1. C.17 The Milky Way
When we try to pick out anything by itself, we find that it is tied to everything else in the universe.
John Muir ( )

2. For comparison of the following slides, the distance from the Sun to Neptune is 8.44 light hours or light years.

3. For comparison the Milky way is 100,000 light years in diameter.

4. Nebulas A glowing cloud of gas and dust is called a nebula
There are 3 different kinds. Emmission, Dark and Reflection.
Emission nebula - a cloud of glowing gas
The Great Nebula in Orion is an Emission nebula.
It is 1,344 light years away and 24 light years across.
Orion. It is one of the brightest nebulae, and is visible to the naked eye in the night sky. M42 is located at a distance of 1,344 ± 20 light years[3][6] and is the closest region of massive star formation to Earth. The M42 nebula is estimated to be 24 light years across. It has a mass of about 2000 times the mass of the Sun.

5. The Trapezium. A group of 4 stars in the middle of the Orion Nebula
The Trapezium. A group of 4 stars in the middle of the Orion Nebula. These are young, hot, blue stars.

6. NGC 3576 (also known as The Statue of Liberty Nebula and ESO 129-EN5) is a bright emission nebula about 100 light-years across, located some 9000 light-years away in the Sagittarius arm of our Milky Way in the constellation Carina.
This giant nebula of glowing gas is an H II region where stars are currently forming at a high rate. H II (H-two) regions are where stars are born from condensing clouds of hydrogen gas (they are named for the large amounts of ionized atomic hydrogen they contain.) These regions are characterized by hot, young, massive stars which emit large amounts of ultraviolet light and ionize the nebula.

7. Dark Nebulas
In a dark nebula dust and gas that is not glowing is outlined by glowing gases and stars behind it.
The Horsehead Nebula, which is close to the Great Nebula in Orion, is an example of a dark Nebula
It is 13 light years across and 1500 light years away

9. The Snake Nebula in the constellation Ophiuchus

10. Barnard Dark Nebula in Ophiuchus

11. Elephant’s trunk Nebula
Elephant’s trunk Nebula. The Elephant's Trunk nebula is a concentration of interstellar gas and dust in the star cluster IC 1396 – an ionized gas region located in the constellation Cepheus about 2,400 light years away from Earth. The Elephant's Trunk nebula is now thought to be a site of star formation, containing several very young (less than 100,000 yr) stars that were discovered in infrared images in 2003.

12. The Boogie Man Nebula (also known as Lynds’ Dark Nebula (LDN) 1622) is a dark molecular cloud of less than 10 light-years across that lies only 500 light-years away in the constellation of Orion, close on the sky to Barnard’s Loop and just north of Orion’s belt, near the plane of our Milky Way Galaxy.
The Boogie Man Nebula appears against a faint background of glowing hydrogen gas. The interstellar dust of this dark nebula is so thick that it obscures light from nearby stars or other nebulas.
This nebula demonstrates the evolution of stars. Star formation results from the collapse of giant clouds of molecular gas and dust. The stars eventually emerge into visibility with their blue light scattering and reflecting off dust particles present in the gas.

13. N44 superbubble - Larg Magellanic cloud
In the area of NGC1929 in the LMC is found the complex nebula seen above.  Known as the N44 superbubble complex, this turbulent emission nebula is dominated by a vast bubble about 325 by 250 light-years across. The bubble's interior is formed either by massive winds produced by a cluster of  stars combined with the remnant shell of old supernovae. If you look closely along the left of the nebula you can discern the presence of a second bubble.  As superbubbles expand and age their surface brightness diminishes.  Finally it is thought that superbubbles can trigger new star formation in areas of the shells where gases condense.

14. Reflection Nebula
Reflecting Nebulas occur when clouds of gas and dust reflect the light of stars that are within.
The Pleiades, Seven sisters, or Subaru is an example of a Reflection Nebula.
It is about 12 light years in diameter and 440 light years away.

16. The pillars were composed of cool molecular hydrogen and dust that were being eroded away by photoevaporation from the ultraviolet light of relatively close and hot stars. The leftmost pillar was about four light years in length.[3] The finger-like protrusions at the top of the clouds were larger than our solar system, and were made visible by the shadows of Evaporating Gaseous Globules (EGGs), which shielded the gas behind them from intense UV flux.[4] EGGs are themselves incubators of new stars

17. North American and Pelican Nebulas
the nebula complex would be about 1800 light years distance, and its absolute size (6° apparent diameter on the sky) would be 100 light years. The North America Nebula (NGC 7000 or Caldwell 20) is an emission nebula in the constellation Cygnus, close to Deneb (the tail of the swan and its brightest star). The North America Nebula and the nearby Pelican Nebula, (IC 5070) are in fact parts of the same interstellar cloud of ionized hydrogen (H II region). Between the Earth and the nebula complex lies a band of interstellar dust that absorbs the light of stars and nebulae behind it, and thereby determines the shape as we see it. The distance of the nebula complex is not precisely known, nor is the star responsible for ionizing the hydrogen so that it emits light. If the star inducing the ionization is Deneb, as some sources say, the nebula complex would be about 1800 light years distance, and its absolute size (6° apparent diameter on the sky) would be 100 light years.

18. Eagle Nebula. The Eagle Nebula is part of a diffuse emission nebula, or H II region, which is catalogued as IC This region of active current star formation is about 7000 light-years distant. The tower of gas that can be seen coming off the nebula is approximately 9.5 light-years or about 90 trillion kilometers high.

19. The Heart and Soul nebulae stretch out nearly 580 light-years across, they are 7500 light years away in the constellation Cassiopeia
The heart nebula IC 1805

20. Cone Nebula
In the constellation Monoceros. The cone's shape comes from a dark absorption nebula consisting of cold molecular hydrogen and dust in front of a faint emission nebula containing hydrogen ionized by S Monocerotis, the brightest star of NGC The faint nebula is approximately seven light-years long (with an apparent length of 10 arcminutes), and is 2,700 light-years away from Earth

21. The Cone Nebula and the Christmas Tree cluster
The Cone Nebula and the Christmas Tree cluster. The cone nebula is 7 light years long and 2,700 l.y. away.
The faint nebula is approximately seven light-years long (with an apparent length of 10 arcminutes), and is 2,700 light-years away from Earth.

22. Lagoon Nebula
The Lagoon Nebula (catalogued as Messier 8 or M8, and as NGC 6523) is a giant interstellar cloud in the constellation Sagittarius. It is classified as an emission nebula and as an H II region. The Lagoon Nebula is estimated to be between 4,000-6,000 light years from the Earth. In the sky of Earth, it spans 90' by 40', translates to an actual dimension of 110 by 50 light years.

23. Center of Lagoon Nebula The light from M8 we see today left about 5000 years ago. Light takes about 50 light years to cross this section of M8.

24. Carina Nebula 2 light years in diameter and 8,000 l.y. away.
The Carina Nebula (also known as the Great Nebula in Carina, the Eta Carina Nebula, or NGC 3372, as well as "Grand Nebula") is a large bright nebula that surrounds several open clusters of stars. Eta Carinae and HD 93129A, two of the most massive and luminous stars in our Milky Way galaxy, are among them. The nebula lies at an estimated distance between 6,500 and 10,000 light years from Earth. It appears in the constellation of Carina, and is located in the Carina–Sagittarius Arm. The nebula contains multiple O-type stars.

25. This craggy fantasy mountaintop enshrouded by wispy clouds looks like a bizarre landscape from Tolkien's "The Lord of the Rings" or a Dr. Seuss book, depending on your imagination. The NASA Hubble Space Telescope image, which is even more dramatic than fiction, captures the chaotic activity atop a three-light-year-tall pillar of gas and dust that is being eaten away by the brilliant light from nearby bright stars. The pillar is also being assaulted from within, as infant stars buried inside it fire off jets of gas that can be seen streaming from towering peaks. Scorching radiation and fast winds (streams of charged particles) from super-hot newborn stars in the nebula are shaping and compressing the pillar, causing new stars to form within it. Streamers of hot ionized gas can be seen flowing off the ridges of the structure, and wispy veils of gas and dust, illuminated by starlight, float around its towering peaks. The denser parts of the pillar are resisting being eroded by radiation much like a towering butte in Utah's Monument Valley withstands erosion by water and wind

26. Eta Carinae, the most energetic star in the nebula, was one of the brightest stars in the sky in the 1830s, but then faded dramatically. The Keyhole Nebula, visible left center, houses several of the most massive stars known and has also changed its appearance. The entire Carina Nebula spans over 300 light years and lies about 7,500 light-years away in the constellation of Carina. Pictured above is the most detailed image of the Carina Nebula ever taken. The controlled color image is a composite of 48 high-resolution frames taken by the Hubble Space Telescope and released to honor its 17th anniversary.

27. Hubble Space Telescope image showing Eta Carinae and the bipolar Homunculus Nebula which surrounds the star. The Homunculus was created in an eruption of Eta Carinae, the light from which reached Earth in Eta Carinae itself appears as the white patch near the center of the image, where the two lobes of the Homunculus touch

28. Trifid Nebula 65 l.y. away and 11 l.y. across in Saggitarius

29. This Hubble Space Telescope image of the Trifid Nebula reveals a stellar nursery being torn apart by radiation from a nearby, massive star. The picture also provides a peek at embryonic stars forming within an ill-fated cloud of dust and gas, which is destined to be eaten away by the glare from the massive neighbor

30. Rosette Nebula
The Rosette Nebula (also known as Caldwell 49) is a large, circular H II region located near one end of a giant molecular cloud in the Monoceros region of the Milky Way Galaxy. The open cluster NGC 2244 (Caldwell 50) is closely associated with the nebulosity, the stars of the cluster having been formed from the nebula's matter.

32. Coal Sack
The Coalsack Dark Nebula (or simply the Coalsack) is the most prominent dark nebula in the skies, easily visible to the naked eye as a dark patch silhouetted against the southern Milky Way. It was known pre-historically in the Southern Hemisphere and was observed by Vicente Yáñez Pinzón in The Coalsack is located at a distance of approximately 600 light years away from Earth, in the Crux constellation.

33. Milky Way Structure
Harlow Shapley deduced the structure of the Milky Way in 1920.
He noticed that globular clusters were all in the same general area of the sky.
In plotting their distances from the earth he noted that they form a spherical halo above and below the galactic plane.
This halo was centered around a point thousands of light years away.
Shapley realized that this point must be the galactic center.

34. Hypothetical Structure
Based on observations people first felt that the Milky Way was a spiral galaxy and that we are located on the Orion spur.
Our galaxy is about 100,000 light years across. We are about 33,000 light years from the nuclear bulge.
Our sun and spiral arm rotates around the nuclear bulge in a clockwise direction.
Hypothetical Structure

35. Milky Way Structure cont.
The use of different types of telescopes has helped us get a better idea of the shape of our galaxy.
This is an infrared photo of our galactic disk and bulge taken by the COBE satellite.

39. Globular clusters - a halo of these exist around the Galactic core

40. Modern Galaxy maps
The first good map of the Milky Way was made by Oort, Kerr and Westerhout (1958)
They mapped neutral hydrogen in the plane of the galaxy.
1976 Yvonne and Yvon Georgelin mapped all of the bright nebula and showed they existed in the spiral arms.

41. Milky Way Map cont.
In the 1990’s researchers first found evidence that our galaxy is a barred spiral galaxy.
The early maps based on these observations looked like this one.

42. Studying the center
Observations of radio waves and infrared radiation help us penetrate the thick dust and light that hides the center.
A very bright radio wave source is indicated in the center of our galaxy ( as bright as 80 million suns)
In the center there is evidence of an extremely narrow radio source 10 A.U. across. This could be a massive black hole.
It is called Sagittarius A
This slide is a radio image of the central disk taken from the Very Large Array, near Soccoro, New Mexico.

43. Very large array, Soccoro, New Mexico

45. Chandra X-ray picture of bulge

46. The Chandra X-ray Observatory is a satellite launched by NASA on July 23, It was named in honor of Indian-American physicist Subrahmanyan Chandrasekhar who is known for determining the maximum mass for white dwarfs. "Chandra" also means "moon" or "luminous" in Sanskrit.

47. Chandra is sensitive to X-ray sources 100 times fainter than any previous X-ray telescope. The Earth's atmosphere absorbs the majority of X-rays. This requires a space-based telescope to make these observations.

48. Spitzer Space Telescope
Chandra Observatory is the 3rd of NASA's 4 great Observatories. The first was Hubble Space Telescope; second the Compton Gamma Ray Observatory, launched in 1991; and last is the Spitzer Space Telescope.
Compton Gamma Ray Observatory
Spitzer Space Telescope

49. The Spitzer Space Telescope is an infrared space observatory launched in The planned mission period was to be 2.5 years with an expectation that the mission could extend to five more years until the onboard liquid helium supply was exhausted. This occurred on 15 May 2009.

50. In keeping with NASA tradition, the telescope was renamed after successful demonstration of operation, on December 18, Unlike most telescopes which are named after famous deceased astronomers by a board of scientists, the name for SIRTF was obtained from a contest open to the general public. The contest led to the scope being named in honor of Lyman Spitzer, one of the 20th century's great scientists. Spitzer wrote a 1946 report for RAND describing the advantages of an extra-terrestrial observatory and how it could be realized with available (or upcoming) technology.

51. The Compton Gamma Ray Observatory was the second of the NASA "Great Observatories" to be launched to space, following the Hubble Space Telescope. It was named after Dr. Arthur Holly Compton (Washington University in St. Louis), Nobel prize winner, for work involved with gamma ray physics. The observatory was launched on the Space Shuttle Atlantis, on 5 April 1991 and operated until its deorbit on 4 June It was deployed in low earth orbit at 450 km (280 miles) to avoid the Van Allen radiation belt. It was the heaviest astrophysical payload ever flown at that time at 17,000 kilograms (37,000 lb)

52. Bulge x-ray info
The previous slide was a mosaic of images taken by the x-ray satellite Chandra.
It showed several large sources of x-rays which are believed to by neutron stars and a strong candidate for a black hole in the central bright spot of the slide.

53. Spiral Shape People deduce that the galaxy has a spiral shape.
Open clusters always appear in spiral arms.
Spiral arms are where young stars are found.
Emission nebula are found in the spiral arms.
Plotted distances to these regions trace out parts of 3 spiral arms.

54. Intersteller medium
The IRAS satellite, pictured here, has discovered vast clouds of Hydrogen gas between and connecting with the spiral arms.
This satellite takes infrared pictures and can detect matter that is barely above absolute zero.

55. The Infrared Astronomical Satellite (IRAS) was the first-ever space-based observatory to perform a survey of the entire sky at infrared wavelengths.
Launched on January 25, 1983, its mission lasted ten months.
The telescope was a joint project of the United States (NASA), the Netherlands (NIVR), and the United Kingdom (SERC).
IRAS's life was limited by its cooling system.
The on-board supply of fluid helium was depleted after 10 months on November 22, 1983.
This caused the telescope temperature to rise, preventing further observations
IRAS

56. Molecular clouds
Vast clouds of gas and dust exist in and around our galaxy.
These clouds like the Orion cloud pictured here, form the building blocks of stars in our galaxy.

58. The Local group
Our galaxy is the 2nd largest of a collection of galaxies called the local group.
Included in this group are the Large and Small Magellenic clouds, Sculptor and Fornax dwarf galaxies, Leo I and Leo II dwarf galaxies, M33, elliptical galaxy Maffei I and Maffei II and of course M31 the giant Andromeda galaxy.

59. M33 – Triangulum galaxy or pinwheel galaxy 3rd largest of the local group, 3,000.000 l.y. away

60. Magellanic Stream
A large cloud of hydrogen gas surrounds our galaxy and includes the Large and Small Magellanic clouds.
This cloud orbits our galaxy as do the Large and Small Magellanic clouds.

61. M33 Pinwheel Galaxy

62. Large Magellanic cloud The brightest galaxy visible from Earth
Large Magellanic cloud The brightest galaxy visible from Earth. It is an irregular small galaxy. It is 160,000 l.y. away. It is the 4th largest galaxy in the local group. The Tarantula nebula is the largest nebula known.
1/10th as big as the Milky Way.

63. Large Magellanic Cloud

64. Tarantula Nebula
The Tarantula Nebula in the Large Magellanic Cloud is largest Nebula known.
With a diameter of 800 l.y. and a mass of 300,000 suns, it dominates the Large Magellanic cloud
If it were as close to us as the Great Nebula in Orion it would be as large and as bright as the moon.

65. Hubble Mosiac of Tarantula Nebula (30 Doradus, Central Region The image of 30 Doradus is a mosiac of 5 fields-of-view of one of the Hubble Space Telescope's instruments, the Wide Field Planetary Camera-2. Three filters were used creating an image that shows the stars according to their real colors.

67. Small Magellanic Cloud. 200,000 l. y. away
Small Magellanic Cloud. 200,000 l.y. away. May have been warped in shape by the Milky Way. 7,000 l.y. across and contains several million stars.

68. The Large Magellanic cloud

69. A view of the Large and Small Magellanic clouds from the southern skies

70. M31 Andromeda Galaxy, 2. 2 million l. y
M31 Andromeda Galaxy, 2.2 million l.y. away rotating counterclockwise and formed at the same time as ours.

71. Scultpor dwarf galaxy About 8,000 l.y. in diameter.
Has about 2 million stars like our sun.
Very loosely organized galaxy.
It orbits the Milky Way along with a number of other dwarf galaxies.

72. Fornax dwarf galaxy

73. Sextans dwarf galaxy

74. Leo I dwarf galaxy

75. Sagittarius dwarf galaxy
The closest galaxy to the Milky Way is not the Large and Small Magellanic clouds.
Named the " Sagittarius Dwarf ", this small galaxy was discovered in 1994.
The reason the Sagittarius Dwarf hadn't been discovered earlier is because it is dim, it is spread out over the sky, and there are so many Milky Way stars in front of it.
The distance to the Sagittarius Dwarf was measured to be about one third of the distance to the LMC.
Astronomers believe that this galaxy is slowly being torn apart by the gravitational forces of our Galaxy.
Sagittarius dwarf galaxy