Transcript Ch. 1 - University of Tennessee Department of Physics and Astronomy

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Chapter 1
Astronomy Today,
5th edition
Last revised:
25-Jan-10
Chaisson
McMillan
© 2005 Pearson Prentice Hall
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Learning Goals for this Chapter
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What is the scientific method?
Scientific notation, units and prefixes
The celestial sphere & angular measurement
Motion of the Sun, Moon & stars in the sky
Phases of the Moon
Precession of the Earth’s axis
The sky clock & calendar – archaeoastronomy
Lunar and solar eclipses
Parallax measurements for distances and sizes
Chapter 1 Opener
Charting the Heavens: The Foundations of Astronomy
Betelgeuse
-Orionis
58 Orionis
The Orion
Constellation
Orion’s Belt
Orion Nebula (M42)
Rigel
One of 88 in
the sky
Sizes/Scales in the Universe
Units and Scales
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Greek letters
Scientific notation (powers of 10)
SI Units (mks system)
Fundamental constants
Periodic Table of the Elements
Atomic & molecular structure
Greek Alphabet
Scientific Notation
Numbers are written in form of
a x 10b
Ordinary decimal
notation
Scientific notation
(normalized)
300
3×102
4,000
4×103
5,720,000,000
5.72×109
−0.0000000061
−6.1×10−9
SI UNITS
•Measurement system used all over the world
except for 3 countries (US, Liberia & Burma)
• Base units are the meter(m), kilogram(kg) & second(s)
for length, mass & time
• Other units made by combining these,
e.g., velocity in m/s;
acceleration in m/s2;
force in kgm/s2 (= Newton) ;
energy in N·m (= Joule);
power in J/s (= Watt)
Fundamental Constants
Physical quantities that are generally believed to be both
universal in nature and constant in time.
Examples:
Relative Standard
Uncertainty
Quantity
Symbol
Value
speed of light in
vacuum
c
299 792 458 m·s−1 defined
Newtonian
constant of
gravitation
G
6.67428(67)×10−11
m3·kg−1·s−2
Planck constant
h
6.626 068 96(33) ×
5.0 × 10−8
−34
10 J·s
proton mass
mp
1.672 621 637(83)
× 10−27 kg
1.0 × 10−4
5.0 × 10−8
PERIODIC TABLE OF THE ELEMENTS
Atomic Number (Z)
= #protons = #electrons
Atomic Weight /Mass Number
(#protons + #neutrons)
ATOMIC & MOLECULAR STRUCTURE
Helium
Z=2
Lithium
Z=3
Beryllium
Z=4
Methane
CH4
Methanol
CH3OH
Caffeine
Figure 1-1 Earth
= 15,000 x (3/5)mi/km =9000 mi
Figure 1-2 The Sun
X (3/5)mi/km = 900,000 mi
sunspots
Sunspots are
About the size
of the Earth!
Figure 1-3 Spiral Galaxy (similar to our Milky Way)
Latest News:
Milky way thickness
was thought to be 6000 ly.
Now seems to be 12,000 ly.
Figure 1-4 Galaxy Cluster
(1 ly = 6 trillion miles)
Figure 1-5
Sizes and
Scales
Figure 1-6 Scientific Method
The Scientific Method
The
Traditional
Scientific
Method
Figure 1-7
A Lunar Eclipse
The Moon traveling through the shadow of the Earth
Figure 1-8
Constellation Orion
Naked eye view of bright stars
In Orion
Traditional stick figure constellation
Constellations
Constellations are now
defined by the IAU as 88
areas of the sky. They
usually contain the old
star groups from earlier
times.
Asterisms vs.
Constellations
Asterism - Easily
recognizable pattern of
stars.
Can be within a
constellation
(e.g., Big Dipper in
Ursa Major)
OR
From more than one
constellation
(e.g., Summer Triangle
– one star each from
Lyra, Cygnus and
Aquila)
Centaurus
Figure 1-9
Orion in 3-D
To the ancients all stars
were equidistant on
the celestial sphere
Once we could determine stellar
distances then we found stars at
Varied distances and moving in
many directions
Figure 1-10
Constellations Near Orion
Figure 1-11
TheCelestial Sphere
Figure 1-12
Northern Sky
Seasons
Caused by the 23½° tilt of Earth’s rotational axis to the
ecliptic plane
Ecliptic -The Apparent Path the Sun takes across the Sky
Fall
Equinox
Spring
Equinox
Motion of Objects in Sky
Relative to the Horizon
Seasonal
Movement of Sun
in the Sky
Seasonal
Length of Days
Seasonal
Movement of
Sunrise
and
Sunset Positions
Picture of solar paths over the course of one year
showing the change in sunrise/sunset positions on the horizon
and the height of the Sun above the horizon at noon
Some of the preserved examples of the
thousands of examples of historic
structures constructed by many civilizations
to follow the motions of the Sun, Moon and stars
in order to keep time.
Figure 1-14
Typical Night Sky
Summer Sky
Winter Sky
Figure 1-15
The Zodiac Constellations
WINTER
SPRING
SUMMER
Ecliptic
FALL
Solar
(Relative to the Sun - the Sun overhead)
and
Sidereal Days
(Relative to the stars - 360 degree rotation )
Solar day takes 4 minutes
more to get Sun overhead
Solar and Sidereal Months
Toward a
distant star
Figure 1-19
Variations in the Solar Day
Time Zones
Figure 1-18
Precession:
the path of the north
celestial pole in the sky
Period of 26,000 yrs
Presently the “North
Star” is Polaris
In ancient Egypt the
North star was Thuban
In the distant future
the North star will be
Vega
Figure 1-21
Lunar Phases
Lunar Phases
Rising &
Settting Times
Lunar Eclipse
Earth’s shadow
Figure 1-24
Total Solar Eclipse
Solar Corona
Eclipse Paths
Figure 1-28
Eclipse Tracks
Figure 1-25
Types of
Solar
Eclipses:
Partial,
Total
&
Annular
Umbral
shadow
Figure 1-26
Moon is farther
from Earth due to its
elliptical orbit and
therefore does not
cover the Sun’s disk
Earth
Total Annular Partial
Annular Solar Eclipse
How can we explain why eclipses
are seen so rarely by most of us
living here on Earth.
Why aren’t they seen every month of
the year?
Intersection of the ecliptic and lunar orbital planes
Figure 1-27
Eclipse
Geometry
Lunar orbital plane is
tilted 5 degrees from the
ecliptic plane
Line of Nodes
Only when the
Line of Nodes
points towards the Sun
can the Moon, Sun & Earth
be on that line together
and cause eclipses
to occur
More Precisely 1-1
Angular
Measurement
Units
Figure 1-32
Parallax
Geometry
Figure 1-29
Triangulation
Parallax
Method
of
determining
distances
The Surveyor’s
Method
Figure 1-30
Geometric Scaling
More Precisely 1-3a
Measuring Distances with Geometry
More Precisely 1-3b
Measuring Diameters with Geometry
Stellar Parallax
d* = 1/θ*
Examples:
θ* = 1 arcsecond (˝ )
d* = 1/1 arcsec
= 1 parallax arcsecond
[parsec or pc]
θ * = 0.002”
d* = 1/0.002” = 1/(2.0x10-3)˝
= 0.5 x 10+3 pc = 500 pc
= 500 (3.26 ly) ≈ 1600 ly
This was first able to be done in 1838
by Friedrich Bessel when telescopes
got good enough to see these very
tiny angular movements of arcseconds.
People in the past thought the Earth was flat.
NO! They were sailors and they watched lunar
eclipses. Both of these experiences told them
the Earth was a spheroid.
Ships sailed over the horizon appearing to
disappear hull first and then the sails They
reappeared in the opposite order.
The Earth’s shadow on the Moon appears as a
circle.
Figure 1-33
Eratosthenes’ Method of
Measuring Earth’s Radius
About 200 BC
More Precisely 1-2
Celestial Coordinates
Declination (δ)
90°N to 90°S
Right Ascension (RA)
0h0m0s to 24h
0 RA starts at the spring
equinox pt. on the celestial
sphere. This pt. moves
due to precession so
coordinates need to be
recalculated for different
“epochs”. At present that
pt. is in Aries and we use
Epoch 2000 or 2050 star
charts.
Stellar Catalogs
• The following 3 slides show typical star
catalog lists for the nearest stars to the
Earth and the brightest stars seen from
Earth
• Note the columns of stellar properties such
as their coordinates (RA & Declination)
and their parallax/distances
25 BRIGHTEST
STARS
R.A.
Decl.
App.
Mag.
d*
Spectral
class
Abs.
Mag.
Nearest Stars
Nearest Stars (again)
Most stars come in multiples!