Do Now What do you see?

Chapter 1 Charting the Heavens

Units and Scales Greek letters Scientific notation (powers of 10) SI Units (mks system) Fundamental constants

Sizes/Scales in the Universe

Important Metric Prefixes Nano = 1/1,000,000,000 Micro = 1/1,000,000 Milli = 1/1000 Centi = 1/100 Kilo = 1000 Mega = 1,000,000 Giga = 1,000,000,000 Tera = 1,000,000,000, Everything in Science is Metric

SI UNITS Measurement system used all over the world except for 3 countries (US, Liberia & Burma) Base units are the meter(m), kilogram(kg) & second(s) for length, mass & time Other units made by combining these, e.g., velocity in m/s; acceleration in m/s 2 ; force in kgm/s 2 (= Newton) ; energy in N·m (= Joule); power in J/s (= Watt)

Ordinary decimal notation Scientific notation (normalized) 3003×10 2 4,0004×10 3 5,720,000, ×10 9 − −6.1×10 −9 Scientific Notation Numbers are written in form of a x 10 b

Multiplication When multiplying numbers written in scientific notation…..multiply the first factors and add the exponents. Sample Problem: Multiply (3.2 x ) (2.1 x 10 5 ) Solution: Multiply 3.2 x 2.1. Add the exponents Answer: 6.7 x 10 2

Division Divide the numerator by the denominator. Subtract the exponent in the denominator from the exponent in the numerator. Sample Problem: Divide (6.4 x 10 6 ) by (1.7 x 10 2 ) Solution: Divide 6.4 by 1.7. Subtract the exponents Answer: 3.8 x 10 4

Addition and Subtraction To add or subtract numbers written in scientific notation, you must….express them with the same power of ten. Sample Problem: Add (5.8 x 10 3 ) and (2.16 x 10 4 ) Solution: Since the two numbers are not expressed as the same power of ten, one of the numbers will have to be rewritten in the same power of ten as the other. 5.8 x 10 3 =.58 x 10 4 so.58 x x 10 4 =? Answer: 2.74 x 10 4

Fundamental Constants Physical quantities that are generally believed to be both universal in nature and constant in time. Examples: QuantitySymbolValue Relative Standard Uncertainty speed of light in vacuum c m/s 1 defined Newtonian constant of gravitation G × m 3 /kg·s × 10 −4 Planck constanth × 10 −34 J·s5.0 × 10 −8 proton massmpmp × 10 −27 kg5.0 × 10 −8

Figure 1-1 Earth

Figure 1-2 The Sun sunspots Sunspots are About the size of the Earth!

Figure 1-3 Spiral Galaxy (similar to our Milky Way) Latest NewsLatest News: Milky way thickness was thought to be 6000 ly. Now seems to be 12,000 ly.

Figure 1-4 Galaxy Cluster

1.1 Our Place in Space ● Earth is unique because we live here ● Universe: totality of all space, time, matter, and energy

1.1 Our Place in Space ●Astronomy: study of the universe ●Scales are very large: measure in light-years, the distance light travels in a year—about 10 trillion miles ●The Known Universe AMNH 2010The Known Universe

1.1 Our Place in Space ● This galaxy is about 100,000 light-years across

1.3 The “Obvious” View Simplest observation: Look at the night sky About 3000 stars visible at any one time; distributed randomly but human brain tends to find patterns

1.3 The “Obvious” View Group stars into constellations: Figures having meaning to those doing the grouping Useful: Polaris, which is almost due north; Heliacal rise time for SiriusHeliacal rise time for Sirius Not so useful: Astrology, which makes predictions about individuals based on the star patterns at their birthAstrology

1.3 The “Obvious” View Stars that appear close in the sky may not actually be close in space.

1.3 The “Obvious” View The celestial sphere: Stars seem to be on the inner surface of a sphere surrounding the Earth They aren’t, but can use two- dimensional spherical coordinates (similar to latitude and longitude) to locate sky objectsspherical coordinates Right Ascension & Declination

More Precisely 1-2: Celestial Coordinates ● Declination: degrees north or south of celestial equator ● Right ascension: measured in hours, minutes, and seconds eastward from position of Sun at vernal equinox ● Rotating Sky Explorer Rotating Sky Explorer ●Houston: 29.5°N 95°W

More Precisely 1-1: Angular Measure ● Full circle contains 360° (degrees) ● Each degree contains 60′ (arc-minutes) ● Each arc-minute contains 60′′ (arc- seconds) ● Angular size of an object depends on actual size and distance away

Do Now What do you see?

1.4 Earth’s Orbital Motion ● Daily cycle, noon to noon, is diurnal motion —solar day ● Stars aren’t in quite the same place 24 hours later, though, due to Earth’s rotation around Sun; when they are, one sidereal day has passed

1.4 Earth’s Orbital Motion 12 constellations Sun moves through during the year are called the zodiac; path is eclipticzodiac Ophiuchus is "13th" sign of the zodiac

1.4 Earth’s Orbital Motion Seasonal changes to night sky are due to Earth’s motion around Sun

1.4 Earth’s Orbital Motion ●Ecliptic is plane of Earth’s path around Sun; at 23.5° to celestial equator ●Northernmost point (above celestial equator) is summer solstice; southernmost is winter solstice; points where path cross celestial equator are vernal and autumnal equinoxes ●Combination of day length and sunlight angle gives seasons ●Time from one vernal equinox to next is tropical year Motion of sun simulator

1.4 Earth’s Orbital Motion Precession: rotation of Earth’s axis itself; makes one complete circle in about 26,000 years

1.4 Earth’s Orbital Motion Time for Earth to orbit once around Sun, relative to fixed stars, is sidereal year Tropical year follows seasons; sidereal year follows constellations—in 13,000 years July and August will still be summer, but Orion will be a summer constellation

1.5 Astronomical Timekeeping Solar noon: when Sun is at its highest point for the day Drawbacks: length of solar day varies during year; noon is different at different locations

1.5 Astronomical Timekeeping Define mean (average) solar day—this is what clocks measure. Takes care of length variation. Also define 24 time zones around Earth, with time the same in each one and then jumping an hour to the next. Takes care of noon variation.

1.5 Astronomical Timekeeping World time zones

Do Now Why do you think the Moon looks different at different times of the month?

1.5 Astronomical Timekeeping Lunar month (complete lunar cycle) doesn’t have whole number of solar days in it, and tropical year doesn’t have whole number of months Current calendar has months that are close to lunar cycle, but adjusted so there are 12 of them in a year

1.6 Motion of the Moon Moon takes about 29.5 days to go through whole cycle of phases—synodic month Phases Phases are due to different amounts of sunlit portion being visible from Earth Time to make full 360° around Earth, sidereal month, is about 2 days shorter

Lunar Phases Rising & Setting Times

1.6 Motion of the Moon Eclipses occur when Earth, Moon, and Sun form a straight line

1.6 Motion of the Moon Eclipses don’t occur every month because Earth’s and Moon’s orbits are not in the same plane

1.6 Motion of the Moon Lunar eclipse: ● Earth is between Moon and Sun ● Partial when only part of Moon is in shadow ● Total when it all is in shadow

1.6 Motion of the Moon Solar eclipse: Moon is between Earth and Sun ●Partial when only part of Sun is blocked ●Total when it all is blocked ●Annular when Moon is too far from Earth for total

1.7 The Measurement of Distance Triangulation: Measure baseline and angles, can calculate distance

1.7 The Measurement of Distance Parallax: Similar to triangulation, but look at apparent motion of object against distant background from two vantage points. Edmund Halley was the first to notice stellar parallax.

1.7 The Measurement of Distance Measuring Earth’s radius: Done by Eratosthenes about 2300 years ago; noticed that when Sun was directly overhead in one city, it was at an angle in another. Measuring that angle and the distance between the cities gives the radius. Carl Sagan explains Erathosthenes

More Precisely 1-3: Measuring Distances with Geometry Converting baselines and parallaxes into distances. Parallax second = 1 parsecParallax second = 1 parsec (1/3600 of a degree with parallax of 1 AU)

More Precisely 1-3: Measuring Distances with Geometry Converting angular diameter and distance into size