Image PowerPoint
Chapter 1
Last revised:
25-Jan-10
Astronomy Today,
5 th edition
Chaisson
McMillan
© 2005 Pearson Prentice Hall
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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
Orion’s Belt
Orion Nebula (M42)
Rigel
The Orion
Constellation
One of 88 in the sky

• Greek letters
• Scientific notation (powers of 10)
• SI Units (mks system)
• Fundamental constants
• Periodic Table of the Elements
• Atomic & molecular structure

Numbers are written in form of a x 10 b
Ordinary decimal notation
300
4,000
5,720,000,000
−0.0000000061
Scientific notation
(normalized)
3 ×10 2
4 ×10 3
5.72
×10 9
−6.1×10 −9

•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/s 2 ; force in kgm/s 2 (= 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:
Quantity speed of light in vacuum
Newtonian constant of gravitation
Symbol c
G
Planck constant h proton mass m p
Value
Relative Standard
Uncertainty
299 792 458 m·s −1 defined
6.67428(67) ×10 −11 m 3 ·kg −1 ·s −2
1.0 × 10 −4
6.626 068 96(33) ×
10
−34 J·s
1.672 621 637(83)
× 10 −27 kg
5.0 × 10 −8
5.0 × 10 −8

PERIODIC TABLE OF THE ELEMENTS
Atomic Number (Z)
= #protons = #electrons
Atomic Weight /Mass Number
(#protons + #neutrons)

Helium
Z = 2
Beryllium
Z = 4
ATOMIC & MOLECULAR STRUCTURE
Lithium
Z = 3
Methanol
CH
3
OH
Methane
CH
4
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 are
About the size of the Earth!
sunspots

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

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 are now defined by the IAU as 88 areas of the sky. They usually contain the old star groups from earlier times.

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

To the ancients all stars were equidistant on the celestial sphere
Figure 1-9
Orion in 3-D
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.

Summer Sky
Figure 1-14
Typical Night Sky
Winter Sky

Figure 1-15
The Zodiac Constellations
WINTER
SPRING
SUMMER
FALL
Ecliptic

Solar and
( Relative to the Sun - the Sun overhead)
Sidereal Days ( Relative to the stars - 360 degree rotation )
Solar day takes 4 minutes more to get Sun overhead

Toward a distant star
Solar and Sidereal Months

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

Moon is farther from Earth due to its elliptical orbit and therefore does not cover the Sun’s disk
Figure 1-26
Annular Solar Eclipse
Earth
Total Annular Partial

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
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
Line of Nodes

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
* d
*
= 1 arcsecond
= 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)
0 h 0 m 0 s to 24 h
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.

• 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!