Origins of Constellations Ancient constellations: Constellation names we use derive from ancient Mesopotamia (modern day Iraq) Others were added by the Babylonians, Egyptians, and Greeks. “Modern” constellations 40 more were added by 1600s IAU officially defined 88 constellation boundaries in 1928 EVERY culture around the world has their own constellations Asterisms – named groups of stars that are NOT constellations ex: Big Dipper, Great Square Stars that make up constellations are all different distances from our Earth and Sun.
Star Names The "common" names derive from ancient Arabic, and often have meanings EX: Rigel = leg Betelgeuse = armpit of the giant Deneb = tail Altair = bird
Star Names in 1603, the first "modern" naming system was developed by Johann Bayer, using: the Greek alphabet for the brightness of the star the Latin name of the constellation EX: the brightest star in Orion (Betelguese) is also called a Orionis, the 2nd brightest, is called b Orionis one problem with this system is that some stars vary their brightness - Betelgeuse is NOT always brighter than Rigel! There are over 10 different systems that are/have been used for naming stars
The Many Names of Betelgeuse Alpha Orionis 58 Ori HR 2061 HD 39801 SAO 113271 BD+07 1055 HIP 27989 H 6 ADS4506 WDS 05552+0724 TYC 0129-1873-1
Star Brightnesses - the Magnitude Scale Introduced by Hipparchos (160 - 127 BC) Divided the stars into 6 classes brightest stars were 1st magnitude faintest stars were 6th magnitude (unaided eye) larger the magnitude, the fainter the star! Today it is similar, but more mathematical, logarithmic scale 1st magnitude stars are 100 x brighter than 6th magnitude stars 1 magnitude difference = 2.512 x difference in brightness, so A 1st mag star is 2.5 times brighter than a 2nd mag star, and a 1st mag star is 2.5 times 2.5 times brighter than a 3rd mag star
Star Brightnesses - the Magnitude Scale formalizing the mathematics has produced stars with negative magnitudes (Sirius = -1.42) Magnitude scale has been extended to all astronomical objects
Scientific Models way of representing an object, process, or behavior, to make it more understandable Can be: a physical object (globe) a mathematical formula (F = ma) a conceptual idea Doesn’t have to be correct in order to be useful!
Celestial Sphere Model of Universe Earth-center (geocentric) Stars orbit the earth, attached to a huge sphere Pivots above the N and S poles (NCP & SCP) Half way between, above Earth’s equator is the: Celestial Equator divides the northern sky from the southern sky Passes through East and West points Fully developed by about 200 B.C. Believed to be true until around 1550
Rotation vs Revolution Rotation is: Spinning Earth rotates once every: Revolution Orbiting Earth revolves around the Sun once every:
Sun’s Apparent Motion Sun appears to slowly move Eastward along the ecliptic Over one year, it traces out the ecliptic Plane of Earth’s orbit around the Sun Plane of the solar system
Sun’s Apparent Motion Planets also move Eastward along the ecliptic 12 constellations the ecliptic passes through are the zodiac