A Constellation is… Asterisms …a region of the z These are familiar sky, within official shapes but not official borders set in 1928 constellations by the IAU. • Often recognizable by a pattern or The summer triangle grouping of stars. • Some patterns, like the Winter Triangle, span several constellations. © 2004 Pearson Education Inc., publishing as © 2004 Pearson Education Inc., publishing as Addison-Wesley Addison-Wesley Cygnus More asterisms “a real constellation” z The big dipper z Actually part of Ursa Major Image from: z The Big Bear http://www.physics.csbsju.edu/astro/constellations/ursa_major_l.html z Or Big Raccoon? © 2004 Pearson Education Inc., publishing as © 2004 Pearson Education Inc., publishing as Addison-Wesley Addison-Wesley Lyra—another real constellation Prominent Constellations -Sagittarius. © 2004 Pearson Education Inc., publishing as © 2004 Pearson Education Inc., publishing as Addison-Wesley Addison-Wesley 1 Scorpius Orion z Betelguese z Orion Nebula © 2004 Pearson Education Inc., publishing as © 2004 Pearson Education Inc., publishing as Addison-Wesley Addison-Wesley z Betelguese Not what it appears! Orion Nebula Radius of Earths orbit about sun! Planetary systems forming © 2004 Pearson Education Inc., publishing as © 2004 Pearson Education Inc., publishing as within! Addison-Wesley Addison-Wesley The view from here: The Celestial Sphere Celestial Astrononomy z The sky above looks like z Even though we know the Earth goes a dome…a hemisphere.. around the sun and not vice versa.. z If we imagine the sky z Don’t we? around the entire Earth, z 1/5 adults in USA don’t! we have the celestial sphere. z Its useful to think about a sphere of celestial objects surrounding the Earth z This a 2-dimensional representation of the sky z The signs of the zodiac are the constelltions that are along the sun’s Because it represents path—the ecliptic! our view from Earth, we place the Earth in the © 2004 Pearson Education Inc., publishing as © 2004 Pearson Education Inc., publishing as Addison-Wesley Addison-Wesleycenter of this sphere. 2 The Celestial Sphere Finding the North Celestial Pole North & South celestial poles z Image from younge the points in the sky directly above the Earth’s Observer North and South poles s Merak celestial equator Dubhe the extension of the Earth’s equator onto the celestial sphere ecliptic the annual path of the Sun through the celestial sphere, which is a projection of ecliptic plane Polaris © 2004 Pearson Education Inc., publishing as © 2004 Pearson Education Inc., publishing as Addison-Wesley Addison-Wesley Star Trails in two hemispheres The Daily Motion Southen Hemisphere Northen Hemisphere daily circles --- CCW looking north, CW looking south © 2004 Pearson Education Inc., publishing as How long was the shutter open?© 2004 Pearson EducationWhich Inc., publishing direction as do the stars move? Addison-Wesley Addison-Wesley Images from NASA/APOD 3.