Astrophysics Optional Topic E

1. Astrophysics Optional Topic E E1 Introduction to the Universe (2 hours) E2 Stellar Radiation and Stellar Types (4 hours) E3 Stellar Distances (5 hours) E4 Cosmology (4 hours)

2. Notes 63a - Optional Topic E - Astrophysics* ----------------------------------------------------------------------------------E.1.3 Measuring Distances in Space •The Astronomical Unit (AU)- the distance from the earth to the sun...1.5 x 1011 m (150,000,000 km = 93,000,000 miles); only useful for measuring distances inside our solar system; •The Light Year (ly)- the distance light travels in one year: x = v t = (speed of light) (seconds in one year) = (3.0 x 108 ms-1) ( 3.156 x 107 s) = 9.46 x 1015 m t

3. •The Parsec (pc)- the distance light travels in 3.26 years: 1.00 pc = 3.26 ly 1.00 pc = __________________ m

4. F.1.6 Apparent Motion of Stars/Constellations; • The visible objects in the night sky exhibit an apparent motion which has them “rise” in the East and set in the West and trace great circular arcs across the sky. This apparent motion is caused by the rotation of the earth on its axis every 24+ hours.

5. • Closer observation of the location of the visible objects finds that some objects remain fixed in place and others move or “wander” about the sky in other than straight lines or even circular arcs. These “wanderers” are the planets (named by the Greeks) and the follow unusual paths, even moving backward (retrograde motion) when compared to the fixed stars. These motions take days, weeks, months, years, decades and even centuries (depending on the planet) to observe.

6. • As earth revolves around the sun, Sol’s position changes with respect to the fixed stars. It moves from 23.5o north of the celestial equator to 23.5o south of the celestial equator and 360o around the equator each year. When it crosses the celestial equator at the Vernal Equinox (March) and Autumnal Equinox (Sept), there are equal periods of day and night. • The closer stars (< 100 ly) exhibit a proper motion and actually move across the sky in very small increments measured in seconds of arc per year.

7. •Angular “Distances” in space from earth Measured in degrees (o), minutes (‘), and seconds (“) of arc; 1o of arc = 60’ (minutes of arc); 1’ of arc = 60” (seconds of arc); 1o of arc = 3600” (seconds of arc) http://hyperphysics.phy-astr.gsu.edu/Hbase/astro/distance.html

8. For reference...width of full moon as seen from earth... 0.5o of arc = 30’ of arc = 1800” of arc; The closer stars (< 100 ly) exhibit a proper motion and actually move across the sky in very small increments measured in seconds of arc per year;

9. F.1.5 Relative Distances in Space THE UNIVERSE - by powers of ten http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html

10. How far are we from the: Sun? moon? nearest planet? nearest star?

12. Composition of the Universe I. Gas molecules, dust particles, radiation, ions, simple compounds, and samples of all known elements; • Density of interstellar space = 1 x 10-20 kg m-3; • Density of intergalactic space = 1 x 10-25 kg m-3;

13. E.1.1 General Structure of the Solar System • The SUN (Sol) - a red dwarf star (actually “yellow” in appearance) with a surface temp of 6000 K situated in an outer arm of the Milky Way Galaxy; • SOL exerts gravitational control over 8 planets (4 rocky and 4 gaseous), at least 118 “moons,” and uncountable asteroids, meteoroids, and comets that follow elliptical paths around it; - PLANETS...In August 2006, members of the IAU passed a resolution that defined a planet as a celestial body that... 1. is in orbit around the Sun; 2. has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round shape (i.e., it assumes a nearly round shape due to its own gravity;); 3. has cleared the neighborhood around its orbit (i.e., it is the dominant mass in its orbit - Pluto is now considered a dwarf planet);

14. General structure of the solar system http://www.planetsalive.com/

15. General structure of the solar system http://www.planetsalive.com/

18. F.1.1 General Structure of the Solar System;

19. • The Sun (Sol) - a red dwarf star (actually “yellow” in appearance) with a surface temp of 6000K situated in an outer arm of the Milky Way Galaxy; • Sol exerts gravitational control over 8 “major” planets (4 rocky and 4 gaseous), at least 61 “moons,” and uncountable asteroids, meteoroids, and comets; • Solar objects orbit the sun in elliptical orbits with Sol at one focus; some orbits are nearly circular (eg., Mars) while others are highly elliptical (eg., Comet Hyakutake...T = 30,000 years); • Between Mars and Jupiter is the Asteroid Belt - a wide band of pebble-to-asteroid size chunks of rock which may be the remains of a destroyed planet or the “precursors” of a planet which never formed;

20. Introduction to our solar system http://player.discoveryeducation.com/index.cfm?guidAssetId=D7B6623B-0A42-4D6A-BF52-10853D015A8B&blnFromSearch=1&productcode=US

21. II. Nebulae - vast clouds of gas and dust; some are remnants of stellar explosions (super novae) and, with the correct density, others serve as precursors to stars; The Orion Nebula, @ 1500 ly distance and 100 ly diameter, is the closest star-forming cloud of dust and gas to the earth. http://fusedweb.llnl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula.html

22. III. Comets - “small” solid objects made of frozen gases; http://www.nineplanets.org/comets.html Halle-Bop comet 1997 Comet West 1976 -COMETS...large masses of frozen gases; • Solar objects orbit the sun in elliptical orbits with Sol at one focus; some orbits are nearly circular (eg., Mars) while others are highly elliptical (eg., Comet Hyakutake...T = 30,000 years); • Between Mars and Jupiter is the Asteroid Belt - a wide band of pebble-to-mountain sized chunks of rock which may be the remains of a destroyed planet or the “precursors” of a planet which never formed;

23. IV. Asteroids/meteoroids - small bodies usually made of rocky materials; from microscopic to moon-sized; http://www.nineplanets.org/asteroids.html

24. V. Planets/Brown Dwarfs - some planets are “terrestrial” in nature and are made of heavy materials like silicates and heavy metal compounds (eg., earth); some planets consist of gases like H-2 and He and could be the remains of “un-born stars”; Brown Dwarfs (BD’s) are 1% - 10% the mass of the sun and 10-80 times the mass of Jupiter; BD’s are capable of burning deuterium into helium, which can last for several million years, but will then “burn out” and cease fusion; if Jupiter had 10 times its current mass it would have become a BD; if Jupiter had 80 times its mass, it would have become a star; http://chandra.harvard.edu/xray_sources/browndwarf_fg.html

25. VI. Stars - gaseous objects with sustained nuclear fusion taking place in a core that is contained by gravity; Stars may be classified by their surface temperature and/or color or size: Color...............Surface Temp.....Spectral Class Electric blue.......30,000 K.................O Blue...................20,000 K..................B White.................10,000 K..................A Yellow-white........7,000 K..................F Yellow..................6,000 K..................G (Sol, our star) Orange.................4,000 K..................K Red......................3,000 K..................M

26. Stars may be classified by their size: Super Giant........100x -1000x radius of Sol Giant....................10x -100x radius of Sol Dwarf....................Radius of Sol or smaller

27. VII. “Special” Stars A. Black Hole - the remains of a super giant star that gravity has collapsed to a singularity, ie., radius = 0, density = infinite; not even light can escape; http://cosmology.berkeley.edu/Education/BHfaq.html http://scienceblogs.com/startswithabang/upload/2010/07/see_a_quasar_gravitationally_l/hs-2008-04-a-print.jpeg

33. B. Neutron Star - remains of a giant star that gravity has collapsed with such force that the electrons are pushed into the nucleus to produce a body made only of neutrons with no spaces between; This means that a neutron star is so dense that on Earth, one teaspoonful would weigh a billion tons! http://www.astro.umd.edu/~miller/nstar.html

34. ` C. Pulsar - rotating neutron star (as seen from earth) which sweeps a beam of EMR (usually radio frequencies) past the earth from its poles; some pulsars are believed to rotate thousands of times per second;

35. D. Nova - matter falling onto the surface of a white dwarf from a binary companion explodes from the surface as fusion begins spontaneously on its entire surface area; can recur until whitedwarf dies; http://spaceflightnow.com/news/n0210/12nova/

36. E. Supernova - the final collapse of the outer layers of a supergiant star causes the greatest explosion observed in the universe and the light emitted rivals the light from nearby galaxies (2 types, depending on what causes explosion); http://heasarc.gsfc.nasa.gov/docs/snr.html

37. F. Binary Stars - two stars revolving about a common center of mass; the majority of stars in the universe are part of a multi-star-system; http://zebu.uoregon.edu/~js/ast222/lectures/lec05.html

38. G. Cepheid Variable - star whose luminosity varies regularly due to physical contraction and expansion of its sphere; http://hyperphysics.phy-astr.gsu.edu/hbase/astro/cepheid.html http://scienceworld.wolfram.com/astronomy/CepheidVariable.html

39. VIII. Collections of Stars A. Constellations - asterisms; collections of stars that appear close together in the sky which suggests an object’s or person’s shape; best seen by those who have consumed old grape juice; most stars are not even close together; http://www.astro.wisc.edu/~dolan/constellations/extra/constellations.html#Orion http://www.astro.wisc.edu/~dolan/constellations/java/Antlia.html

40. B. Galaxies - groups of billions of stars that are often hundreds of thousands of light years across, but rotate around a common central axis; there are 3 major types: spiral, elliptical, and irregular; Andromeda galaxy

41. • The Milky Way is part of a group of 22 galaxies called the “Local Cluster” with a diameter of 3 million ly; • The Virgo Cluster contains 1000 galaxies is 50 million ly distant; other “close” galactic clusters can contain as many as 10,000 galaxies; • The Virgo Cluster and the Local Cluster are members of a Super Cluster of galaxies with a diameter of 130 million ly and revolve around its center at a speed of 400 km s-1; • There is even evidence to suggest that clusters of super clusters of galaxies exist; http://csep10.phys.utk.edu/astr162/lect/gclusters/gclusters.html

42. IX. Other Quasar - discovered in 1960; mysterious luminous object which steadily gives off as much light as 1000 galaxies but seems to be much smaller than any known galaxy; very distant (Quasar 3C273 is 3 billion ly’s distant); http://chandra.harvard.edu/xray_sources/quasars.html

43. -COMETS...large masses of frozen gases; • Solar objects orbit the sun in elliptical orbits with Sol at one focus; some orbits are nearly circular (eg., Mars) while others are highly elliptical (eg., Comet Hyakutake...T = 30,000 years); • Between Mars and Jupiter is the Asteroid Belt - a wide band of pebble-to-mountain sized chunks of rock which may be the remains of a destroyed planet or the “precursors” of a planet which never formed;

44. The Solar System

45. E.1.2 Constellations and Stellar Clusters A. Constellations - asterisms; collections of stars that appear close together in the sky and which suggest an object’s or person’s shape; best seen by those who have consumed lots of old grape juice; most stars in a constellation are not even close together;

46. B. Stellar Clusters - a group of stars that are held together by mutual gravitational attraction; the stars all formed from the same nebula at about the same time; there can be from dozens to thousands of stars in a single cluster;

47. C. Galaxies - groups of billions of stars that are often hundreds of thousands of light years across, but rotate around a common central axis; there are 3 major types: spiral, elliptical, and irregular;

48. The Galaxy Zoo Project <http://www.galaxyzoo.org>www.galaxyzoo.org - The Milky Way is part of a group of 22 galaxies called the “Local Cluster” with a diameter of 3 million ly; - The Virgo Cluster contains 1000 galaxies is 50 million ly distant; other “close” galactic clusters can contain as many as 10,000 galaxies; - The Virgo Cluster and the Local Cluster are members of a Super Cluster of galaxies with a diameter of 130 million ly and revolve around its center at a speed of 400 km s-1; - There is even evidence to suggest that clusters of super clusters of galaxies exist; SUPER CLUSTERS http://csep10.phys.utk.edu/astr162/lect/gclusters/gclusters.html

49. E.1.4 Relative Distances in Space THE UNIVERSE - by powers of ten http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html • Stars in a galaxy are not evenly distributed, but the average distance is about the same as the distance between Sol and Alpha Centauri... 1 x 1017 m; • Galaxies form clusters just as stars do, but the average distance between galaxies is about 1 x 1023 m; • Galactic clusters are not evenly distributed, but the average distance between cluster is about 1 x 1014 m;

50. E.1.5 Apparent Motion of Celestial Objects • The visible objects in the night sky exhibit an apparent motion which has them “rise” in the East and set in the West and trace great circular arcs across the sky just as if they are fixed to a giant celestial sphere. This apparent motion is caused by the rotation of the earth on its axis every 24+ hours. • Closer observation of the location of the visible objects finds that some objects remain fixed in place and others move or “wander” about the sky in other than straight lines or even circular arcs. These “wanderers” are the planets (named by the Greeks) and the follow unusual paths, even moving backward (retrograde motion) when compared to the fixed stars. These motions take days, weeks, months, years, decades and even centuries (depending on the planet) to observe. • As earth revolves around the sun, Sol’s position changes with respect to the fixed stars. It moves from 23.5o north of the celestial equator to 23.5o south of the celestial equator and 360o around the equator each year. When it crosses the celestial equator at the Vernal Equinox (March) and Autumnal Equinox (Sept), there are equal periods of day and night. • The moon revolves around the earth in about 30 days...the term month comes from “moonth”...a period of about 30 days. The moon rotates on its axis once every revolution...thus the same side of the moon is always visible from earth. As the moon revolves, its position relative to the sun and earth changes and thus we see the phases of the moon... new moon to full moon to new moon. • The closer stars (< 100 ly) exhibit a proper motion and actually move across the sky in very small increments measured in seconds of arc per year.