Foundations of Astronomy: Part 3 Review

Eclipses(New) Celestial SphereSeasons and GeographyPrecession of the EquinoxesTropical Year vs. Sidereal Year

Math and AstronomySignificant FiguresOrders of Magnitude

Units and Unit Conversions

Nature of ScienceWhat is ScienceTerminology

ScalesMetric SystemEveryday Scales

Astronomy Scales

Review Question 1:

What time of day does the first quarter moon set?

A: 6am

B: noon

C: 6pm

D: midnight

E: Never sets

a) the same phase in 24 hours.

b) different phases in 24 hours.

c) a lunar eclipse once a month.

d) different sides of the Moon.

Considering the Moon’s phases, everyone on Earth sees

Review Question 2

a) the same phase in 24 hours.

b) different phases in 24 hours.

c) a lunar eclipse once a month.

d) different sides of the Moon.

Considering the Moon’s phases, everyone on Earth sees

Review Question 2

The Moon goes through its cycle of phases in about 30

days; the Earth rotates once in only 24 hours.

So everyone has a chance to see the same phase!

a) during the new moon phase.

b) when the Sun blocks the Moon.

c) during the full moon phase.

d) always around the summer solstice.

A total lunar eclipse occurs

Review Question 3

a) during the new moon phase.

b) when the Sun blocks the Moon.

c) during the full moon phase.

d) always around the summer solstice.

A total lunar eclipse occurs

Review Question 3

Eclipses

Lunar Eclipse

When the Earth passes directly between the Sun and the Moon.

Sun Earth Moon

Solar Eclipse

When the Moon passes directly between the Sun and the Earth.

Sun EarthMoon

Solar Eclipses

Total

Diamond ring effect - just before or after total

Partial

Annular - why do these occur?

Moon's orbit tilted compared to Earth-Sun orbital plane:

SunEarthMoon

Moon's orbit slightly elliptical:

Earth

Moon

Side view

Top view, exaggerated ellipse

Distance varies by ~12%

5.2o

Types of Solar Eclipses Explained

Certain seasons are more likely to have eclipses. Solar “eclipse season” lasts about 38 days. Likely to get at least a partial eclipse somewhere. Animation

It's worse than this! The plane of the Moon's orbit precesses, so that the eclipse season occurs about 19 days earlier each year.

Geography of Earth

Sun and Earth

Equator and polesTropic of Cancer and Tropic of CapricornArtic and Antarctic Circle

Defining Locations

LatitudeLongitudeAlbuquerque

35 deg 06 min 39 sec N106 deg 36 min 36 sec W

Path of Sun

Motion of Sun

Sunrise and SunsetPosition of Sun arc shiftsFarthest North at Summer SolsticeFarthest South at Winter Solstice

Finding Location from the Sun

Finding Locations from Sun

Angle of Sun at noon measured from the horizon can give position on Earth

At noon on equinoxes Sun angle gives latitude

Time of noon gives longitude

Zenith is point directly above you

The Sky at Night

What do we see?

The MoonPlanetsPerhaps a meteor shower, comet, or other rare eventStars - about 3000 visiblePatterns of stars - constellations 88 of them Useful for finding our way around the sky, navigating the oceansSatellites, airplanes, clouds, lightning, light pollution ...

The Celestial Sphere

Features:- Does not rotate with Earth- Poles, Equator- Coordinate System

88 Constellations

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.

Locations on the Celestial Sphere

EclipticPath of Sun on Celestial SphereConstellation on Ecliptic are the Zodiac Constellations

Spring and Vernal EquinoxWhere Ecliptic crosses Celestial Equator

Winter and Summer SolsticeTurn around points on EclipticWhere Sun farthest from Equator

Finding LocationsRight Ascension – like LongitudeMeasured from Vernal Equinoxin units of time (hours and min)

Declination – like Latitude+ North and – South

The Earth's rotation axis is tilted with respect to its orbit around the Sun => seasons.

Summer Winter

Scorpius Orion

Tilt is 23.5o

DayNight Day NightSun high in northern sky

Sun low in northern sky

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 (how do we know this?)

Earth

Moon

Spin axis

**Vega Polaris

Precession Period 26,000 years!

Precession

Gyroscope Demonstration

Video of Precessionhttp://upload.wikimedia.org/wikipedia/commons/7/7c/Precession_animation_small_new.gif

Summer Winter

ScorpiusOrionDayNight Day Night

The Year

The Earth revolves around the Sun in 365.256 days (“sidereal year”). But the year we use is 365.242 days (“tropical year”). Why?

Scientific Notation

(A shorthand way of writing very large and small numbers, which occur often in astronomy).

We use powers, or exponents, of 10:

100 = 102 (= 10 x 10) 1000 = 103 (= 10 x 10 x 10)1,000,000 = 106 10 = 101 1 = 100 0.1 = 10 -1 0.0001 = 10 -4 0.007 = 7 x 10 -3

4000 x 0.002 = (4 x 103) x (2 x 10 -3)= 8 x 100 = 8

Add the exponents

Examples:The mass of an electron

9.11 x 10-31 kg

The mass of the Earth

5.97 x 1024 kg

How many times more massive is the Earth than an electron?

Order of magnitude

100 = 102 (= 10 x 10) Order of Magnitude 100 or 21000 = 103 (= 10 x 10 x 10) 1,000 or 31,000,000 = 106 1,000,000 or 610 = 101 10 or 11 = 100 1 or 00.1 = 10 -1 0.1 or -10.0001 = 10 -4 0.0001 or -40.007 = 7 x 10 -3 0.01 or -2

Order of magnitude => round to nearest power of 10Exponent of 10 is order of magnitude

Units and Unit Conversions

How many seconds in a year?

Clicker Question:

How many stars are there in the observable universe?

A: 1012

B: 1022

C: 1032

D: 1042

E: infinite

Nature of Science

What were the 3 most interesting things you found in the Einstein’s Big Idea Video?

What is Science?How is it different from other areas of human activity?How is science done?Hypothesis vs. Theory

Discuss 3 examples of science from the video?

TerminologyObservations Scientific StatementGeneralizationsSimplifyingHypothesisTheory vs. Law

Foundations of Astronomy

The Metric System(used by scientists and foreigners)

Mass

1 kilogram (kg) = 1000 grams (g)

28 g = 1 ounce

If your mass is 220 lbs, it's also 100 kg.

We tend to use mass and weight interchangeably, but weight depends on gravity.

Distance

1 meter (m) = 100 centimeters (cm) = 39.4 inches(slightly longer than a yard - your professor is 1.8 m in height)

1 cm = 0.39 inches

Volume

1 cubic centimeter or 1 cm3 = 0.06 cubic inches(about the size of a sugar cube)

Temperature

The Celsius Scale:

T(oC) = 5/9 [ T(oF) - 32 oF ]

so 32 oF = 0 oC 212 oF = 100 oC 68 oF = 20 oC

The Kelvin Scale:

T(K) = T(oC) + 273 oC

"Absolute zero" 0 K = -273 oC

Angular Measure

90o

20o

360o, or 360 degrees, in a circle.

1o = 60' or arcminutes1' = 60" or arcseconds1" = 1000 mas or milli-arcseconds

• 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.

Angular Measure

THE QUEST FOR RESOLUTION

Jupiter and Io as seen from Earth1 arcmin 1 arcsec 0.05 arcsec 0.001 arcsec

Simulated with Galileo photo

Atmosphere gives 1" limit without corrections which are easiest in radio

Scales of your world

Think about

• How big your car is?

• How your house/apartment is?

• How big Albuquerque is?

• How big the US is?

• How far away the farthest place you have travelled is?

• How massive a very big man-made object is?

In astronomy, we deal with:

1. Vast distances• - Radius of Earth = 6,400 km = 6.4 x 106 m

- Distance to Moon =384,000 km = 3.8 x 108 m

•- Distance to Sun = 1.5 x 1011 m = 23,500 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 1012 km. Speed of light c = 3 x 108 m/sec)

• - Size of Milky Way Galaxy: about 100,000 light years

• - Distance to Andromeda Galaxy = 2.5 million light years

- Distance to nearest cluster of galaxies (Virgo Cluster): 5 x 107 light years

2. Huge masses:

- Mass of Earth = 6 x 1024 kg = 6 x 1027 g = 1 MEarth

(or 6000 billion billion tons)

- Mass of Sun = 2 x 1030 kg = 2 x 1033 g = 1 MSun

= 1 "Solar Mass" = 333,000 M

Earth

- Mass of Milky Way galaxy: more than 1011 MSun

- Mass of a typical cluster of galaxies: about 1015 MSun

3. Long ages and times:

- Age of Earth and Solar System: 4.5 billion years = 4.5 x 109 years

- Lifetime of stars: about 106 - 1010 years

-Age of universe: about 1010 years

4. Very high and low temperatures:

- An interstellar "molecular cloud": T 10 K

- Center of Sun: T = 1.5 x 107 K