PHY 1306

 

STELLAR AND GALACTIC

ASTRONOMY

 

DR. PINSKY

406G S&R

 

INTRODUCTION

 

AN INVENTORY OF

THE UNIVERSE

 

The Big Questions

* Where did our Universe come from?

 

* When did it begin?

 

* What is OUT THERE? (How big is it? Does it END?)

 

* What is the STRUCTURE of our Universe?

 

* What can we say about out (Universe's) FUTURE?

 

* Might there be places that are not in our Universe?

 

* Is time itself forever, or might it have a beginning and an end?

 

Ancient Cosmologies...(Religions...)...Ours

FIRST:

 

* Our species and its most immediate ancestors date back on the order of 2 million years (2 x 106 yrs). We know only about a very limited recent past as recorded history.

 

* Our planet is actually ~4.5 billion years old (4.5 x 109 yrs). This has been reliably known only for about the last 50 years.

 

* Our universe is on the order of 15 billion years old (15 x 109 yrs). This is only imprecisely known even now. The present limits currently range from 10 to 20 billion years.

 

* It appears that it formed in a very hot dense initial state from which it expanded (exploded) to its present form. Our present knowledge of physics can take us back to about 10-45 seconds after THE BEGINNNING. From that point to the present time, we think we are close to understanding things very well. This is the so called BIG BANG model.

Sumarians (4500-3000 BC)

* The opening of recorded histroy.

 

* In Mesopotamia (Iraq today).

 

* Subject to a chaotic existence due to varying weather (storms and floods) and the lack of natural defensive barriers. The origins of Astrology formed from a desire to make sense out of chaos. Kings were human and not gods.

 

* Earliest cosmological ideas contained in the Gilgamesh epic. Heaven and earth were once united, and were seperated to the control of the gods Anu and Enlil respectively.

 

* The Sumarians also originated the affectation with 6's that remain in our cultrue today (60 sec/min, 60 min/hr, 360 ).

 

* The Sumarians ideas were adopted and refined by the Babylonians.

 

Babylonian (3000 BC)

* Details of creation included in the Enuma Elish epic.

- The origin of the world see as a conflict of forces in the primeval chaso.

- Gods represent the personifiction of the entity they represent. For example Enki (the God of Earth) was Earth- God, the Earth itself.

 

- The present world resulted from a conflict between (the Gods of) fresh and salt water creating silt (2 Gods), which in turn give birth to the land and sky. Other aspects of nature were associated with other gods. A final conflict resulted in one of the gods of chaos being killed and having her body sliced in half to be supported in the sky by the wind and storms, becoming heaven.

* The Babylonians refined the Sumarian ideas and gave us 24 hr/day, 7days/wk, and 12 lunar months/yr. They gave us Algebra and Fractions and used the wheel and axle.

 

Judeo-Christian-Islam

(Old Testament-Genesis)

* The pinnacle of the early Sumarian and Babylonian myths.

* Originally some residue of the earlier polytheism.

* Incorporates the 7-days and the great flood from earlier mythes. Adam & Eve as well as the Garden of Eden are also taken from earlier myths. (A common general theme in many disparate religions).

Egyptian (4000 B.C. - 350 B.C.)

* Blessed with great regularity in the Nile flooding and protected by the vast surrounding deserts (and the sea to the north) Egypt developed in a calm, predictable, non-chaotic world. Pharoes were gods.

 

* The earth was a flat disc surrounded by mountainous rem (or sometimes just 4 mountains) which supported the sky (a goddess named Nut whose body is the "vault of the Heavens" and the stars and planets are suspended from her body as ornaments). The sun, Ra, is carried on a boat across Nut's back. The earth is floating on a primeval abyssal ocean from which all things were created by Ra.

 

* The Egyptians were good at Geometry, but poorer at Algebra than the Babylonians. They gave us the base 10 number system. Their year consisted of 36 ten-day "weeks".

 

Greek Astronomers

* Thales (640-546 B.C. Miletus)

 

* Anaximander (611-547 B.C. Thales' student)

 

* Pythagoras (580-500 B.C. Samos -> Crotona)

 

* Leucippus (435-? Miletus) & Democritus (460- 362 B.C. Abdera)

 

* Eudoxus (408-353 B.C. Athens)

 

* Aristarchus (310-230 B.C. Samos)

 

* Eratosthenes (276-195 B.C. Alexandria)

 

* Hipparchus (160-127 B.C. Rhodes)

 

* Ptolomy (~100 A.D. Alexandria)

Greek Astronomers

 

* Thales (640-546 B.C. Miletus)

- introduced Mathematical and Astronomical Science to Greece.

- First of the Great Wise Men.

- introduced the concept of Objective Reality to western thought.

 

* Anaximander (611-547 B.C. Thales' student)

- First introduced the concept of the infinite Universe.

- Proposed a theory of Evolution.

 

* Pythagoras (580-500 B.C. Samos -> Crotona)

- Founded Mathematics and Philosophy as well as science as we now know them.

- Perpetuated the 7-day week.

- Many theorems in the Mathematics.

> Discovered irrational Numbers

> Axiom-Theorem-Demonstration

> Re-discovered the "Pythagorean Theorem", + many others

- Founded a "School"/ "Cult"/ "Society" whcih lasted 300 years.

 

* Leucipus (435-? Miletus) & Democritus (460-362 B.C. Abdera)

- Atomic Theory - empty space inbetween

 

* Eudoxus (408-353 B.C. Athens)

- Plato's student - Best scientist of his time

- An experimentalist - Empirical view...

- Astronomer and Mathematician

 

Greeks (continued...)

* Aristarchus (310-230 B.C. Samos)

- First person to seriously advocate a Heliocentric theory of the universe.

- Measured the Relative diameters of, and distances between the earth, moon, & sun.

 

* Eratosthenes (276-195 B.C. Alexandria)

- Measured the Earth's diameter.

 

* Hipparchus (160-127 B.C. Rhodes)

- Perhaps the Greatest Astronomer in Antiquity.

- Introduced the Stellar Magnitude scale.

- Discovered the precession of the Earth's axis of rotation.

- Measured the length of the year to within 6 minutes.

- Measured the Actual diameter of and distances to the sun and moon using Eratosthenes' measurements fo the earth.

- Developed the first detailed Star Catalog.

- Could not accept the Heliocentric theory.

 

* Ptolomy (~100 A.D. Alexandria)

- Published the Almegest whcih remained the standard reference in both Astronomy and Astrology until Copernicus.

- Developed the current techniques of Celestial Navigation.

Phys 1306 - Introduction to Astronomy

Stellar and Galactic

 

Dr. Pinsky

Powers of 10

Sometimes called "Scientific Notation"

 

1 = 100

10 = 101 0.1 = 10-1

100 = 102 0.01 = 10-2

1,000 = 103 0.001 = 10-3

10,000 = 104 0.0001 = 10-4

100,000 = 105 0.00001 = 10-5

1,000,000 = 106 0.000001 = 10-6

 

10N x 10M = 10(N+M) (e.g. 10-4 x 106 = 10(-4+6) =102)

 

(10N / 10M )= 10(N-M) (e.g. 10-4 / 106 = 10(-4-6) =10-10)

Metric System Prefixes

 

103 -> Kilo (K) [Thousands] 10-3 -> mili (m)

Kilometer (Km) milimeter (mm)

 

106 -> Mega (M) [Millions] 10-6 -> micro (m)

MegaHertz (MHz) microsecond (ms)

 

109 -> Giga (G) [Billions] 10-9 -> nano (n)

Gigaparsec (Gpc) nanosecond (ns)

 

1012 ->Tera (T) [Trillions] 10-12 -> pico (p)

TeraFLOPS (TFLOPS) picoFarad (pF)

\/

V

{Floating Point Operations Per Second (in computer-eze)}

The Big Questions...

Where did our Universe come from?

When did it begin?

What is OUT THERE? (How big is it? Does it END?)

What is the STRUCTURE of our Universe?

What can we say about our (Universe's) FUTURE?

Might there be places that are not in our Universe?

Is time itself forever, or might it have a beginning and an end?

Ancient Cosmologies...(Religions...)... Ours FIRST:

Our species and its most immeadiate ancestors date back on the order of 2 million years (2 x 106 yrs). We know only about a very limited recent past as recorded history.

 

Our planet is actually ~4.5 billion years old (4.5 x 109 yrs). This has been reliably known only for about the last 50 years.

 

Our universe is on the order of 15 billion years old (15 x 109 yrs). This is only imprecisely known even now. The present limits currently range from 10 to 20 billion years.

 

It appears that it formed in a very hot dense initial state from which it expanded (exploded) to its present form. Our present knowledge of physics can take us back to about 10-45 seconds after THE BEGINNING. From that point to the present time, we think we are close to understanding things very well. This is the so called BIG BANG model.

Sumarians (4500-3000 BC)

The opening of recorded history .

In Mesopotamia (Iraq today).

Subject to a chaotic existence due to varying weather (storms and floods) and the lack of natural defensive barriers. The origins of Astrology formed from a desire to make sense out of chaos. Kings were human and not gods

Earliest cosmological ideas contained in the Gilgamesh epic. Heaven and earth were once united, and were seperated to the control of the gods Anu and Enlil respectively.

 

The Sumarians also originated the affectation with 6's that remain in our culture today (60 sec/ min, 60 min/hr, 360∞)

 

The Sumerian ideas were adopted and refined by the Babylonians.

Babalonian (3000 BC)

Details of creation included in the Enuma Elish epic.

The origin of the world seen as a conflict of forces in the primeval chaos.

Gods represent the personification of the entity they represent. For example Enki (the God of Earth) was Earth-God, the Earth itself.

The present world resulted from a conflict between (the Gods of) fresh and salt water creating silt (2 Gods), which in turn give birth to the land and sky. Other aspects of nature were associated with other gods. A final conflict resulted in one of the gods of chaos being killed and having her body sliced in half to be supported in the sky by the wind and storms, becoming heaven.

 

The Babylonians refined the Sumarian ideas and gave us 24 hr/day, 7 days/wk, and 12 lunar months/yr. They gave us Algebra and Fractions and used the wheel & axle.

Egyptian (4000 B.C. - 350 B.C.)

Blessed with great regularity in the Nile flooding and protected by the vast surrounding deserts (and the sea to the north) Egypt developed in a calm, predictable, non-chaotic world. Pharoes were gods.

The earth was a flat disc surrounded by a mountainous rim (or sometimes just 4 mountains) which supported the sky (a goddess nammed Nut whose body is the "vault of the Heavens" and the stars and planets are suspended from her body as ornaments). The sun, Ra, is carried on a boat across Nut's back. The earth is floating on a primeval abyssal ocean from which all things were created by Ra

 

The Egyptians were good at Geometry, but poorer at Algebra than the Babylonians. They gave us the base 10 number system. Their year consisted of 36 ten-day "weeks".

Judeo-Christian-Islam (Old Testament- Genesis)

The pinnacle of the early Sumarian and Babylonian myths.

Originally some residue of the earlier poly-theism.

Incorporates the 7-days and the great flood from earlier myths. Adam & Eve as well as the Garden of Eden are also taken from earlier myths. (A common general theme in many disparate religions).

Hindu

Buddhist

Meso-American (from about 500 B.C.?)

A very sophistocated observing capability as well as complex calendars. Perhaps as significant as the Babylonian achievements, but mostly lost to us.

 

They viewed the Universe as being layered, with the moon, the clouds, the stars, the Sun, planets and ultimately the male-female creator-god occupying the thirteenth and outermost layer. Similar layers make up the under-world.

no sense of concentric structure. No center, only stacking.

Greek (650 B.C. - 150 A.D.)

The Greeks had by far the most profound influence on modern western philosophy. They laid the foundations for modern science and mathematics as well as philosophy itself.

Greek cosmology was the first to seriously attempt a quantative rather than mythological basis.

The greeks were the first to measure the diameter of the earth, moon, and sun, as well as the distances between them. They knew the shape of the earth and debated the competing choices of a sun-centered (heliocentric) vs. an earth-centered (geocentric) universe.

Greek Astronomers

Thales (640 - 546 B.C. Miletus)

Anaximander (611 - 547 B.C. Thales' student)

Pythagoras (580 - 500 B.C. Samos -> Crotona)

Leucippus (435 - ? Miletus) & Democritus (460 - 362 B.C. Abdera)

Eudoxus (408 - 353 B.C. Athens)

Aristarchus (310 - 230 B.C. Samos)

Eratosthenes (276 -195 B.C. Alexandria)

Hipparchus (160 - 127 B.C. Rhodes)

Ptolomy (~100 A.D. Alexandria)

Greek (650 B.C.-150 A.D.)

 

* The Greeks had by far the most profound influence on modern western philosophy. They laid the foundations for modern science and mathematics as well as philosophy itself.

* Greek cosmology was the first to serously attempt a quantative rather than mythological basis.

* The Greeks were the first to measure the diameter of the earth, moon and sun, as well as the distances between them. They knew the shape of the earth and debated the competing choices of a sun-centered (heliocentric) vs. an earth-centered (geocentric) universe.

 

Meso-American (from about 500 B.C.?)

* A very sophistocated observing capability as well as complex calenders. Perhaps as significant as the Babylonian achievements, but mostly lost to us.

* They viewed the Universe as being layered, with the moon, the clouds, the stars, the Sun, planets and ultimately the male-female creator-god occupying the thirteenth and outermost layer. Similar layers make up the under-world.

* No sense of concentric structure. No center, only stacking.

Powers of 10

 

* Sometimes called "Scientific Notation"

* 1=100

 

* 10=101 0.1=10-1

 

* 100=102 0.01=10-2

 

* 1,000=103 0.001=10-3

 

* 10,000=104 0.0001=10-4

 

* 100,000=105 0.00001=10-5

 

* 1,000,000=106 0.000001=10-10

* 10N x10M=10(N+M) (e.g.10-4 x106=10(-4+6)=102)

 

* (10N/10M)=10(N-M) (e.g.10-4/106=10(-4-6)=10-10)

Metric System Prefixes

 

* 103 -> Kilo (K) [Thousands] 10-3 -> mili (m)

Kilometer (Km) Milimeter (mm)

* 106 -> Mega (M) [Millions] 10-6 ->micro(m)

MegaHertz (MHz) microsecond(ms)

* 109 -> Giga (G) [Billions] 10-9 -> nano (n)

Gigaparsec (Gpc) nanosecond (ns)

* 1012 -> Tera (T) [Trillions] 10-12 -> pico(p)

Tera FLOPS (TFLOPS) picoFarad (pF)

 

* {Floating Point Operations Per Second

(in computer-eze)}

 

Johannes Kepler (1571-1630)

 

3 Laws of Planetary Motion

1. Planets move in orbits which are ellipses with the sun at one focus

 

2. The imaginary line between the sun and a planet sweeps out equal areas in equal times.

 

3. P2 = a3

 

Sidereal Semi-major axis

period of the ellipse (A.U.)

(years)

 

Page 16 is a copy of a text and illustrations (3.3 Kepler 41)

 

Newton's Laws of Motion

 

1. Inertia - Momentum = Mass x Velocity

2. Force = Mass x Acceleration

3. Action - Reaction -> Momentum conserved

 

Mass - Weight

(Force)

Universal Graviation

Force = G (Mm/R2)

Newton's First Law

(The Law of Inertia)

 

An object in motion tends to remain

in motion.

 

An object at rest tends to remain

at rest.

 

All objects possess momentum (inertia).

Momentum = Mass x Velocity

Momentum is unchange unless acted on by an outside force.

Mass -> Intrinsic Property

Weight -> Force of Gravity

Vectors -> Have Direction and Size

Scalars -> Size Only

Momentum, Velocity -> Vectors

Mass, Energy, Speed-> Scalars

Newton's Second Law

(Definition of Force)

 

A force when applied to an object produces a change in the velocity of the object-this change is called an acceleration.

The magnitude of the acceleration is given by the magnitude of the force divided by the mass.

a = F/m or F = ma

Force and acceleration are vectors!

Angular Momentum

 

Vector ("Arrow")

 

Angular Velocity

 

Angular Momentum

P = MV

L = R x P

or =(R x P)

 

Angular momentum of an isolated system is conserved!

Planetary Angular

Momentum

Ecliptic

Angular Momentum

l = mvr = pr

 

Percession

 

T Torque

(Twisting

force which

causes a

rotation)

 

F = ma

T = I

Ang. Acc.

 

Moment of Inertia

 

Gravitation

F = G (Mm/R2) = ma

Center of Mass

 

|M/(M+m)| <- M/(M+m) ->

 

GRAVITATION

 

The mutual attraction of matter for all other matter!

 

The weakest of the 4 fundamental forces is nature:

 

1. STRONG (NUCLEAR) 1

2. ELECTRO-MAGNETIC 1/137

3. WEAK (NUCLEAR) 10-6

4. GRAVITATION 10-39

F=G((m1m2)/R2)

 

NEWTON'S FORM OF

KEPLER'S THIRD LAW:

 

Again... if P is in years

and a is in AU

where m1 & m2 are in solar masses.

DERIVING KEPLER'S 3RD LAW

 

F=ma Newton's 2nd law of motion

 

F=G((mM)/r2) Newton's Law of Universal Gravitation

 

so

 

ma=G((mM)/r2)r

"unit" vector in the radial direction

 

For

Centripetal Acceleration

(Uniform Circular Motion)

 

ELECTRIC FIELD

 

All charges set up their own electric field.

 

 

VECTOR FIELD

(Magnitude & direction)

 

The strength of the field is proportional to the charge and diminishes as the square of the distance from the charge.

Other charges in the an electric field feel. A force in the direction of the field.

MAGNETIC FIELD

 

All moving charges set up a magnetic field.

 

Strength of the field is proportional to the charge times its velocity and diminishes as the distance from the ______ of motion.

 

Magnetic fields only affect moving charges, and the force exerted is at right angles to the both the ______ of motion of the effected charge and the direction of the field.

CHANGING ELECTRIC FIELDS CREATE MAGNETIC FIELDS

AND

CHANGING MAGNETIC FIELDS CREATE ELECTRIC FIELDS

 

E-Fields are at right angles to magnetic B-Fields.

Direction of Propagation

 

Transverse wave

 

ENERGY IS "________"

FLOWS IN THE DIRECTION OF PROPAGATION AT THE SPEED OF LIGHT.

 

ELECTROMAGNETIC RADIATION

(LIGHT!)

Light is nothing more than oscillation electric and magnetic fields.

These oscillations propagate from the source at the speed of light in a wave-like fashion!

Frequency (cycles per second) Hz

 

Wave Speed (C for light)

Wavelength

 

C =

WAVES

 

x f = C

Wavelength X Frequency = Speed

FOR ALL WAVE PHENOMENA

 

For light the speed is always the same (Independent

of and f ). Therefore if is known f is determined and vice versa.

This page contains two illustrations.

 

This page contains one illustration.

(The Inverse Square Law of Light Propagation)

 

ELECTROMAGNETIC

SPECTRUM

Low energy High energy

Long wavelength Short wavelength

Low frequency High frequency

LIGHT !

E = h

Energy Frequency

Planck's Constant

 

This page contains two illustrations.

(Electromagnetic Spectrum & Wavelength)

 

DISPERSION

 

The Index of Refraction is different for different wavelengths.

REFRACTION

Light moves slower in certain transparent materials than in a vacuum!

The ratio of lights speed in a vacuum to that which it has in some material is called the INDEX OF REFRACTION.

nglass = c / vglass

Refraction causes the light path to bend!

This page contains four illustrations.

 

DIFFRACTION

 

Due to interference of the waves.

 

RESOLUTION

The ability to resolve (distinguish between) two objects that are very close together!

 

The minimum angle that can be resolved is proportional to the diameter of the viewing aperture, and inversely proportional to the wavelength.

OPTICAL INSTRUMENTS

 

LENS

 

MIRROR

 

ABERRATIONS

CHROMATIC-DISPERSION

 

SPHERICAL

 

ASTIGMATISM

 

COMA

 

Three illustrations.

Four illustrations.

 

Two photos.

DOPPLER EFFECT

 

ATOMIC STRUCTURE

 

1. Atoms contain a nucleus with electrons orbiting around it!

 

2. The electrons are allowed to occupy only certain specific orbits.

 

3. Only one individual electron can be in a specific orbit at a time!

 

4. Orbits are grouped by energy.

PHOTO ABSORPTION

 

1. If a photon comes along with exactly the energy that matches the difference between two levels in an atom-it can be absorbed.

2. This absorption raises an electron between the two levels.

 

PHOTON EMISSION

 

1. If there is a vacancy in an energy level below an electron, it will drop into it emitting a photon of light.

 

2. The energy of the photon is just the difference between the two energy levels the electron moved between.

EMISSION SPECTRA

1. A hot gas will have its electrons excited to higher energy levels by collision among the atoms.

 

2. These excited electrons will then decay back down to the vacant lower levels emitting photons.

 

3. The photons will only be present with energies corresponding to the energy level differences in the atoms.

One illustration.

CONTINUOUS

EMISSION SPECTRA

ABSORPTION

 

CONTINUOUS - From hot dense objects

- All wavelengths present

EMISSION - From hot gas (Diffuse)

- Only certain specific wavelengths

ABSORPTION - From a continuous spectrum after passing through a diffuse gas

- Continuous with lines missing

Two illustrations.

RADIATION LAWS

ALL OBJECTS EMIT BLACK BODY RADIATION.

 

1. INTENSITY = T4

(STEFAN BOLTZMAN) ABSOLUTE TEMPERATURE

2. Peak intensity occurs at a wavelengths inversely proportional to abs. temp.

(WIEN LAW)

 

BLACK BODY RADIATION

 

RELATIVE

EMISSION

PER UNIT

AREA

As temperature increases...

 

1. The wavelength where the radiation is a maximum gets smaller (shorter).

2. The total amount of light emitted at all wavelengths is greater.

INTENSITY - Energy radiated (or absorbed) per unit area

 

LUMINOSITY - Total energy radiated!

 

LUMINOSITY

 

SPECTRAL LINES

 

1. NORMAL APPEARANCE

(IN LABORATORY)

2. RAPIDLY ROTATING STAR

(EFFECTS DUE TO DOPPLER SHIFT)

3. COLLISIONAL (OR PRESSURE)

BROADENING

(THE HIGHER THE PRESSURE-

THE BIGGER THE TAIL)

4. THERMAL DOPPLER

BROADENING

(THE HOTTER THE TEMP.- THE WIDER)

5. ZEEMAN SPLITTING

MAGNETIC FIELD

From a single line in the spectrum one can determine:

* Temperature -from ThermalBroadening (not very precise)

 

* Pressure -from CollisionalBroadening

 

* Rotational Velocity -from RotationalBroadening

 

* Magnetic Fields -from Zeeman Effect

 

To obtain any of the above information-you need to know only the shape of the spectral line-it does not matter where in the spectrum it occurs!

SPECTRAL LINE PROFILES

 

BROADENING MECHANISMS

1. NATURAL-Due to fundamental spread in atomic levels.

2. THERMAL DOPPLER- Due to the motion of the emitting atoms.

3. COLLISIONAL OR PRESSURE- Atoms distort one and other.

 

4. ROTATIONAL - Due to rotating source.

5. MAGNETIC (Zeeman Effect)

 

6. ELECTRIC FIELD (Stark Effect)

Similar to Zeeman

7. MOTION DOPPLER

 

FROM THE ENTIRE SPECTRUM ONE CAN DETERMINE

 

RADIAL VELOCITY

 

COMPOSITION

RELATIVE ABUNDANCE

 

TEMP.-BLACK BODY

 

One illustration.

(Exploration of the Universe, 6/E)

TRIANGULATION

PARALAX

 

DEPTH PERCEPTION

USES PARALAX

 

STELLAR PARALAX

PARSEC

(PARALAX SECOND)

Three illustrations.

 

GEOMETRIC METHODS OF MEASURING

THE DISTANCES TO STARS

ANNUAL PARALAX

 

SECULAR PARALAX

 

MOVING CLUSTERS

STELLAR MOTIONS

 

Radial Motion - The component of the space (miles/sec) motion in the direction towards or away from the sun.

 

Proper Motion -The apparent change in position (Angle/Yr.) in the sky as seen from the sun.

Space Motion - The actual true motion of the (Miles/Sec.) star with respect to the sun.

To find space motion, one needs:

 

1. RADIAL MOTION 2. PROPER MOTION 3. DISTANCE

 

ASSUME ALL 3 STARS MOVE AS SHOWN IN ONE YEAR!

 

* All 3 stars have the same Proper Motion.

* Star #1 & star #3 have the same Radial Motion.

* All 3 stars have different space motion.

 

APEX - The point which we appear to be moving towards.

 

ANTAPEX - The point which we appear to be moving away from.

STELLAR MAGNITUDES

* First introduced by Hipparchus.

 

* The smaller the magnitude the brighter the star.

 

* If 2 stars differ by 5 magnitudes, the brighter is 100 times brighter than the dimmer star.

 

OBJECT MAGNITUDE

 

SUN -26.5

 

FULL MOON -12.5

 

SIRIUS -1.5

 

NAKED EYE LIMIT +6.5

 

TELESCOPE LIMIT +24

 

SPACE SHUTTLE

TELESCOPE 30

APPARENT MAGNITUDE

 

How bright an object appears as seen from the earth.

 

ABSOLUTE MAGNITUDE

 

How bright an object would appear if it were exactly 10 parsecs away (ABS MAG = 5).

 

DISTANCE

 

Since apparent brightness varies inversely as the square of the distance-If you know the distance and the apparent magnitude you can calculate the absolute magnitude.

ALSO

 

If you know the absolute magnitude and the apparent magnitude, you can calculate the...

DISTANCE

So, if we can find a way to determine the absolute magnitude, we can find the distance.

(Since we obviously know the apparent magnitude.)

 

M - Absolute Magnitudes

m - Apparent Magnitudes

 

Luminosities

 

m1 - m2 = 2.5 log10(l2/l1)

m - M = 2.5 log10(l(10)/l(r))

 

In Parsecs

m - M = 5 log10(r/10)

 

since

(l(10)/l(r)) = (IA/102)/(IA/r2)= (r/10)2

COLOR INDEX

map - All Wavelengths

 

Magnitude ( apparent)

 

mb - Blue Mag

 

mUV - Ultra Violet Mag

 

mR - Red Mag

mb - map = Color Index

SPECTRAL TYPE

CLASSIFICATIONS

 

Purpose - To find the Temperature from the spectrum (the surface temp).

 

PROMINENT LINES

M < 3500 K RED MOLECULAR

 

K 3500-5000 K RED ORANGE NEUT. METALS

 

G 5000-6000 K YELLOW-WHITE IONIZED MET.

 

F 6000-7400 K BLUE-WHITE IONIZED MET.

 

A 7500-11000 K BLUE HYDROGEN

 

B 11000-25000 K BLUE NEUT. HELIUM

 

O > 25000 K BLUE IONIZED HELIUM

SUB-CLASSIFICATION

 

The sun is a G2 with

a surface temp. 5800 K.

This page is a copy of Table 22.1 and Figure 22.1 from

22.1 of Classification of Stellar Spectra.

 

STAR NAMES

88 - Constellations

Bayer (1603) used Greek letters.

 

Variable stars

R, S, T,... Z, RR, RS,...

then the constellation

 

This page is a copy of

Abell/Morrison/Wolff: EXPLORATION OF THE UNIVERSE, 6/E

 

This page is copy of Figure 24.2 from a page out of

The Stellar Population

 

This page is a copy of an illustration.

STELLAR NOMENCLATURE

 

1. Some of the brightest stars have ancient names (mostly Arabic).

 

Examples: SIRIUS

ALTAIR

ALDEBARAN

 

2. J. Bayer introduced the most widely used catalogue - The sky is divided into 88 constellations and the stars lettered in order of decreasing of brightness with Greek letters:

 

CENTAURI

CENTAURI

.

.

CENTAURI

.

.

 

3. Other catalogues are sometimes used

HD - Henry Draper (HD 86)

BD - Bonn Catalogue (BD 241)

etc.

TYPES OF

BINARY SYSTEMS

 

1. Optical (not a true binary) - Just two stars that appear close in the sky.

------------------------------------------------2. Visual Actually seen (both stars) if distances are known - the mass of each star can be calculated. This is the only way to directly measure the mass of a star!

(Some mass info. obtained from all binaries.)

 

3. Astrometric Only one of the stars is seen, and it shows oscillatory motion.

 

4. Spectroscopic Two sets of alternately Doppler shifting spectral lines reveal stars moving around each other.

 

5. Spectrum Two different spectral types superimposed.

 

6. Eclipsing One star passes in front of other-one direct way of measuring stellar radii.

This page is a copy of

Abell/Morrison/Wolff: EXPLORATION OF THE UNIVERSE, 6/E

"Time"

This page is a copy of

Abell/Morrison/Wolff: EXPLORATION OF THE UNIVERSE, 6/E

"Radial Velocity vs. Time (days)"