1. The syllabus I handed out had the wrong dates for the exams (the slides had them right). They will be on Oct 5 and Nov 9

2. PHYS 3380 - Astronomy Homework Set # 1 8/26/15 Due: 9/2/15 Chapter 2 Review questions: 8, 10 Discussion question 2 Problems 3,5,9 1. Rigel (  Orionis) has a declination of -8  12’ 6” and a right ascension of 5h 14m 32.3s. It is at an elevation of 34  at the meridian, looking to the north. What is your latitude? 2. You have a sundial that tells you that your solar local time is 5:15 PM. Your watch tells you that the Greenwich Mean Time is 10:00 hours. What is your longitude?

3. PHYS 3380 - Astronomy Constellations Constellations - groupings of stars named after mythical heroes, gods, and mystical beasts - made up over at least the last 6000 years - maybe more - used to identify seasons: - farmers know that for most crops, you plant in the spring and harvest in the fall. - in some regions, not much differentiation between the seasons. - different constellations visible at different times of the year - can use them to tell what month it is. For example, Scorpius is only visible in the northern hemisphere's evening sky in the summer. - many of the myths associated with the constellations thought to have been invented to help the farmers remember them - made up stories about them

4. PHYS 3380 - Astronomy In modern world - constellations redefined so now every star in the sky is in exactly one constellation. In 1929, the International Astronomical Union (IAU) adopted official constellation boundaries that defined the 88 official constellations that exist today. asterisms - less formally defined groupings - Big Dipper - part of Ursa Major - Start clusters - Beehive, Pleiades, etc - Orion’s belt - Northern Cross - formed by the leading stars of the constellation Cygnus Constellations Western culture constellations originated in Mesopotamia over 5000 years ago- added to by Babylonian, Egyptian, and Greek astronomers - current list is based on those listed by the Roman astronomer, Claudius Ptolemy (~140 AD)

5. PHYS 3380 - Astronomy Picture at right shows a start chart of the region around the constellation Orion. Picture at the left is an ornate star chart printed in 1835 - shows the great hunter Orion. He is holding a lion's head instead of his traditional bow or shield. He is stalking Taurus, the Bull in the upper right hand corner. Behind him, his faithful dog, Canis Major, is chasing Lepus, the Hare.

6. PHYS 3380 - Astronomy The Orion Nebula

7. PHYS 3380 - Astronomy Nebulae Nebula - an interstellar cloud of dust, hydrogen gas and plasma. One of the most beautiful sights in the universe Birthplaces of stars Planetary nebulae Supernova remnants

8. PHYS 3380 - Astronomy The Orion Nebula Located in the sword of the constellation Orion.

9. PHYS 3380 - Astronomy The Orion Nebula

10. PHYS 3380 - Astronomy Proplyds or Proto Solar Systems in the Orion Nebula

11. PHYS 3380 - Astronomy Gaseous Pillars - Stellar Nursery

12. PHYS 3380 - Astronomy Star Names Brightest stars named thousands of years ago - most come from ancient Arabic Astronomers now use Bayer designations for the brighter stars - introduced by Johann Bayer in his star atlas Uranometria in 1603 - consists of a Greek letter followed by the genitive (in Latin) of the name of the constellation in which the star lies: Aries → Arietis; Taurus → Tauri; Gemini → Geminorum; Virgo → Virginis; Libra → Librae; Pisces → Piscium; Lepus → Leporis. - brightest star of the constellation given the designation Alpha, the next brightest Beta, and so on. Flamsteed designations (introduced by John Flamsteed in 1712) - used when no Bayer designation exists - use numbers instead of Greek letters. Numbers were originally assigned in order of increasing right ascension within each constellation - due to the effects of precession they are now slightly out of order in some places.

13. PHYS 3380 - Astronomy Magnitude Scale Brightness of stars specified with the magnitude system. Devised by Greek astronomer Hipparchus (~150 BC) devised - brightest stars into the first magnitude class, the next brightest stars into second magnitude class, until all of the visible stars grouped into six magnitude classes. The dimmest stars were of sixth magnitude. - therefore based on how bright a star appeared to the unaided eye. By 19th century technology developed to objectively measure a star's brightness - magnitude system refined and quantified - they thought that the eye sensed differences in brightness on a logarithmic scale so a star's magnitude is not directly proportional to the actual amount of energy you receive. - established a magnitude scale in which a difference of 5 magnitudes corresponds to a factor of exactly 100 times in intensity Some objects go beyond Hipparchus' original bounds of magnitude 1 to 6 - bright objects can have magnitudes of 0 or even negative numbers and very faint objects have magnitudes greater than +6.

14. PHYS 3380 - Astronomy The apparent brightness of a star depends on two things: - How much light is it emitting: luminosity (L) [watts] ~ r 2 T 4 - How far away is it: distance (d) [meters] App Bright = L / 4  d 2 Apparent magnitude: - Apparent brightness of a celestial body based on a logarithmic scale of luminosity. - This scale runs backwards - the bigger the number, the fainter the star: brightest stars are #1, next brightest are #2, etc. - Magnitude scale:1 is 2.5:1 2 is 6.3:1 5 is 100:1 - Each difference of 5 in magnitude corresponds to 100 in brightness The Modern Magnitude System

15. Luminosity of Stars Apparent brightness/apparent magnitude refers to the amount of a star’s light which reaches us per unit area. - the farther away a star is, the fainter it appears to us - how much fainter it gets obeys an inverse square law - its apparent brightness decreases as the (distance) 2 Luminosity – the total amount of power radiated by a star into space.

16. PHYS 3380 - Astronomy Apparent Magnitude Absolute Magnitude Equivalent to the apparent magnitude if star were placed 10 parsecs (32.6 light years) from sun.

17. PHYS 3380 - Astronomy The Earth rotates about its axis once per day - one rotation equals one day. The axis goes through the north and south poles and through the center of the Earth. It rotates counterclockwise when looking down on the north pole which means that the sun rises in the east and sets in the west. Rotation

18. PHYS 3380 - Astronomy The Rotation of the Earth From Space

19. PHYS 3380 - Astronomy Earth’s rotation causes the stars - the celestial sphere - to appear to rotate around the Earth. Viewed from outside, the stars (and the Sun, Moon, and planets) therefore appear to make simple daily circles around us. The red circles represent the apparent daily paths of a few selected stars.

20. PHYS 3380 - Astronomy The Celestial Sphere Envisioned by the ancients, the celestial sphere had Earth at the center with the stars emblazoned on the sphere. They thought the stars rose and set because the celestial sphere (the sky) rotated, carrying the stars from east to west. All stars appear to move around two points on the celestial sphere, the north and south celestial poles—projections of earth’s axis of rotation. Earth's equator projected on the celestial sphere becomes the celestial equator.

21. PHYS 3380 - Astronomy Our lack of depth perception when we look into space creates the illusion that the Earth is surrounded by a celestial sphere. Thus, stars that appear very close to one another in our sky may actually lie at very different distances from Earth.

22. PHYS 3380 - Astronomy A model of the celestial sphere shows the patterns of the stars, the borders of the 88 official constellations, the ecliptic, and the celestial equator and poles.

23. PHYS 3380 - Astronomy Latitude and Longitude We can locate any place on the Earth's surface by its latitude and longitude. Latitude measures angular distance north or south of the equator. Longitude measures angular distance east or west of the prime meridian (which passes through Greenwich, England). Dallas: latitude = 32.78 º N longitude = 96.78º W

24. PHYS 3380 - Astronomy Zenith is the point directly overhead, nadir is the point directly underneath. The meridian is the line drawn from the horizon in the south through zenith to the horizon in the north.

25. PHYS 3380 - Astronomy A circumpolar constellation never rises or sets - they are always visible. Your latitude determines the portion of the celestial sphere visible in your sky and what constellations/stars are circumpolar. (a) A Northern Hemisphere sky. (b) A Southern Hemisphere sky. At what latitude would you see the entire sky?

26. PHYS 3380 - Astronomy The Earth's rotation causes stars to trace daily circles around the sky. The north celestial pole lies at the center of the circles. Over the course of a full day, circumpolar stars trace complete circles, and stars that rise in the east and set in the west trace partial circles. Here, the time exposure lasted about 6 hours - we see only about one-quarter of each portion of the full daily path. Star Trails The Northern Hemisphere The Southern Hemisphere

27. PHYS 3380 - Astronomy Finding the Celestial Poles You can always find north using the North Star. Polaris can be found using the big dipper. Draw a line through the two “pointer” stars at the end of the big dipper and follow it upwards from the dipper about four outstretched hand’s width. The big dipper is circumpolar in the US so is always above the horizon. The south celestial pole can be found using the Southern Cross. There is no “South Star”

28. PHYS 3380 - Astronomy The Big and Little Dippers

29. PHYS 3380 - Astronomy Motion of the Night Sky Animation

30. PHYS 3380 - Astronomy The height in degrees of the north star above the horizon is the same as your latitude.

31. PHYS 3380 - Astronomy  The angle  between the horizon and Polaris is the latitude of the observer. If Dallas is at 33º latitude, where is Polaris in the sky? Where is it at the Equator?

32. PHYS 3380 - Astronomy Angular Size Distances in the sky measured by angular distance: Minute of arc = 1/60th of a degree Second of arc = 1/3600th of a degree Angular diameter - angular distance from one side of an object to the other

33. PHYS 3380 - Astronomy Earth travels around the sun (orbits) once per year in the same direction it rotates. It’s orbit is not quite a perfect circle - it is elliptical. The location in the orbit of the minimum and maximum distances from the Sun are called perihelion and aphelion. The plane of the orbit is called the ecliptic. Revolution

34. PHYS 3380 - Astronomy Ecliptic Plane The Earth’s axis is currently tilted 23.5º to the ecliptic. It varies over time between 22º and 25º due the the gravitational forces from Jupiter and the other planets. Earth’s Axial Tilt

35. PHYS 3380 - Astronomy The axis remains at the same tilt angle - pointed at Polaris - throughout the orbit because of conservation of angular momentum. The ecliptic plane is the plane of the Earth’s orbit. Looking from the Earth, it is the apparent path of the Sun (and planets) in the sky.

36. PHYS 3380 - Astronomy The Relationship of the Celestial Equator and the Ecliptic Plane

37. PHYS 3380 - Astronomy The Zodiac The Sun appears to move steadily eastward along the ecliptic, through the constellations of the zodiac. As Earth orbits the Sun, we see the Sun against the background of different zodiac constellations at different times of year. For example, on August 21 the Sun appears to be in the constellation Leo. Defines astral calendar.

38. PHYS 3380 - Astronomy Sun’s Path Through the Zodiac

39. PHYS 3380 - Astronomy Celestial Sphere The apparent Sphere of the sky Celestial Poles The points about which the celestial sphere appears to rotate Celestial Equator Projection of the Earth’s equator on the celestial sphere EclipticApparent annual path of the sun on the celestial sphere