**Study Guide for Test #1**

**Dr. J. R. Webb**

**Chapter
1 Our place in the Universe.**

** **

*Astronomy is an Observational
Science*- we cannot usually interact with our subjects.

The scientific method: 1. Observe some phenomena

2.Propose a hypothesis

3. Make a prediction based on the hypothesis

4. test the prediction

Some basic theories: Newtonian mechanics, Theory of Relativity, Quantum Theory

Theories are **ALWAYS**
subject to revision based on new data.

Basic math: Angular measure: 360 degrees (^{o})
in a circle

60 arc
minutes (‘) is a degree 60’=1^{o}

60 arc seconds (“) in a degree 60” = 1’

The Moon and Sun both subtend ~ 1/2^{o} (=30’) in the sky.

**Small angle
Formula**: Relates the apparent angular size to the physical size and the
distant of an object. If you know any
two, you can calculate the third.

D = Qd/206265

Where D is the physical size, Q is the angular size you measure, and d is the distance to the source. IF you measure d in meter, D will also be in meters. Q is always in arc seconds.

**1-6
****Powers of Ten Notation** **(Scientific Notation)**.* *

A method of writing and manipulating large and small numbers.

10^{0} = 1 10^{0}=1

10^{1} = 10 10^{-1}=1/10=0.1

10^{2}= 10x10=100 10^{-2}=1/(10x10)=1/100=0.01

10^{3}=10x10x10=1000 10^{-3}=1/(10x10x10)=1/1000=0.001

2,000,000 = 2 x 10^{6} 0.000002 = 2 x 10^{-6}

To multiply: multiply the leading numbers (numbers in front); add the exponents:

(2 x10^{12}) x (2 x 10^{6}) = (2x2) x 10^{12+6}
= 4 x 10^{18}

To divide: divide the leading numbers and subtract the exponents

(2 x 10^{12}) ** /** (2 x10

**Units:**

** **

Basic units: Distance – meters, inches, miles, etc

Time – seconds, minutes, days, years

Mass – Kg, grams

compound units: speed or velocity – km/sec, miles/hr

density – kg/meter^{3},
grams/cm^{3}

acceleration – m/sec^{2}

units peculiar to astronomy:

**Astronomical Unit** (AU) the average distance between the Earth
and the Sun, usually used in discussing distances within the Solar system.
1A.U. = 1.5x10

**Light Year **(1LY) the distance light
travels in one year in a vacuum. Used
for distance to stars and galaxies. 1Ly = 9.5x10

__ __

**Parsec **(pc)
the distance at which 1 AU subtends an angle of 1 arc second. Used for distances to stars and galaxies. 1
pc = 3.1 x 10

__ __

**Chapter 2**.__ __

__ __

* Constellations* – A collection of stars
that people see patterns in. Different cultures throughout history have seen
different patterns in the stars, so the International Astronomical Union
divided the sky up in to 88 “official” constellations to standardize them. Examples of constellations you might have
seen: Orion, Sagittarius, the big
Dipper.

* Celestial Sphere* –
An imaginary crystal sphere around the Earth onto which the stars are attached.

Celestial equator – The intersection of the plane of the earths equator and

the celestial equator.

Celestial Poles – The extension of the Earths rotational axis to the celestial

sphere.

* Ecliptic* – The
apparent path of the Sun along the celestial sphere or the plane of

the Earth’s orbit around the Sun.

* Seasons*- Changing
weather patterns caused by the tilt of the Earth’s rotational axis to its
orbital plane (the ecliptic).

Coordinate Systems-

Altitude-azimuth personal coordinate system important definitions-

**Altitude Astronomical Horizon**

**Azimuth
Zenith**

** **

Right Ascension – Declination coordinate system

Right ascension (like longitude except on celestial sphere)

Declination (like latitude)

Vernal equinox – starting point of right ascension and the point where the

ecliptic crosses the celestial equator going from south to

North.

Precession – The “*wobble*”
of the Earth’s rotational axis. **The
period is 26,000 years**! It is the ** direction**
the axis points,

** **

**Time. **Mean
Solar Day- exactly 24 hours by definition.

Apparent Solar Day- The time between two consecutive noon’s. Time

measured with respect to the Sun.

Sidereal
Day- Time measured *with respect to* (WRT) the “fixed” Stars.

23^{h} 56^{m}
long.

Sidereal Year. The time it takes the Earth to make a complete orbit around the

Sun. 365.2524 solar days long.

Tropical (seasonal) Year- The time it takes the Sun to come back to the vernal

equinox.

**Chapter
3.**

** **

** Phases of the Moon****.**

Lunar phases depend on the Earth-Moon-Sun position.

New
moon :moon is 0^{o}from
the Sun in the sky

1^{st}
Quarter :moon is 90^{o}
east of the Sun in the sky

full
Moon :moon is 180^{o}
from the Sun in the sky

3^{rd} quarter
:moon is 90^{o} west of the Sun in the sky

** additional
phases:** called waning gibbous, waxing gibbous, waning crescent and waxing
crescent.

**Moon’s orbit**:
Moons orbit is elliptical, and is at a 5^{o} angle with respect
to the cliptic plane. Moon orbits in an
eastward direction, and moves 13^{o} further east every day.

**Synchronous rotation**.- Moon’s rotational period is
equal to its orbital period so we only see one side of the Moon.

**Sidereal month** – one orbit of the Moon around the
Earth WRT the fixed stars.

**Synodic Month** – one orbit of the Moon WRT the Earth
Sun system (i.e. one complete set of phases)

**Eclipses**: __Solar
eclipse__- The Moon moves directly between the Earth and Sun.

1. phase must be New

2. line of nodes must point toward the Sun

__Lunar Eclipse__- The Moon moves through Earth’s shadow.

1. phase must be full

2. line of nodes must point toward the Sun

**Total eclipse**- observer is in the **Umbra**, or
darkest part of the shadow.

**Partial eclipse**- observer is in the **pneumbra**,
or lightest part of the shadow.

**Annular eclipse**- The angular diameter of the moon is
small (Moon is at **apogee**) and cannot completely cover sun in spite of precise
alignment.

Cosmology: The theory of the creation and evolution of the Universe.

Retrograde motion: The apparent westward motion of the planets among the stars.

**Geocentric cosmology – “Earth-centered” model – Ptolemy
(~100 AD) –** Had the Earth in the center, celestial sphere around the Earth,
and planets orbited the Earth.

**Heliocentric cosmology- “Sun-centered” model - Copernicus
(1543**) – The Sun was the center of the Universe. Copernicus determined: The order of the planets from the Sun, the
sidereal periods, and semi-major axes in AU.

**Tycho Brahe**-
(1547-1601) A great astronomer (not so great swordsman) who made
detailed (non-telescope) observations of the planets, the Sun, the moon and
meteors. Was the first to prove meteors
were actually no “Shooting stars” but space debris in our atmosphere and to
understand supernova are exploding stars.

**Johannes Kepler** (1571-1630) Used Tycho’s data to
deduce 3 laws of planetary motion.

1. The orbit of a planet around the Sun is an ellipse with the Sun at one focus.

2. The planets sweep out equal areas in equal times.

3.
**P ^{2 }= a^{3}** (sidereal period (yrs)
squared = the semimajor axis (in AU) cubed.

**Galileo Galilei** (1564-1642). First person to use a
telescope to observe astronomical things.

· Showed Venus orbited the Sun (had phases)

· Discovered 4 largest Moons of Jupiter

· Saw craters and mountains on the Moon

· Showed the sun had “Sunspots” and rotated.

· Started branch of Physics known as Mechanics (the study of motion).

Definitions: **Speed**,
**velocity**, **acceleration**, **momentum**

**Vector** quantities:
quantities that have both direction and magnitude “How much”

**Scaler **quantities:
quantities that have only magnitude “how much”.

**Isaac Newton** (1642-1727).