Stars and galaxies

Constellations  Ancient Greeks, Romans and other cultures saw patterns of stars in the sky called constellations  They imagined they represented mythological characters, animals or familiar objects.  Stars in constellations have no relationship to each other in space.

Modern constellations  The sky is now divided into 88 constellations  Many were named by ancient astronomers

Circumpolar constellations  Many constellations circle the North star, Polaris – Big Dipper, Little Dipper, Cepheus, etc.  Polaris is directly above the North pole  Constellations appear to move because of the Earth’s rotation  As Earth orbits the Sun, different constellations come into view. While others disappear (Orion is only seen in winter)  Circumpolar const. are visible all year

Absolute and apparent magnitude  some stars seem brighter than others, but that doesn’t mean they are closer to us or are really brighter  A star that is very dim might appear bright in the sky if it’s close to Earth, and a star that is very bright might appear dim if it is far away

Measurement in space  Measuring a star’s parallax tells us the distance to stars from our solar system  Scientists measure the apparent shift of an object from two different positions.  The closer an object is to Earth, the greater the parallax

 We use light years to measure distance in space because space is so huge  Light travels 300,000 km/s or about 9.5 trillion km in one year  The nearest star to Earth, other than our Sun, is Proxima Centauri, which is 4.3 light years away, or 40 trillion km

Properties of stars  The color of a star tells us its temperature  Astronomers study star properties by looking at their spectra.  Light from a star passes through a spectroscope which breaks the light into all the colors of the spectrum  Dark lines in the spectra tell scientists which elements are in a stars atmosphere