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Ch.1, Sec.3 - Mapping the Stars Patterns in the Sky constellation: a region of the sky that contains a recognizable star pattern and that is used to describe the location of objects in space - every star or galaxy is located within 1 of 88 constellations - as seasons change on Earth, the visibility of certain constellations change too - visible constellations are different in the Southern Hemisphere as compared to the Northern Hemisphere Ch.1, Sec.3 - Mapping the Stars Finding Stars in the Night Sky - the use of an astrolabe helps show the location of a star or planet - three points of reference need to be used: zenith, altitude, and horizon Ch.1, Sec.3 - Mapping the Stars zenith: an imaginary point in the sky directly above an observer on Earth (the zenith always has an altitude of 90˚!) altitude: the angle between the object and the horizon horizon: the line where the sky and the Earth appear to meet Ch.1, Sec.3 - Mapping the Stars - astronomers also use the celestial sphere model to locate stars (see figure 5 on pg. 17) - circumpolar stars are stars that can be seen at all times of year and at all times of night - in the Northern Hemisphere, ______________ is the most famous Polaris circumpolar star - in the Southern Hemisphere, Sigma Octantis is the most famous circumpolar star Ch.1, Sec.3 - Mapping the Stars The Size and Scale of the Universe - stars are much farther than planets and we use the lightyear to measure their distance from us - one light-year represents the distance light travels in 365 days (6 trillion miles @ 186,000 miles per second) Proxima Centauri is the closest star to our solar system at 4.2 light years away! Epsilon Eridani b is the closest planet to our solar system at 10 light years away! Ch.1, Sec.3 - Mapping the Stars - There are 100 billion galaxies in the observable Universe. When you put those numbers together, you get an estimate of 1024 stars in the entire Universe or a 1 followed by 24 zeroes (called one septillion)! That’s 1,000,000,000,000,000,000,000,000 stars or more than all the combined grains of sand on planet Earth!!!! Ch.1, Sec.3 - Mapping the Stars - The Andromeda Galaxy is the closest spiral galaxy to the Milky Way at just over 2.5 million light-years away. Ch.1, Sec.3 - Mapping the Stars The Doppler Effect - redshift occurs because objects moving faster away from Earth emit a redder light - blueshift occurs because objects moving faster towards Earth emit a bluer light - everything is expanding in the Universe!!! Ch.1, Sec.3 - Mapping the Stars - evidence of redshift from the Hubble Ultra Deep Field image Ch.1, Sec.3 - Mapping the Stars