Review for Astronomy Exam 1
• Note that a Review
emphasizes the main
concepts and is not to
replace your e-text and
notes in class.
• Do not expect a review to
cover everything or include
much on critical thinking.
edited by Michael J. Ruiz for website posting
prepared
by
Lyubov Nichols
1 mm = 0.001 m = 10-3 m
1 cm = 10 mm = 0.01m = 10-2 m
1 m = 100 cm = 1000 mm
1 km = 1000 m =105 cm
1 m = 3.28 ft
1Ȧ = 0.1 nm
1 nm = 10 Ȧ
1 pc = 3.3 ly
100 cm = 1000 mm = 103 mm
100 m = 100,000 mm = 105mm
6560 Ȧ = 656 nm
410 nm = 4100 Ȧ
100 pc = 330 ly
Quark: 10-16 m
Quasar: 1026 m away
Sense of Scale
• Solar System –
80 AU across
• Our Galaxy 100,000 ly across
• Earth – Star (Proxima Centauri, 4 ly)
3 ly away (approx.)
• Andromeda Galaxy (2.5 Mly)
3 million ly (approx.)
• Local Group of Galaxies –
10 million ly across
• Quasars –
10 billion ly away
From Quark to Quasar there is 42 (16 + 26 ) powers of ten in distance
16
26
Quark ----------------- Arm (1 m) ----------------- The reaches of the Universe
Sun
-27
Moon -13
Venus - 4
Sirius -1.5
You can see 2000 stars with the naked eye.
The faintest star
+ 25
Magnitude vs Luminosity (intensity)
Hipparchus:
1
2
3
4
5
6
m
Weber-Fechner law:
2.5 x 2.5 x 2.5 x 2.5 x 2.5
L
6.25 x
6.25
x 2.5
40
x 2.5 = 100
A star 6 times more intense than +5 mag star will have mag ____
A star 2 mag dimmer in brightness will be measured __________
A star 15 times less intense will be measured ________________
A star 40 times less intense than -10 mag star will have mag ____
The standard distance for Absolute Magnitude is 10 pc = 33 ly
Precession
13,000yr
(Ursa Minor)
26,000 yr
(Lyra)
Cosmic “Clock”
Cosmic “Day” is 26,000 yr.;
Cosmic “Hour” is 2000 yr.
Polaris
North Celestial Pole is drifting toward Polaris
The Vernal Equinox is leaving Pisces
to enter the “Age of Aquarius”.
“Age “ changes every 2000 years
( 26,000/12 = 2150 yr)
(26000/13 = 2000 yr)
Vega
Greek Ancient Astronomers
Thales:
the Universe is made of Water
Heraclitus: the Universe is made of Fire
Empedocles: the Universe is made of Water, Air, Fire, Earth
Aristotle:
the Universe has 8 crystalline spheres
(Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn, Stars)
he added a fifth element “quintessence” to his
cosmological system
Ptolemaic model of the Universe:
the epicycle, a little circle that the planet follows
as it proceeds around the Earth on a larger circle.
Eratosthenes: Earth was discovered to be round.
130 CE
Bright stars are usually designated by a Greek letter: α, β, γ, δ, ...
(α Lyrae in Lyra is Vega)
Arab Astronomers
• Alhazen (1000 CE)
• Arab astronomers named the stars.
• Egyptian divided the sky into regions called
constellations.
Anasazi Sun Dagger (New Mexico)
Stonehenge in England
Bighorn Medicine Wheel
THE BIG FIVE
Copernicus
Heliocentric model of
the Universe
● First Observatory
Tycho Brahe ● Tycho’s Supernovae (1572)
● 30 Years of Observations
Galileo Galilei
● Laws of Terrestrial Motion
● Moons of Jupiter
● Rings of Saturn
● Phases of Venus
● Craters on the Moon
● Sunspots
KEPLER’S LAWS of Planetary Motion
• Law of Ellipses - The planets orbit the Sun in
elliptical orbits with the Sun at one focus.
• Law of Areas - A line drawn from a planet to the Sun
sweeps out equal areas in equal times.
• Law of Periods - T x T = R x R x R
Planets far from the Sun
T2 = R3
take longer to orbit the Sun
The planet's year depends on the distance from the Sun.
Voyager 1 (1977)
T2 = R3
R = (5+1)/2 = 3 AU
T = √ R3 = √3 x 3 x 3 =
= √27 ≈ √25 = 5 yr
Tvoyager = 5 yr / 2 = 2.5 yr
at R = 4 AU
at
R = 3 AU
T = √R3 = √ (4x4x4 )= √ 64 = 8 yr
T = √R3 = √(3x3x3) = √ 27 ≈ √25 = 5yr
Isaac Newton
Laws of Motion
I. A body experiencing no force continues at rest or at constant speed
in a line.
ɑ = F/m
II. F = mɑ
A small mass will undergo a greater
change in motion than a larger mass.
III. Action – Reaction
Universal Law of Gravitation
Inverse Square Law
F ~ 1/r2
r = 9 AU F = 100 N 3 times less,
at r = 3 AU F = ?
F = 100 x (3)2 = 900 N
r = 20 AU F = 100 N 2 times more
If at
at
at
F=?
F = 100 / (2)2 = 25 N
at r = 15 AU F = 100N
5 times less
at r = 3 AU F = ?
F = 100 x (5)2 = 2500 N
r = 40 AU
New Moon, Spring Tides
Spring Tides , the greatest tides
Third Quarter, Neap Tides
Neap Tides, the least tides
Lunar Eclipse:
A total duration is 5-6 hr.
If the size of the Sun increases
the umbra decreases.
If you were to move Sun farther from planet, the umbra increases.
..................... move Sun closer to planet, the umbra decreases.
Solar Eclipse:
A total duration is 2 hr.
The annual solar eclipse when …
270 km
Typical duration is 2-3 min.
Maximum duration is 7.5 min
The Sun moves about one degree from west to east with respect to the 'fixed' stars.
Tsol = 24 hr
10=4min
Tsid= 23 hr 56min
The Solar Day is the time it takes the Earth to
rotate once with respect to the Sun
The Sidereal Day is the time it takes
the Earth to rotate once
with respect to the fixed stars.
Sidereal Day is 4 minutes shorter than Solar Day
(1/360) x 24 h x (60 min/h) = 4 min
360 days ……. 4min
180 days ……. 8 min
90 days ………16 min
60 days ……… 24 min
30 days ……… 48 min
23.50
The Earth's equator is tilted 23.50 from the vertical.
North Pole +900N
Canada +450N
Equator, 00
N
Tropic of Cancer
Tropic of Capricorn
S
Vernal Equinox
Spring
Mar 21
Aphelion (1.02 AU)
Winter
Perihelion (0.98 AU)
Summer Solstice
Jun 21
Winter Solstice
Dec 21
Summer
Autumn
Autumnal Equinox
Sep 21
The tilt of axis determines the seasons!
Which parts of the world could these be?
Dec. = +450
Dec. = 0
Dec. = +900
Canada
Philadelphia
Equator
North Pole
Time Zones
3600
= 24h
3600 / 24 = 150
UT - 5 hr = EST (Asheville)
8 UT – 5 hr = 3 a.m.
150 =1h
UT - 4 hr = EDT (Asheville)
21 UT – 4 hr = 5 p.m.
Distance from lens to F = f.
Image stays real, inverted, and gets larger for object distances > f.
Image stays real, inverted, and gets smaller for distances > f.
What happens when the object is at 2f, i.e., twice the focal distance from the lens?
Image stays virtual, upright, and gets
smaller for object distances less than f.
Image stays virtual, upright, and gets larger
for object distances less than f.
.
400nm
450 nm
shorter wavelength (λ)
higher frequency (f)
greater energy (E)
500 nm
550 nm
E210 nm
>
600 nm
650 nm
E410 nm
E410 nm > E656 nm
Electromagnetic radiation is energy composed of rapidly
varying electric and magnetic fields. speed c = 300,000 km/s
700 nm
longer λ
lower f
lower E
The Theory of Special Relativity (1905):
● The Laws of Physics are the same in all Inertial Frames
● The Speed of Light is the same in all Inertial Frames
c = 300,000 km/s ( uniform motion cannot be detected)
Albert Einstein
E = mc2
m = E/C2 = (1017 J)/(300,000,000 m/s)2 ~ (1017 J)/(1017 m/s) = 1 kg
~ means approximately
One megaton of TNT is equivalent to the energy released from 1kg.
ɑ = 9.8 m/s2
General Theory of Relativity (1915)
Gravity is the result of the curved fabric of the spacetime.
↑
The principle of equivalence is
the foundation of general relativity.