Announcements Read 2.1 (Magnitude & Flux), 3.1, 3.2, 3.3 In-class Quiz #1 on Tuesday, January 29. Homework #2 due in class on Thursday, January 31. Disability Services is in need of a note taker for this class. If you are interested, please email notes@admin.umass.edu with your name, student ID and the course info (Astronomy 100, Section 1, Professor Katz). Disability Services staff will contact you to confirm and provide you instructions. You may earn 1 undergraduate academic credit (practicum EDUC 398NT) or 45 hours of community service for your efforts.
Now on to scales in the Cosmos Let s change scale by TWO orders of magnitude at a time and see what happens.
52 feet across
1 mile across = 5280 feet =1.6 km
160 kilometers across 1 mile = 1.61 kilometers Infrared photo
12,756 km
1,600,000 km =1.6 x 106 km Moon
1.6x108 km =1.6x1011m 1AU = 1.5x1011 m AU is a distance unit
1.6 x 1010 km, or a trillion (1012) times wider than the first picture! 100 AU
10,000 AU Stars are so far apart from each other! If the Sun is a golf ball in NYC, the nearest star is a golf ball in Chicago!!!
106 AU = 17 ly 1 ly =63,000 AU = 1013 km
1700 ly
170,000 ly
1.7 x 107 ly The local group of galaxies
1.7 x 109 ly
A Sense of Space 1. The Sun would hold 1.3 million Earths, i.e. the radius of the Sun is about 100 times that of the Earth. 2. There are ~100 billion "Suns" in a galaxy like our own Milky Way Galaxy. 3. Astronomers can see billions of galaxies.
If the Sun were a grapefruit on one side of the room, what would be Earth? 1) A poppy seed on the other side. 2) Another grapefruit on the other side. 3) A poppy seed in my office. 4) An apple on the other side.
If the Sun were a grapefruit on one side of the room, what would be Earth? 1) A poppy seed on the other side. 2) Another grapefruit on the other side. 3) A poppy seed in my office. 4) An apple on the other side.
What would then be the nearest star? 1) A poppy seed in downtown. 2) A poppy seed on the west coast. 3) A grapefruit in downtown Amherst. 4) A grapefruit on the west coast.
What would then be the nearest star? 1) A poppy seed in downtown. 2) A poppy seed on the west coast. 3) A grapefruit in downtown Amherst. 4) A grapefruit on the west coast.
Angular Size The Sun is physically 400 times larger than the Moon. Why is their angular size is the same?
S D rad = S/D Angle diameter (in radians) = diameter/distance Full circle = 2 (in radians)=360 degrees=360o 1o=60 arminutes = 60 1 = 60 arcseconds = 60 ; 1 rad = 206,264.81
Angular Size Some Examples: Horizon to zenith (point overhead) Your fist at arm's length Your fingernail at arm's length Sun or Moon seen from Earth Smallest detail visible to naked eye 90o 10o 1o = 60' 0.5o = 30' 1' = 60'' Smallest detail visible by a single telescope from surface: 1'' Angular size of Pluto: 0.15 Betelgeuse (largest star) seen from Earth 0.004'' Earth's
The Orion Constellation
Constellations 88 official constellations divide the sky into areas with clearly defined boundaries. The names of constellations are in Latin. But most bright star names are derived from ancient Arabic. The original constellations were invented by farmers over 5000 years ago. Remember that the constellations are not real! They are just imaginative figures invented by ancient cultures.
Projection Big Dipper ---- an asterism
The Sky and its Cycles Goals: To describe and locate objects in the sky. To understand the apparent motions of celestial objects. To introduce the seasons.
What objects can you see with your naked eye?
What objects can you see with your naked eye? Moon planets sun comets Stars Milky way galaxies
What objects can you see with your naked eye? Moon planets sun comets Stars Milky way galaxies solar system move not solar system do not move
How long to go all the way around? 1 day b. 1 week c. 1 month d. 1 year
How long to go all the way around? 1 day b. 1 week c. 1 month d. 1 year
How Do We Locate Objects on the Sky? The Celestial Sphere (C.S.) Stars, planets, the Sun, external galaxies, are at different distances from us, yet for studying patterns in the sky, we represent them in projection onto the C.S.
There are two ways to think about the motion of the sky: - the C.S. rotates - or the Earth rotates while the sky sits still. Sometimes one works better than the other
The altitude of Polaris above the horizon is approximately the same as the observer's latitude in the Northern Hemisphere.
The Motions of Earth 1. The Earth rotates this leads to day and night. 2. The Earth revolves around (orbits) the Sun this leads to the seasons because of the tilt of the earths axis. 3. The Earth and Sun revolve around (orbit) the center of the Galaxy. 4. The Galaxy moves through the Universe.
Cycles of the Sky Earth's rotation causes the sun and stars to rise in the east and set in the west daily. But not everywhere! Near the poles, the sun rises and sets every half year, and circumpolar constellations such as Ursa Major, never set. What other cycles do you know?