#### Transcript Document

```ASTR 1030 Prologue - Scientific Notation
• writing large (or small) numbers in
powers of 10
• used for simplicity
Examples:
1 = 100
10 = 1 x 101 = 101
100 = 10 x 10 = 1 x 102 = 102
5000 = 5 x 1000 = 5 x 10 x 10 x 10 = 5 x 103
75000 = 7.5 x 10000 = 7.5 x 10 4
0.2 = 2/10 = 2 x 10-1 =
4,200,000 = 4.2 x
106
Units of Distance
Astronomical Unit (A.U.) = The average
distance Earth is from the sun. (know)
1 A.U. = 149,597,900,000 meters
So, 1AU ~ 1.5 x 1011 m ~ 1011 meters
Light-year (ly) = the distance light travels in
one year of time. (know)
• Speed of light = 3.0 x 108 meters per second
1 ly = 9.5 x 1015 meters ~ 1016 meters
1 ly = 63,000 A.U. (know)
Units of
Distance
Order of Magnitude
Two values are of the same order of magnitude
if they are approximately equal (to within one
factor of 10).
Same order of magnitude?
1400 and 900? YES
1 A.U. and 25 A.U.? no
5.5 x106 and 1.2 x 105? no
8000 mi and 14000 mi? YES
(8x103 mi and 14x103 mi)
The Grand Tour
Smaller
• Planets
(107 m)
• Stars
(109 m)
• Star Clusters
(1011m)
• Galaxies
(1020m)
• Galaxy clusters
(1021m)
• Superclusters
(1024m)
• Observable Universe (1026m)
Larger
(Don’t memorize!)
Units
of
Distance
1020
1026
1015
1010
105
10-5
Orders of Magnitude
10-10
10-15
Distances You Need to Know
The diameter of:
Earth is about 4 times that of the Moon.
Jupiter is about 10 times that of the Earth.
the Sun is about 10 times that of Jupiter.
The distance to the Sun is about 100 times
the diameter of the Sun.
DEARTH
DJUPITER
DSUN
1 AU
Pluto’s orbit
= 4 Dmoon
= 10 DEARTH
= 10 DJUPITER
= 100 DSUN
= 40 AU from the Sun (~size of our solar system)
What Science is NOT
Philosophy
Cultural Beliefs
Religion
Personal
Conditional
Emotional
Word usage:
Theory – the fundamental principles
underlying a science, art … such
as music theory, germ theory, or
theory of equations or gravity.
Theory does not convey
uncertainty. (The correct word
involving uncertainty
is
hypotheses.)
The Scientific Method
“Real”
World
Initial Observations
(Assumptions)
Model
(hypothesis)
Compare to
Predictions (Test)
Observe or Experiment
 theorize/model
 predict
 test
 modify
Revise model to
match observations
or experiments
The Scientific Method
Construct Hypothesis, then
Conduct Experiment to Test it!
Science progresses in a self-correcting
manner. No significantly erroneous
Initial Observations conclusion or false hypothesis can be
(Assumptions)
sustained for long as new observations
will knock down incorrect ideas. Takes
time!
Leads to Theory!
“Real”
World
Model
(hypothesis)
Compare to
Predictions (Test)
Revise model to
match observations
or experiments
The Scientific Method
1. Why is Astronomy different that any other science in
the way in which the scientific method is applied
(especially when dealing with stars and galaxies)?
In most cases, there is no way to perform an
experiment, astronomers can only make
observations. Observe
 theorize/develop model
 use model to predict
 test model through observation
 modify
2. Why is this a valid statement? Theories can
be proven FALSE, but never completely true!
Equal Theories?
Two Equal theories
- explain all the observations equally well
- explain all the experiments equally well
Which is preferred? The simplest one is probably correct!
Use the Principle of Parsimony (or Occam’s razor-William of Ockham)
- the one with the fewest assumptions (know)
Eastern Summer Sky
Eastern Winter Sky
Constellations
Constellations – groups of
stars named by ancient
cultures to honor gods,
animals, legends, etc.
• 88 (official) total number
• 12 on the zodiac historically
13 on the zodiac today!
• Patterns come from star
positions ONLY
Orion Star Field
Constellations
Constellations – groups of
stars named by ancient
cultures to honor gods,
animals, legends, etc.
• 88 (official) total number
• 13 on the zodiac
• Patterns come from star
positions ONLY
Constellation boundaries
Constellations – groups of
stars named by ancient
cultures to honor gods,
animals, legends, etc.
• 88 (official) total number
• 13 on the zodiac today
• Patterns come from star
positions ONLY
• Today a constellation is a
region in the sky that is
named for an ancient
constellation it contains.
Constellations
Constellations - Groups of bright stars close together that ancient astronomers
named after mythological characters. There are 88 official constellations today.
Zodiac - The “12” constellations through which the Sun seems to pass as it moves
in its yearly path along the ecliptic. Today the zodiac consists of 13 constellations!
The 12
classical
zodiacal
constellations
Ophiuchus
The Ecliptic Plane
Ecliptic – path of the
Sun in the sky OR the
Earth-Sun plane
Ecliptic – the apparent path of
the Sun through the “fixed”
stars over the course of a year.
Long Term Changes - Precession
wobble
Precession
The Earth “wobbles” as it rotates, much like a top.
It takes 26,000 years for the Earth to complete one “wobble”.
As a result, Polaris will not always be the North Star.
As a result, your “sign” is changing.
Your Real “Sign” Today
• 13 Astronomical Constellations of the Zodiac
• Constellation
Dates
Capricornus
January 19 to February 15
Aquarius
February 16 to March 11
Pisces
March 12 to April 18
Aries
April 19
to May
13
Taurus
May
14 to June
19
Gemini
June
20
to July
20
Cancer
July
21
to August
9
Leo
August 10 to September 15
Virgo
September 16 to October 30
Libra
October 31 to November 22
Scorpius
November 23 to November 29
Ophiuchus
November 30 to December 17
Sagittarius
December 18 to January 18
Observations of the Sky
•
•
•
•
•
Is the Earth flat?
Why do the stars move/change?
What causes the seasons?
What causes eclipses?
Why does the Moon have phases?
Star Trails
The Round Earth
Observations
Solar
Eclipse
Other celestial bodies
Eclipses
Disappearing ships
Stars disappear as you change position
Lunar
Eclipse
Other celestial objects
are round!
Earth’s shadow on the
Moon is curved during a
Lunar eclipse.
Motion of the stars
Where on Earth is the observer?
North Pole
Equator
The Celestial Sphere
• Equator
• North Pole
• South Pole
Definitions:
Horizon: The plane tangent to the earth’s surface at the
observer’s location.
Altitude: An object’s angle above the horizon.
Latitude: The altitude of the north star (Polaris) at
your location. The north star is always
directly above the north pole.
Zenith:
The point directly above you.
90
The latitude of the north pole is ________
degrees.
0
The latitude of the equator is __________
degrees.
The Celestial Sphere
•
•
•
•
•
•
•
Equator
North Pole
South Pole
Horizon
Zenith
Altitude
Latitude
Equinoxes – Sun crosses the celestial equator (twice a
year) Spring and Fall. (Spring = Vernal)
Solstices – Sun’s farthest northerly or southerly position
(Summer or Winter)
With respect to the →
Northern Hemisphere
Equinox – Sun crosses
the celestial equator
(Spring and Fall)
Solstice – Sun’s farthest
northerly or southerly
position (Summer or
Winter)
(For the Northern Hemisphere)
Locating objects in the sky
Geographers use Longitude and Latitude to
specify locations on Earth. Astronomers
specify the location of objects in the sky
using the celestial coordinates of
Right Ascension and Declination.
Right Ascension: (RA) is measured in
angular units of hours, minutes and seconds
and increases in the eastward direction.
Zero right ascension is usually chosen to be
the position of the Sun in the sky at the
instant of the vernal equinox.
Declination: (dec) is measured in degrees
north or south of the celestial equator. The
celestial equator is at dec=0°, while the
north celestial pole resides at dec=90°.
•
•
Motions of the Sun
Sun Cycles
Diurnal – Rotation, Earth spinning, length of a day
Annual – Revolution, Earth orbit, length of a year
Meridian – North-South line
dividing the sky equally
Ecliptic – path of the Sun in the
sky OR Earth-Sun plane
Motions of the Earth
At the equator, an object is moving 1000 mph due to Earth’s
rotation! Earth orbits the Sun at 66,000 mph!
• Diurnal – Rotation, Earth spinning (East), length of
a day
•
Annual – Revolution, Earth’s orbit (East), length of
a year
Meridian – North-South line dividing the sky equally
Ecliptic – path of the Sun in the sky or Earth-Sun plane
The earth revolves 360º Eastwardly around the Sun in one
year (365.24 days) or 360/365.24  1º per day.
Solar and Sidereal Days
Solar day – time measured by
the Sun’s position
Sidereal day – time measured
by the position of the stars
to the stars
Solar and Sidereal Days
Sidereal day – time by the stars
The earth rotates 360º in one
sidereal day of 23hr. 56 min.
Solar day – time by the sun
The earth rotates 361º in one
solar day of 24hr.
The time of day for the
man is noon in both
instances.
to the stars
The Seasons
Factors that cause the seasons? Closer to Sun in Summer?
The Seasons
The earth is actually closest to the sun in December and
farthest from the sun in July (but not by much).
The Seasons
So, what are the factors that cause the seasons?
The Seasons
Seasons - caused by 23.5° tilt of Earth’s
axis of rotation with respect to the
ecliptic.
Distance Important? Yes or
No
Reasons for Warm Days
1. Sun is above the horizon longer in the summer
2. More direct light in the summer
- Direct sunlight produces more heat than indirect light
The
Celestial
Sphere
• Equator
• North Pole
• South Pole
With a point of light
and no other
information, you
cannot tell how far
away it is.
(Consider driving
at night.)
So, how do we
determine distance?
Measuring using
Angles
• 360 in a circle
• 1 = 60 arcminutes
= 60’
• 1’ = 60 arcseconds
= 60”
Measuring using
Angles
• 360 in a circle
• 1 = 60 arcminutes
= 60’
• 1’ = 60 arcseconds
= 60”
So there are 3600
? .
arcseconds in 1.
(Index finger~1˚)
(Fist at arms length~10˚)
Math Notation
The symbol  means:
“is proportional to”.
When dropping an object to the ground, its final speed v is
proportional to the initial height h. (As h goes up, v goes up)
v h
When examining your bank account, the amount of money in
savings is inversely proportional to how much you are spending.
(As spending goes up, your savings goes down)
savings 
1 _
buying
Angular Size, True Size, and Distance
Angle #1
Angle #1
True
Size
True
Size
Angle #2
Distance
Without knowing distance, the man cannot tell the difference
between the size of the red and blue objects. What happens if the
red object moves closer? The angular size of the red object increases.
The Measurement of Distance
Angular Size, True Size, and Distance
True Size
Angular size  Distance
Angle #1
Angle #1
Angle #2
Distance
True
Size
True
Size
Angular Size, True Size, and Distance
Angle #1
Angle #1
Angle #2
Distance
Angular size  True Size
Distance
True size  Angular Size
Distance  Angular Size
True
Size
True
Size
Angular Size, True Size, and Distance
Distance
Angular size  True Size
Distance
increases
As the True size increases, the Angular size __________
For a given object,
As the Distance increases, the Angular size __________
decreases
Angular Size, and Distance
(Distance, D = R, Radius of Circle)
θ = Angular Size
Baseline
q

Circumfere nce 360 
(C=2πR=2πD)
Baseline
q

2 (Distance) 360
D=?
Baseline
q
D=?
This assumes that the Baseline is short
compared to D so Baseline is close to the
curved distance between observations.
360 Baseline
Distance
2
q
Distance  57.3 
Baseline
q
Putting it to numbers. What is the size of the moon?
θ = angular size
q
Distance  57.3 
Baseline
q
Distance=57.3° x (True Size/θ)
so Size = Distance x (θ/57.3°)
Size = Moon’s (radar) Distance x (angular size /57.3°)
q = 0.517° (about 1/2 the size of you little finger at arms length)
Size = 385,000km x (0.517°/57.3°) = 3474 km
Parallax
– the apparent change in position of
an object due to the change in the
location of the observer.
Observer A
Observer B
Why?
Stellar Parallax
Earth
1
Sun
2
Earth
Orbit
Parallax - apparent motion of a foreground object with respect
to the background as the location of the observer changes.
Star Parallax
The “nearby” object’s
apparent displacement,
or shift, relative to the
more distant stars.
Prologue
Makeup of the Universe
Scientific Notation (Appendix 1)
Units of Distance and Astronomical
Measurement (Appendix 2)
•
Astronomical Unit (A.U.)
average Sun/Earth Distance
•
Light year (LY) = 63,000 AU
•
Parsec = 3.26 LY
•
Speed of Light c=3x108m/s
=3x105km/s
Motion of the Sun
Earth’s Motions
- rotation
- revolution
The Seasons
Angle, size, distance relation
Parallax
Look through tables p A-3 to A-6.
Prologue-Exploring the Heavens (p 2-21)
The Scientific Method
Constellations
Celestial Sphere
- Angles
- Celestial Poles, Equator
- Zenith
- Latitude
Read through answers to
Concept Check Questions and
Self-Test Questions (p AK-1 to AK-5)
No problems involving math will be
given on tests.
(wait)
What Time is it?
12:00 am (midnight)
It’s time to play …
Thanks
Playing!
What
timefor
is that
couple
Earth
getting married?
Eastward
6 am
6 pm
12:00 pm (noon)
```