Download Powerpoint - Physics and Astronomy

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
Review Question 1:
What time of day does the first quarter moon
set?
A: 6am
B: noon
C: 6pm
D: midnight
E: Never sets
Review Question 2
Considering the
Moon’s phases,
everyone on Earth sees
a)
b)
c)
d)
the same phase in 24 hours.
different phases in 24 hours.
a lunar eclipse once a month.
different sides of the Moon.
Review Question 2
Considering the
Moon’s phases,
everyone on Earth sees
a)
b)
c)
d)
the same phase in 24 hours.
different phases in 24 hours.
a lunar eclipse once a month.
different sides of the Moon.
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!
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.
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.
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
Solar Eclipses
Diamond ring effect - just before or
after total
Total
Partial
Annular - why do these occur?
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
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 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
Motion of Sun
Sunrise and Sunset
Position of Sun arc shifts
Farthest North at Summer Solstice
Farthest 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 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 ...
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
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
The Earth's rotation axis is tilted with respect to its orbit around
the Sun => seasons.
Summer
Scorpius
Night
Tilt is 23.5o
Winter
Day
Sun high in
northern sky
Sun low in Day
northern sky
Night
Orion
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
Vega
*
* Polaris
Spin axis
Precession Period 26,000 years!
Precession
Gyroscope Demonstration
Video of Precession
http://upload.wikimedia.org/wikipedia/co
mmons/7/7c/Precession_animation_small
_new.gif
The Year
Summer
Scorpius
Night
Winter
Day
Day
Night
The Earth revolves around the Sun in 365.256 days (“sidereal year”).
But the year we use is 365.242 days (“tropical year”). Why?
Orion
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
1000
1,000,000
10
1
0.1
0.0001
0.007
= 102 (= 10 x 10)
= 103 (= 10 x 10 x 10)
= 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
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
1000
1,000,000
10
1
0.1
0.0001
0.007
= 102 (= 10 x 10)
= 103 (= 10 x 10 x 10)
= 106
= 101
= 100
= 10 -1
= 10 -4
= 7 x 10 -3
Order of Magnitude 100 or 2
1,000 or 3
1,000,000 or 6
10 or 1
1 or 0
0.1 or -1
0.0001 or -4
0.01 or -2
Order of magnitude => round to nearest power of 10
Exponent 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?
Terminology
Observations
Generalizations
Simplifying
Hypothesis
Theory vs. Law
Scientific Statement
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 arcminutes
1' = 60" or arcseconds
1" = 1000 mas or milli-arcseconds
Angular Measure
• Full circle contains
360° (degrees).
• Each degree contains
60′ (arc-minutes).
• Each arc-minute
contains 60″ (arcseconds).
• Angular size of an
object depends on actual
size and distance away.
THE QUEST FOR RESOLUTION
Resolution = Observing wavelength / Telescope diameter
Angular
Optical (5000A)
Radio (4cm)
Resolution Diameter Instrument
Diameter Instrument
2mm
Eye
140m
GBT+
1¢
10cm
Amateur Telescope 8km
VLA-B
1²
2m
HST
160km
MERLIN
0.²05
100m
Interferometer
8200km VLBI
0.²001
Atmosphere gives 1" limit without corrections which are easiest in radio
1 arcmin
Jupiter and Io as seen from Earth
1 arcsec
0.05 arcsec
0.001 arcsec
Simulated with Galileo photo
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 MEarth
- 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