1. Locating Objects in Space

2. Constellations 88 constellations in the night sky
28 northern hemisphere, 12 zodiac, 48 southern hemisphere
Used as navigational guide
Each culture has different names, all recognize the same star groupings
Greek letters are used for identifying the brightest stars in constellations
 Alpha  Beta γ Gamma
Bright Dim

6. Reference Points Zenith – point directly above you in the sky
Celestial Sphere – imaginary sphere surrounding the earth on which the stars are located (Stars only appear to be on celestial sphere)
Celestial Poles – extensions of earth’s geographic poles (North Pole – Polaris…the pole star)
Celestial Equator – extension of Earth’s equator
Ecliptic – apparent path of the sun on the celestial sphere

8. Celestial Coordinates: “directions” to help you find objects in the night sky
Declination: degrees North & South of the celestial equator
*like latitude on Earth or altitude above the horizon
Right Ascension: hours, minutes, & seconds east of the vernal equinox (where the celestial equator and ecliptic cross one another)
*like longitude on Earth

9. Zodiac Constellations: 12 constellations through which the sun passes in a years time (found along ecliptic)
Circumpolar Constellations: constellations that can be seen throughout the year at your latitude (“circle the pole”)

12. How do we locate the planets?
All planets orbit within a few degrees of the ecliptic
Superior Planets (Jupiter – Neptune) can generally be seen any night, except when on the opposite side of the sun
Generally move eastward in celestial sphere from night to night
Retrograde Motion – occasional westward motion due to Earth “overtaking” the planet in its orbit

13. Planets – December 2008

14. Visible in the morning sky
Planets – April 2009
Visible in the morning sky

15. Properties of Stars
Can be measured in terms of diameter, mass, brightness, energy output (power), surface temperature, & composition
Diameters: range from 0.1 times the Sun’s diameter to 100 times larger
Mass: ranges from 0.01 to 20 or more times the Sun’s mass…some are 50 – 100 times the Sun’s mass but are extremely rare

16. Apparent Magnitude: how bright a star appears to be.
Ranges from 1st – 6th magnitude, 1st is 100 times brighter than 6th
Difference of 1 magnitude corresponds to a factor of in brightness
Does not take into account the distance of the star

17. Absolute Magnitude: the brightness of an object if they were all lined up at the same distance away
Changes the scale a bit since distance is taken into account
Sun is brighter than Sirius on apparent magnitude scale, but less bright on absolute magnitude scale
Determine distance using parallax – apparent shift in position of star caused by motion of observer

18. Luminosity: total amount of energy given off by a star
Depends on distance and magnitude
Extremely wide range (millions of times greater than the sun to thousands of times less than the sun)
Composition:
Hydrogen and Helium make up 98% of all stars
1 – 2 % Oxygen, Carbon, Nitrogen, Calcium

19. (Oh Boy An F Grade Kills Me!)
Temperature: determined by star’s spectrum (hotter the star, greater the ultraviolet and less the infrared rays)
Spectral classes: O, B, A, F, G, K, M
(Oh Boy An F Grade Kills Me!)
O is the hottest and M is the coolest
Each class is divided into 10 subdivisions labeled
0 to 9 (a B1 star is hotter than a B8 star)

21. H-R Diagrams
Hertzsprung – Russell Diagrams compare luminosity and temperature
Main sequence stars (80-90%) trend from faint, cool stars in lower right to hot, bright stars in upper left
Giants and Supergiants - located above main sequence
White dwarfs – stars located below the main sequence
Largest stars in the upper right and smallest stars in the lower left
Five Luminosity Categories: I. supergiants, II. bright giants, III. giants, IV. subgiants, V. main sequence
Our Sun is a G2V star

23. Stellar Evolution
Mass: determines type of length of the life of a star
The more massive a star, the shorter its life will be
Stages of Life:
Nebulas: begin as huge clouds of gas and dust
Protostar: gravity causes nebula to contract or collapse on itself forming a disk shape
During early stages, not yet hot enough for nuclear fusion & emits no visible light
Core temperatures finally reach 8-10 million Kelvins, high enough for nuclear fusion & star is “born”
Hydrogen is converting to Helium

24. A - North American Nebula - emission nebula B - Jewel Box open cluster
C - Globular Cluster 47 Tucanae
D - Cygnus Loop - supernova remnant

25. Three main evolutionary paths based on initial mass of star
1st Path: (0.1 to 8 solar masses)
Main Sequence – lifetime determined by amt of fuel available & rate of consumption
Greater the star’s mass the faster it burns up its fuel & the shorter the time it will be a main sequence star
Some stars spend 90% of life as main sequence star

26. Planetary nebula: expanding shell of gases expelled into space
Red Giant: star is running out of hydrogen fuel, cools, gets bigger and becomes more luminous
Helium flash occurs at red giant stage that many only last a few minutes/seconds, star shrinks briefly than resumes red giant status
Planetary nebula: expanding shell of gases expelled into space
Gases keep expanding until they dissipate in interstellar space
Core star left, but center becomes white dwarf.
White dwarf: small star (about size of Earth), super dense, very high temperatures.
Cools over billions of years to become black dwarf
Some can become supernova

28. 2nd Path: stars 8 – 25 solar masses
Main sequence: much shorter than for smaller stars, more fuel but consumed at a faster rate
Red Supergiant: larger and more luminous
Supernova: star that blows off its outer shell into interstellar space, luminosity soars & may outshine entire galaxy
Estimates show 1 supernova per galaxy every years…we have never observed a supernova in our galaxy with a telescope
Neutron Star: small (about size of large city), compact stars
Can give rise to pulsars – rapidly rotating stars that give off pulses of energy

30. 3rd Path: stars 25 – 130 solar masses
Main Sequence: consume fuel at a much faster rate than any of the previous stars
Red Supergiant: similar to red supergiants for path 2
Supernova: referred to as Type II supernova for paths 2 and 3
Black Hole: density so high that escape velocity of star becomes equal to the speed of light, so even light cannot escape