Astronomy 101 ● Instructor: T. Howard ● Text: Astronomy, 7 th ed., Chaisson & Macmillan ● Course outline: see Syllabus ● Class website: ● Office hours: by appointment, see me before/after class

A Good Time to Study Astronomy Recent and ongoing planetary missions Detection and study of exosolar planets (planets around other stars) New ideas and questions about the very nature of the Universe Latest Nobel Prize awarded for detection of accelerating expansion of the Universe (?)

Figure 0.1 NASA; J. Lodrigus; NOAA

Figure 1.3 © 2013 Pearson Education, Inc.

Asteroid Eros (closeup) (from the NEAR mission) Asteroid Gaspra (u. left), Phobos, Deimos (bottom)

NGC 4013

Foundations of Astronomy The Metric System (used by scientists and foreigners) Mass 1 kilogram (kg) = 1000 grams (g) 100 kg = 220 lbs We tend to use mass and weight interchangeably, but weight depends on gravity. Distance 1 meter (m) = 100 centimeters (cm) 1 m = 1.1 yards (approx.) 1 cm = 0.4 inches (approx.) Volume 1 cubic centimeter or 1 cm 3 (about the size of a sugar cube)

Density Density = Mass (g / cm 3 ) Volume Densities of Common Substances Balsa Wood 0.13 g / cm 3 Oak 0.7 Water 1.0 Average Rock 2.4 Iron 7.9 Lead 11.3 Gold 19.3

Temperature The Celsius Scale: 0 o C = freezing point of water ( = 32 F) 100 o C = boiling point of water ( = 212 F) The Kelvin Scale: T(K) = T( o C) o C "Absolute zero" 0 K = o C

Angles 90 o 20 o 360 o, or 360 degrees, in a circle. 1 o = 60' or arcminutes 1' = 60" or arcseconds 1" = 1000 mas or milli-arcseconds

Scientific Notation Powers, or exponents, of 10: 100 = 10 2 (= 10 x 10) 1000 = 10 3 (= 10 x 10 x 10) 10 = = = = 7 x x 0.002= (4 x 10 3 ) x (2 x ) = 8 x 10 0 = 8 Add the exponents

In astronomy, we deal with: 1. Vast distances - Radius of Earth = 6400 km = 6.4 x 10 8 cm - Distance to Sun = 1.5 x cm = Earth radii = 1 Astronomical Unit (AU) - Distance to next nearest star (Proxima Centauri): 270,000 AU = 4.3 "light years" (light year: distance light travels in one year, 9.5 x km. Speed of light: c = 3 x 10 8 m/sec) - Size of Milky Way Galaxy: about 100,000 light years - Distance to next large galaxy (Andromeda): 2 x 10 6 light years

2. Huge masses: - Mass of Earth = 6 x kg = 6 x g = 1 M Earth (or 6000 billion billion tons) - Mass of Sun = 2 x kg = 2 x g = 1 M Sun = 1 "Solar Mass" = 333,000 M Earth - Mass of Milky Way galaxy: 6 x M Sun

3. Long ages and times: - Age of Earth and Solar System: 4.5 billion years = 4.5 x 10 9 years - Lifetime of stars: about years - Age of universe: about years 4. Very high and low temperatures: - An interstellar "molecular cloud": T = 10 K - Center of Sun: T = 1.5 x 10 7 K

What is the relationship of Astronomy to: -- Physics ? -- Chemistry ? -- Math ? -- Biology ?

Phases of Astronomy as a Science – Understanding motions of moon planets Cataloguing and Classifying Stars, Nebulae Using Physics and Chemistry to explain stars, Nebulae, and Galaxies Trying to explain the Size, Shape, and Behavior of the Universe as a Whole Searching for Life Elsewhere in the Universe Exploring the Solar System Directly

Chapter Opener 0

The Sky at Night What do we see? The Moon Planets Perhaps a meteor shower, comet, or other rare event Stars - about 3000 visible Patterns of stars - constellations 88 of them Useful for finding our way around the sky, navigating the oceans Satellites, airplanes, clouds, lightning, light pollution...

Figure 0.3

The Celestial Sphere Features: - Does not rotate with Earth - Poles, Equator - Coordinate System An ancient concept, as if all objects at same distance. But to find things on sky, don't need to know their distance, so still useful today.

Figure 0.6

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!

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).

Figure 0.7a

Figure 0.7b

Ancient cultures observed the sky Egypt...

... ancient Britons native Americans...