takes years to get to Earth – this delay means we are looking at old “images” – it’s like looking into the past…

Luminosity (brightness) There are two amounts (magnitudes) of brightness: Apparent magnitude – brightness as we see it. Absolute magnitude – actually brightness. The Sun has a higher apparent magnitude, since it is so much closer than other stars Star light can be used to determine temperature, composition and size (mass)

Star B looks brighter – more apparent magnitude Star B is closer to us than Star A Star B and A have the same absolute magnitude

Temperature of Colour Colour – shows how much energy a star emits. Colder star glows red Hotter star glows bluish white or even blue ColourTemperature ( o C)Example Blue25,000 – 50, 000 Bluish-white11,000 – 25,000Rigel (Orion’s belt) White7,500 – 11,000Sirius (brightest) Yellowish-white6,000 – 7,500Polaris Yellow5,000 – 6,000Sun Orange3,500 – 5,000 Red2,000 – 3,500P. Centauri (closest) Despite being cooler, the Sun is still bigger than about 95% of stars

Notice bigger stars are not necessarily hotter…but usually brighter

Star Composition Scientists use a spectroscope to analyse the light energy coming from stars Light is a type of energy called: Electromagnetic Energy Spectroscope – tool that splits light into a pattern of colours, like a rainbow.

The black lines in the spectrum are used to identify the elements that make up the star. The elements that make the star will absorb unique parts of the spectrum as energy is released. Showing as the “black” lines of missing energy

Remember your chemistry: heated compounds give off a unique colour spectrum. Scientists have heated elements and recorded the unique light energy patterns The “missing” black lines in the spectra of the Sun match with the known spectra of Hydrogen but not with Mercury – so the Sun contains Hydrogen!

CAN YOU ANSWER THESE QUESTIONS? S1-4-06: How do astronomers measure the great distances in the universe? S1-4-07: What can an astronomer learn about a star by looking at light? Vocabulary & People Astronomical UnitLight-year Apparent magnitude Absolute magnitude Electromagnetic energySpectroscope