Origins of Constellations Ancient constellations Constellation names we

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 1600 s • 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 2 nd 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 ADS 4506 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 1 st magnitude – faintest stars were 6 th magnitude (unaided eye) – larger the magnitude, the fainter the star! • Today it is similar, but more mathematical, logarithmic scale – 1 st magnitude stars are 100 x brighter than 6 th magnitude stars – 1 magnitude difference = 2. 512 x difference in brightness, so – A 1 st mag star is 2. 5 times brighter than a 2 nd mag star, and a 1 st mag star is 2. 5 times brighter than a 3 rd 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