1. The study of the universe beyond the Earth’s atmosphere
Astronomy
The study of the universe beyond the Earth’s atmosphere

2. Theories of the Universe
Geocentric Theory: this theory, put forward by the ancient Egyptian astronomer Ptolemy, states that the Earth is the center of the universe.
Heliocentric Theory: this theory, put forward by the Polish scientist Copernicus, states that the Sun is the center of the universe.

3. Ptolemy and Geocentric Theory

5. Copernicus and Heliocentric Theory

6. What is the Solar System?
The Solar System is: the Sun, the eight planets and their natural satellites, the asteroids, the comets and the meteoroids.

7. What is a planet?
Planet = a massive collection of matter that revolves around a celestial body, or star.

8. The Eight Planets Mercury Venus Earth Mars Jupiter Saturn Uranus
Neptune
Pluto = dwarf

9. Planets are divided into two categories
Terrestrial Planets are “land-based” planets that are solid, dense, “hot” and have few moons:
Mercury
Venus
Earth
Mars
Pluto
Gaseous Giants are “gaseous” planets that are big, low density, “cold” and have many moons:
Jupiter
Saturn
Uranus
Neptune

10. Mercury Closest to the sun Thin atmosphere
Day is 450 oC hot, night is -170 oC cold
Has many craters
Day is twice as long as its year

11. Venus 2nd planet from the Sun Hot 470 oC
Has an atmosphere of poison gas that causes sulfuric acid rain
Has storms
Day is longer than the year

12. Earth 3rd planet from the Sun Only known planet with liquid water
Average temperature of ~ 12 oC
Has one moon
Has ice caps on the poles

13. Mars
4th from the sun
Called the “Red Planet” due to large amounts of iron oxide (rust) on surface
Also called the sister to earth
Rocky composition
Temperature range is -20 oC to -140 oC
Has polar ice caps.
2 moons, Deimos and Phobos

14. Jupiter 5th from the sun Larger than all the other planets combined
High gravity makes the gas into a liquid and therefore there are “oceans”
Great Red Spot is a storm on the surface of the planet that is ~ 3 times the size of earth
Jupiter has 63 moons.

15. Saturn 6th from the sun 2nd largest planet in solar system
Has a low density, it would float in water
Rings are made of particles of ice, dust and rock
Saturn has 60 moons.

16. Uranus 7th from the sun Planets axis is tilted on it’s side
Green/blue color is from methane gas, hydrogen and helium composition
Uranus has thin rings and 27 moons.

17. Neptune 8th from the sun Blue color is from methane gas composition
Great Dark Spot is a storm on the surface
Neptune has 13 moons, moon Triton is mostly nitrogen = possible atmosphere.

18. Pluto 9th from the Sun Cold Rocky composition
Pluto is considered a dwarf planet
Pluto has one moon, Charon, almost as large as Pluto itself
Pluto and Charon together orbit the Sun in an unusual path

19. Other Dwarf Planets
Ceres
Haumea
Makemake
Eris

20. Planetary Paths - Orbits
Planets travel around the sun in a path called an orbit.
Planetary orbits are elliptical in shape.
Elliptical orbits are compared based on how eccentric, or out of round, they are.
A perfect circle has an eccentricity of 0 (no out of round shape) and a line has an eccentricity of 1 (maximum out of round)

21. Planetary Orbits

22. Orbits
All the planets revolve around the sun in a counter-clockwise motion.
The planets are held in place by the gravitational force of the Sun.
Planets move fastest through their orbit when they are closest to the sun.

23. What is our Sun?
Our Sun is an average star of yellow-orange classification.

24. Layers of the Sun The sun is composed of several layers. Core
Radiative zone
Convective zone
Corona
Photosphere
Chromosphere

26. The Core
The core of the Sun is the place where fusion of atoms is taking place.
Fusion generates temperatures of 10,000,000 oC
Our sun is fusing hydrogen atoms into helium

27. The Corona
Corona = the outer layer of the sun. This is the gradual boundary between the sun and space. This is what we see during an eclipse.

28. The Photosphere
Photosphere = the layer of the sun that is incredibly bright and the source of much of the light we see on earth.

29. The Chromosphere
Chromosphere = is an active layer of the sun that is where the magnificent displays of prominence and flares take place.

30. Prominence / Solar Flares
Prominence / Flares are bright spots on the sun formed as gas particles shoot outward from the sun.
These affect the magnetic fields on earth (radio, television, communications).
These also cause the Northern Lights or “Aurora Borealis”.

31. Aurora Borealis – “Northern Lights”

32. Northern Lights

36. Sun spots
Sun spot = a dark, cooler spot on the surface of the sun.

37. What are Stars?
Star = a hot, glowing sphere of gas that produces energy by fusion (of hydrogen molecules).
Some stars produce more energy therefore they are hotter.

38. How Do Stars Form?
Nebula = a cloud of dust and gas where stars are born.
Here gravity pulls particles together and fusion starts at 10,000,000 oC and a star is born.

39. The Horse Head Nebula

40. More Horse Head Nebula Shots

42. How Are Stars Classified?
Stars are classified by:
Temperature
Color
Brightness

43. Stars are Classified by Temperature and Color.
HOT COLD
BLUE
WHITE
YELLOW
ORANGE
RED
BROWN

44. What is a Main Sequence Star?

45. Stars are Classified by Brightness
Actual brightness is how bright a star really is.
Actual brightness does not change, it is an absolute value.
Example: a 40 watt light bulb is actually converting 40 watts of energy into light.
Apparent brightness is how bright a star looks from earth.
Apparent brightness changes depending on distance from earth and viewing conditions (atmosphere).
Example: a 40 watt light bulb 10 feet away appears brighter than a 40 watt bulb 100 feet away.

46. …And After Stars are Born?

47. Life Cycle of a Star

49. What is a Supernova?
Supernova is when the core of a star collapses and the outer portion explodes.
This is the “death of a star”.
What remains when a star dies out depends on the mass of the star.
The most massive stars collapse into black holes.

51. What is a Black Hole?
Black Hole = the most dense thing known to exist in the universe. The gravity of a black hole is so great that even light can not escape the pull of a black hole.

52. The massive density of Black Holes creates a gravitational force that pulls in anything that comes within reach: the reach of this force is called the event horizon.

54. The fate of objects that enter a Black Hole is still uncertain.?

55. Other Objects in the Solar System
Other objects in the solar system include:
Comets
Asteroids
Meteoroids

56. What is a Comet?
A Comet is a large chunk of ice, dust, frozen gas and rock fragments that moves through space.

57. Comets form in an icy cloud, called the Oort Cloud, as the gravity of a passing star pulls material out of the cloud.

58. Comets Have Two Tails The Ion Tail always points away from the sun
The Dust Tail is left behind in the comets path

59. Halley’s Comet

60. Comet - Liner

62. Asteroids Asteroid = a large chunk of rock traveling through space.
Most, not all, are found in the asteroid belt located between Mars and Jupiter.

64. Asteroid approaching Earth

65. Asteroid Impact

66. Meteoroid, Meteor, Meteorite
Meteoroids = small pieces of rock moving through space.
Meteors = small pieces of rock moving through space (a meteoroid) that enters Earth’s atmosphere.
Meteorite = a small piece of rock moving through space that hits the Earth.

69. Perseid Meteor Shower

70. How are Distances Measured in Space?
Astronomical Unit (AU) is the distance from the Earth to the Sun.
1 AU = ~92,000,000 miles
Light Year (LY) is the distance that light travels in one year.
1 LY = ~6 trillion miles

71. Light Year = Distance
1 light-second = AU = 186,322 miles 1 light-minute = AU = mil. miles 1 light-hour = AU = million miles 1 light-day = AU = billion miles 1 light-week = AU = billion miles 1 light-month = AU = billion miles 1 light-year = AU = 5.89 trillion miles

72. Our Planets in Light Years
OBJECT
Light-travel Distance
Mercury
3.22 light-minutes
Venus
6.01 light-minutes
Earth
8.32 light-minutes
Mars
12.7 light-minutes
Jupiter
43.3 light-minutes
Saturn
1.32 light-hours
Uranus
2.66 light-hours
Neptune
4.16 light-hours
Farthest comets
1.58 light-years
Proxima Centauri
4.3 light-years
Orion Nebula
1,500 light-years
Center of Milky Way
26,000 light-years
Andromeda Galaxy
2.36 million light-years

73. What is a Galaxy?
Galaxy = a large group of stars, gas and dust held together by gravity.

74. Three Types of Galaxies
Elliptical Galaxy
Spiral Galaxy
Irregular Galaxy

75. Elliptical Galaxies
Elliptical galaxies = are groups of stars that appear to be shaped like an ellipse (football)

76. Irregular Galaxies
Irregular galaxies = are groups of stars that appear to be together but have no regular shape.

77. Irregular Galaxy

78. Spiral Galaxies
Spiral galaxies = are groups of stars that appear to have a dense concentration of stars in the center and arms that are made of stars and dust.

79. Barred Spiral Galaxy
A “Barred” Spiral galaxy looks similar to a spiral galaxy with a “bar” of stars through the center and the arms extend outward from the ends of the “bar”.

80. Clusters
As stars are grouped into galaxies, galaxies are grouped into clusters.
Our cluster is called the “Local Group”

81. So Where in the Universe Are We?
The astronomical address for Earth would be:
Earth is the 3rd planet in the solar system of the star called the Sun, which is in the Milky Way Galaxy, of the Local Group of galaxies in the Universe.