Ch.1, Sec.3 - Mapping the Stars Patterns in the Sky 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 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 circumpolar star - in the Southern Hemisphere, Sigma Octantis is the most famous circumpolar star Polaris

Ch.1, Sec.3 - Mapping the Stars The Size and Scale of the Universe The Size and Scale of the Universe - stars are much farther than planets and we use the light- year to measure their distance from us - one light-year represents the distance light travels in 365 days (6 trillion 186,000 miles per second) Epsilon Eridani b is the closest planet to our solar system at 10 light years away! Proxima Centauri is the closest star to our solar system at 4.2 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 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 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