Please turn off cell phones & laptops - thanks! panda.unm.edu/courses/sanfratello/SP09/astro101.html Remember - Read syllabus and schedule (contains links to lecture notes, textbook reading assignments and suggested problems from the text.)‏

Astronomy Picture of the Day

What properties of physical objects would you expect to be important in Astronomy?

Mass Size Distance from Earth Temperature Speed and Velocity Brightness (Luminosity)‏ Age Chemical composition

Properties of Matter Mass (How much “stuff” there is)‏ 1 kilogram (kg) = 1000 grams (g) = 2.2 lbs We tend to use mass and weight interchangeably, but weight depends on gravity.

“Massive”

Difference between Mass and Weight: Mass of cat on Earth = Mass of cat on Moon BUT, Weight of cat on Earth = 18lbs Weight of cat on Moon = 18/6 lbs = 3lbs

Distance 1 meter (m) = 100 centimeters (cm)‏ = 39.4 inches (slightly longer than a yard)‏ A way to measure the distance to far astronomical objects is using ANGULAR measures – parallax

Volume (How much space something takes up)‏ 1 cm 3 = 0.06 cubic inches (about the size of a sugar cube)‏ 2 cm 1 cm 2 cm 2 cm x 1cm x 2 cm = 4 cm 3

Density (How much stuff is concentrated in an object) Density = Mass (g / cm 3 )‏ Volume Densities of Common Substances Balsa Wood 0.13 g / cm 3 Gasoline 0.7 Water 1.0 Polystyrene 1.05 Average Rock 2.4 Glass 2.6 Ceramic 4.6 Iron 7.9 Lead 11.3 Gold 19.3

Temperature (How hot something is)‏ The Kelvin Scale: T(K) = T( o C) o C "Absolute zero" 0 K = -273 o C At what temperature (in Kelvin) does water freeze? Boil?

Speed and Velocity Speed – how fast something is moving Velocity – speed + direction = a vector quantity - an object can have the same speed but by changing its direction have a different velocity.

Angular Measures 90 o 20 o 360 o, or 360 degrees, or 360 "arc degrees" in a circle. 1 o = 60' or arcminutes 1' = 60" or arcseconds

Angular Measure

Scientific Notation (A shorthand way of writing large numbers, which occur often in astronomy). We use powers, or exponents, of 10: 100 = 10 2 (= 10 x 10) 1000 = 10 3 (= 10 x 10 x 10)‏ 1,000,000 = = = = = = 7 x x = (4 x 10 3 ) x (2 x )‏ = 8 x 10 0 = 8 Add the exponents

Powers of Ten Video

Question Why is looking at a distant astronomical object like looking into its past?

Scale of the Universe Speed of light –186,000 miles/sec –300,000 km/sec Light-year (LY)‏ –Distance light travels in one year ~ 63,200 AU ~ 6 trillion miles!

The Constellations Northern constellations named for figures in Greek myth Attempt to understand heavens Astronomical Landmarks Are the stars in a constellation all at about the same distance from the Earth?

The Constellation Orion

The Celestial Sphere An ancient concept, as if all objects at same distance. But to find things on sky, don't need to know distance, so still useful today.

The "Solar Day" and the "Sidereal Day" Solar Day How long it takes for the Sun to return to the same position in the sky (24 hours). Sidereal Day How long it takes for the Earth to rotate 360 o on its axis. These are not the same! Which is longer? Why? (Demo)‏

One solar day later, the Earth has rotated slightly more than 360 o. A solar day is longer than a sidereal day by 3.9 minutes (24 hours vs. 23 hours 56 minutes seconds). Difference due to rotation and revolution of Earth!

What causes the seasons?

Seasons

Summer Winter In winter, sunlight is spread out more thinly across the ground => each bit of ground receives less radiation => cooler Seasons caused by tilt of Earth’s axis of rotation. Earth is farthest from sun during summer!

Precession What causes precession? How long does one cycle take?

Precession The Earth has a bulge. The Moon "pulls down" on the side of the bulge closest to it, causing the Earth to wobble on its axis. Earth Moon Spin axis * * Vega Polaris Precession Period 26,000 years!