Finding Your Way Around the Night Sky

1. Finding Your Way Around the Night Sky Constellations & The Celestial Sphere Every night there are an abundance of interesting objects to look at in the sky Whether you are an amateur astronomer or a professional, you have to know how to find objects from one night to the next

2. Relative Positions - The Constellations • Constellations are simply groups of stars in the sky that appear to form a pattern • Ancient cultures recognized these patterns from season to season • Many constellations have various names from different cultures • The Big Dipper is also known as: • The Wagon or Plough (Western Europe) • The Great Bear (Greek) • The Leg of an Ox (Egyptian) • A Stag (Siberian) • A Funeral Procession (Native American)

3. Orion - Visible in Winter Betelgeuse Rigel

4. Constellations • Constellations serve many purposes • They mark the seasons • Orion in winter, the Summer Triangle in summer • They serve as relative landmarks for finding stars • Analogy: Which is easier? • Joe's house is in Atlanta • Joe's house right next to the Big Chicken in Marietta • Same applies to constellations • Betelgeuse is that red star ... right there (points) • Betelgeuse is the star that makes Orion's right shoulder • They make for good storytelling!

5. Constellations • There are a total of 88 constellations in the sky (most of them relatively unknown) • The twelve signs of the Zodiac are important constellations because they lie in the path of the Sun through the sky (more on this in a sec) • The brightest stars in the sky are given names based on their constellation • The brightest star in a constellation is (usually) called Alpha _____, the second brightest Beta ______, and so on • For example, Betelgeuse is also known as Alpha Orionis, Rigel is also known as Beta Orionis • Remember Alpha Centauri, the nearest star system? It is the brightest star in the constellation Centauris

6. Constellations and The Celestial Sphere • Always remember that how we see the stars on the sky has nothing to do with how they are grouped in space • We have no depth perception when looking at the sky Stars in a constellation that appear to be right next to each other on the sky can actually be 100's or even 1,000's of light years away from each other.

7. The Celestial Sphere • The Celestial Sphere is a simplistic way of thinking about the stars in the sky • Looking up at the stars over the course of a night, it appears simply as a bunch of fixed points of light, moving uniformly across the sky • One can think of this as the Earth being in the middle of a huge ball or sphere with lots of little lights painted on the inside • As the sphere spins, we see the stars move across the sky

8. Reality Check • ALWAYS REMEMBER: it is the Earth's rotation that makes the stars, Sun, Moon, and planets move from east to west in the sky • ALWAYS REMEMBER: each point of light is actually a huge star, all of which are at varying distances from us • The Celestial Sphere is just a very handy way of thinking about the sky and is very useful for finding a specific object in the sky

9. Earth Coordinates Review • Lines of longitude are measured east-west around the globe relative to the prime meridian (Greenwich, England) • 0-180o east or west of the prime meridian • Lines of latitude are measured north-south on the globe relative to the equator • 0-90o north or south of the equator • For example • Atlanta is at: • 84o 23' 16.8" W • 33o 44' 56.4" S

10. Celestial Coordinates • Right ascension (RA) measures east-west on the celestial sphere • Measured in hours, minutes, seconds since one rotation of the celestial sphere is equal to one sidereal day • Remember, the four minute difference between sidereal and solar day will cause stars to not appear at the same exact time and place every night • Declination (DEC) measures north-south of the celestial equator • Measured in degrees, minutes, seconds like latitude • For example, Betelgeuse is at: • RA: 05h 55m 10.3s • DEC: 07o 24' 25.4" RA: 00h 00m 00s to 23h 59m 59s DEC: +90o (north) to -90o (south)

11. The Ecliptic • Because of the tilt of the Earth's rotation axis, the path of the Sun is tilted relative to the celestial equator • The path that the Sun takes through the sky is called the ecliptic • All of the planets (except for Pluto) also follow the ecliptic through the sky

12. Solstices & Equinoxes • There are four special positions along the ecliptic • The summer solstice is when the sun is highest in the sky for the northern hemisphere • The winter solstice happens when the sun is lowest in the sky for the northern hemisphere • The vernal (spring) and autumnal (fall) equinox occur when the sun is crossing the celestial equator

13. What's Your Sign? - The Zodiac • The ecliptic (and therefore the Sun) passes through the twelve signs of the Zodiac • Your birth sign roughly corresponds to the when the Sun is located in your constellation • Notice you cannot see your sign when it is your birth month, since the Sun outshines everything else • This is about all astrology and astronomy have in common, no matter what my mom thinks

14. Observing the Heavens • At any given time, half of the celestial sphere is visible to you • The point directly overhead in the sky is called the zenith • The edge of the visible sky (where the sky meets the ground) is called the horizon • An object's altitude is the vertical angle between the horizon and the object • The zenith distance is the angle between the zenith and the object • Note: 90o - altitude = zenith distance

15. Observing the Heavens • All objects in the sky (the Sun, the Moon, the planets, the star, everything) RISE IN THE EAST and SET IN THE WEST • Not all objects stay in the sky as long as others, due to the tilt of the Earth's axis and your position on the surface • Circumpolar stars are stars near the north celestial pole that neither rise or set

18. On FridayBring a calculatorand a pencil!