1. Stars and Galaxies

3. Star Observation
Stars are studied by the electromagnetic waves they emit

4. stars produce many kinds of electromagnetic radiation
includes radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays, cosmic rays

6. electromagnetic waves are similar except for wavelength and frequency

12. Optical Telescopes
refractor uses lenses to collect and focus light, but some light lost as it passes throughlenses.

13. reflector telescope uses mirror to collect light, gives brighter images & higher resolution

14. Radio Telescopes
radio waves are not affected by the atmosphere, dust, or light pollution
most space objects emit radio waves

17. Spectroscopes
a star’s visible light has a characteristic spectrum depending on its composition
a spectroscope is used to view the spectrum and identify chemical makeup

18. Absorption spectrum – each element absorbs certain wavelengths of light as it passes through relatively cool gas under low pressure (like the atmosphere of a star). Most stars produce absorption spectra.

19. Emission Spectrum – under certain circumstances, elements can also produce emission spectra, where only certain wavelengths of visible light.

20. Characteristics of Stars:
Color and Temperature
stars vary in color according to temperature
red are cooler than blue
yellow, such as our sun, are in between

21. Characteristics of Stars: Mass
Binary stars orbit a common point – center of mass
More massive stars orbit closer to center of mass
Mass can be calculated of size of orbit is known.

22. Characteristics of Stars: Motion
Stars moving toward us compress light, causing a blue shift. Stars moving away stretch light, causing a red shift.
This is called the Doppler effect

23. Red Shift – can be observed by comparing absorption spectrum of star with one from a stable source.

24. Same principle can be used to detect planets orbiting around distant stars.

25. Characteristics of Stars: Distance
distance to nearer ones can be measured by parallax
the closer the star, the more it appears to change position against its background as earth revolves around Sun
distances measured in light-years
Characteristics of Stars: Distance

26. Characteristics of Stars: Magnitude
Magnitude = brightness
the brighter the star the smaller the magnitude
brightest stars have negative magnitudes

27. Magnitude apparent magnitude is what we see from Earth
absolute magnitude is actual brightness

28. Hertzsprung-Russell Diagram
classifies stars by magnitude and temperature
most common combinations are called main sequence
supergiants, red giants, and white dwarfs are less common,
used to determine star life histories

30. Interstellar Matter Nebulae – clouds of dust & gases Emission nebulae
mostly hydrogen
glow (fluoresce)
absorb UV light of nearby hot star & convert it into visible light.
Reflection nebulae
Dark nebular
Far from bright stars
Appear as starless regions of space

31. Life Cycle of a Star

32. 1. Nebula a glowing cloud of dust or gas in space
often the remains of an exploded star (supernova)
birthplace of new stars

33. 2. Protostar clump of matter gathers Contracts under gravity
Friction of atoms/molecules generates heat
Emits long wavelength infrared and even red light
Protostar core heats more intensely than outer layers
2. Protostar

34. 3. Fusion building of heavier atomic nuclei from lighter ones
With enough gravitational pressure, nuclei of atoms forced together & fuse
4 H atoms form 1 He atom, some matter converted into energy
3. Fusion

35. 4. Main Sequence 90% of star’s life
Outward gas pressure of fusion balances inward pressure of gravity.
Hydrogen  Helium

36. 5. Red Giant Betelgeuse medium-mass star H fuel runs out
core has no fusion, no outward pressure
core collapses, reignites fusion of helium into carbon
star expands into a large, cool star in final stage of life.
5. Red Giant
Betelgeuse

37. 6. White Dwarf collapsed remains of small to medium-mass star
Earth-sized, but very dense
surrounded by planetary nebula, remains of outer layer of red giant

38. 7. The End of a High-Mass Star
Burns through fuel fast
Swells into supergiant
Collapses rapidly
Shock wave causes Type II supernova explosion
Enormous energy released
Elements heavier than iron formed
Neutron stars or black holes are left behind.

39. Neutron Star
very dense collapsed star after explosion combines protons and electrons into neutrons
1 tsp would weigh more than all cars in US

40. Black Hole caused by collapse of very large stars
so dense that even light cannot escape from it

42. Other Deep Sky Objects

43. Special Stars variable stars change brightness
binary stars orbit each other, more common than single stars

44. Nova a star that flares up to great brightness
White dwarf feeding off companion
Could explode as Type IA supernova

45. Supernova
the explosion of a massive star at the end of its life cycle.
releases more energy than all other stars in a galaxy combined

46. Spinning neutron star that gives off flashes of radiation
Pulsar

47. Horsehead Nebula

48. Great Nebula in Orion

49. Galaxies and Star Groups

50. Galaxies
large clusters of matter (stars, gas, dust, planets, asteroids, comets, etc.) held together by gravitational attraction
different types:

51. Spiral Galaxy

53. Elliptical Galaxy

54. Irregular Galaxy

55. Spiral or barred spiral galaxy, 100,000 light years in diameter.
3 spiral arms
200 billion stars
Slowly rotating flattened disk w/ bulge (nucleus) in the center 10,000 light years thick
Rotates once every 250 million years
Surrounded by numerous
star clusters.
We’re in one arm 2/3 from center of galaxy.
The Milky Way

56. Local Group small cluster of about 20 galaxies
ours includes Andromeda Galaxy and Large & Small Magellanic Clouds

57. Go have a look at your galaxy tonight!