Stars Constellations -Patterns of stars in the sky A constellation looks like spots of light arranged in a particular shape against the dark night sky. Example you can find the star Betelgeuse on the right shoulder of mighty hunter Orion. The North Star, also known as, Polaris, is located at the end of the Little Dipper in the constellation Ursa Minor. Polaris is positional almost directly over Earths north pole. Circumpolar Constalletions As the Earth rotates, Ursa Major, Ursa Minor and other constellations in the northern sky circle around Polaris. The stars seem to complete one full circle in less than 24 hours. Absolute and Apparent Magnitudes When you refer to the brightness of a star, you can refer to its absolute magnitude or its apparent magnitude. Absolute magnitude- a measure of the amount of light it gives off Apparent magnitude- a measure of the amount of light received on Earth Summary A star may be dim in brightness, but seem bright because it is close to the Earth. A star that is bright may look dim because it is very far from the Earth. Light bulb example How do scientist determine distance to stars They use parallax ( the apparent shift in the position of an object when viewed from two different positions). (thumb example) Scientists use the angle that the stars position changes, and the size of the Earths orbit to calculate the distance of the star from Earth. Light-year: is the distance that light travels in one year Light travels at 300,000 km/s or about 9.5 trillion km in one year. Nearest star other than the Sun to Earth is Proxima Centauri, which is 4.3 light years away or about 40 trillion km. Properties of Stars The color of a star indicates its temperature. Hot stars- > blue-white color Cool stars-> orange or red color Stars w/ the same temp as the sun -> yellow color Spectroscope- scientific instrument that measures the intensity of light, wavelengths Spectra- light that is spread out into a rainbow band Hertzsprung-Russell (H-R) Diagram The Diagram places temperatures of stars at the bottom and the absolute magnitudes up one side. Colors of Stars The Main Sequence -A diagonal band that runs from the upper left to the lower right of the H-R Diagram. It contains hot, blue, bright stars in the upper left and cool, red, dim stars in the lower right. Yellow stars, like the sun, fall in between. Contains 90% of all stars. Dwarfs and Giants White Dwarfs- small stars located on the lower left of the H-R diagram. (very hot w/ low absolute magnitude) Giants- large stars on the upper right of the H-R diagram (aka: red giants) usually red in color Super Giant- largest giants on the top of the H-R diagram Question What type of stars are on the main sequence? Fusion Occurs in the cores of stars. 1.Atoms start to fuse when temperatures in the core of stars gets high enough. - Atoms move so fast that some of them fuse upon colliding Properties of Stars