1. Foundations of Astronomy: Part 3
Review
Eclipses
(New) Celestial Sphere
Seasons and Geography
Precession of the Equinoxes
Tropical Year vs. Sidereal Year
Math and Astronomy
Significant Figures
Orders of Magnitude
Units and Unit Conversions
Nature of Science
What is Science
Terminology
Scales
Metric System
Everyday Scales
Astronomy Scales

2. Review Question 1: What time of day does the first quarter moon set?
A: 6am
B: noon
C: 6pm
D: midnight
E: Never sets

3. 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
Answer: a

4. 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
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!

5. Review Question 3 A total lunar eclipse occurs
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
Answer: c

6. Review Question 3 A total lunar eclipse occurs
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

7. 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
Moon
Earth

8. Solar Eclipses Diamond ring effect - just before or after total Total
Partial
Annular - why do these occur?

9. Top view, exaggerated ellipse
Moon's orbit tilted compared to Earth-Sun orbital plane:
Sun
Moon
Earth
5.2o
Side view
Moon's orbit slightly elliptical:
Moon
Distance varies by ~12%
Earth
Top view, exaggerated ellipse

10. Types of Solar Eclipses Explained

11. Certain seasons are more likely to have eclipses
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.

12. Geography of Earth Sun and Earth Equator and poles
Tropic of Cancer and Tropic of Capricorn
Artic and Antarctic Circle
Defining Locations
Latitude
Longitude
Albuquerque
35 deg 06 min 39 sec N
106 deg 36 min 36 sec W
Path of Sun

13. Motion of Sun Sunrise and Sunset Position of Sun arc shifts
Farthest North at Summer Solstice
Farthest South at Winter Solstice

14. 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

15. 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 ...

16. The Celestial Sphere
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.
Features:
- Does not rotate with Earth
- Poles, Equator
- Coordinate System
88 Constellations

17. Locations on the Celestial Sphere
Ecliptic
Path of Sun on Celestial Sphere Constellation on Ecliptic are the Zodiac Constellations
Spring and Vernal Equinox
Where Ecliptic crosses Celestial Equator
Winter and Summer Solstice
Turn around points on Ecliptic
Where Sun farthest from Equator
Finding Locations
Right Ascension – like Longitude
Measured from Vernal Equinox in units of time (hours and min)
Declination – like Latitude + North and – South

18. The Earth's rotation axis is tilted with respect to its orbit around the Sun => seasons.
Summer
Winter
Sun low in northern sky
Sun high in northern sky
Scorpius
Day
Night
Orion
Night
Day
Tilt is 23.5o

19. Precession Period 26,000 years!
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
Vega * *
Polaris
Spin axis
Precession Period 26,000 years!

20. Precession Gyroscope Demonstration Video of Precession

21. The Year
Summer
Winter
Day
Night
Orion
Scorpius
Night
Day
The Earth revolves around the Sun in days (“sidereal year”). But the year we use is days (“tropical year”). Why?

22. Scientific Notation
(A shorthand way of writing very large and small numbers, which occur often in astronomy).
We use powers, or exponents, of 10:
= 102 (= 10 x 10)
= 103 (= 10 x 10 x 10)
1,000, = 106
= 101
= 100
= 10 -1
= 10 -4
= 7 x 10 -3
Add the exponents
4000 x 0.002
= (4 x 103) x (2 x 10 -3)
= 8 x 100 = 8

23. 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?

24. Order of magnitude 100 = 102 (= 10 x 10) Order of Magnitude 100 or 2
= 103 (= 10 x 10 x 10) 1,000 or 3
1,000, = ,000,000 or 6
= or 1
= or 0
= or -1
= or -4
= 7 x or -2
Order of magnitude => round to nearest power of 10
Exponent of 10 is order of magnitude

25. Units and Unit Conversions
How many seconds in a year?

26. Clicker Question: How many stars are there in the observable universe?
D: 1042
E: infinite

27. 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?
Terminology
Observations Scientific Statement
Generalizations
Simplifying
Hypothesis
Theory vs. Law

28. 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.

29. Distance Volume 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)

30. Temperature The Celsius Scale: T(oC) = 5/9 [ T(oF) - 32 oF ]
so oF = 0 oC
212 oF = 100 oC
68 oF = 20 oC
The Kelvin Scale:
T(K) = T(oC) oC
"Absolute zero" 0 K = -273 oC

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

32. 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.

33. THE QUEST FOR RESOLUTION
Atmosphere gives 1" limit without corrections which are easiest in radio
Jupiter and Io as seen from Earth
1 arcmin arcsec arcsec arcsec
Simulated with Galileo photo

34. 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?

35. 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)
Moving towards us at about 70 mi/sec – will collide in 4.5 billion years
- 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

36. 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 MEarth
- Mass of Milky Way galaxy: more than 1011 MSun
- Mass of a typical cluster of galaxies: about 1015 MSun

37. 4. Very high and low temperatures:
3. Long ages and times:
- Age of Earth and Solar System: billion years
= 4.5 x 109 years
- Lifetime of stars: about 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