iJ[MJ~

[f)[l£!\~~~c.\OOV~(W~@~

Program by: Kevin Bagley & David Kampschafer

Documentation by: Mary Lynne Sanford

All rights reserved Copyright (c) 1981 SYNERGISTIC SOFTWARE 5221 120th Ave. S.E. Bellevue, WA 98006 ( 206) 226-3216

Apple] [and Applesoft are trademarks of Apple Computer, Inc. (

TABLE OF CONTENTS LIST OF TABLES AND FIGURES

SECTION TITLE PAGE FIGURE TITLE PAGE List of Tables and Figures 3 1 Main Menu 6 I Introduction 5 2 Planet Symbols 7 II Getting Started 6 3 Phases of the Moon 11 Ill Using the Program 7 4 Mars Retrograde Motion ( 1973) 12 Menu Item 1: Planets and Related Data 7 Menu Item 2: Relative Sizes 8 TABLE TITLE PAGE Menu Item 3: Relative Orbits 8 1 Planet Orbital Data 9 Menu Item 4: Other Solar System Members 8 Menu Item 5: Planet Position 9 Menu Item 6: Terminate 10 IV Additional Solar System Information 10 The Ecliptic 10 Phases of the Moon 10 Retrograde Motion 11 Glossary of Astronomical Terms 13 Bibliography 16

2 3

4 4

clearly clearly

SECTION SECTION

ets ets

thing thing

of of gan gan

tional tional the the

fy fy

general general

tion tion

of of

Guide Guide

to to

tary tary mation mation

motion motion

respective respective

tem tem

planets, planets,

including including Menu. Menu.

on on

ner. ner.

illustrations illustrations

Uranus, Uranus,

Retrograde Retrograde

beyond beyond

The The

the the

The The

the the

After After

Another Another

For For

complex complex

around around

individual individual

moon. moon.

to to

Within Within

as as

positions positions

about about

you you

force force

originally originally

way way

(See (See

planets planets

your your

well well

condense condense

may may

labeled. labeled. Planetary Planetary

program program

appearance, appearance,

of of

are are

Neptune, Neptune,

using using

the the

I I

the the

orbits

will will

the the

the the

Illustrations Illustrations

them. them.

motion motion

Fig. Fig.

out out available. available.

the the

section section

as as

between between

be be

general general

which which

orbital orbital

planets planets

recent recent

in in

present present

sun sun

their their

in in

The The

found found

see see

planets planets

from from

program program

1.) 1.)

Alternative Alternative

. .

provides provides

came came

the the

the the

from from

Guide Guide

and and

Graphic Graphic

All All

will will

is is

From From

when when

Planetary Planetary

compare compare

complex complex

includes includes

tables tables

information, information,

relationships, relationships,

the the

Mariner, Mariner,

sky sky

night night

diagrammed diagrammed

the the

and and

in in

THE THE

the the

Pluto. Pluto.

time. time.

from from

aid aid

as as

a a

of of

presents presents

the the

sun sun

you you

this this may may

cloud cloud

hub hub

graphic graphic

you you

their their

information information

they they

you you

the the

illustrations illustrations

sky. sky.

of of

PLANETARY PLANETARY

viewing viewing

materials materials

astronomers, astronomers,

and and

interrelationships interrelationships

information information

Guide, Guide,

their their

you you

will will

Pioneer Pioneer

of of

phases phases

statistics statistics

be be

run run

in in

All All

moons, moons,

orbit orbit

of of

an an

our our

each each

displayed displayed

the the

our our

images images

starting starting

choose choose

find find

to to

matter matter

the the

planets planets

INTRODUCTION INTRODUCTION

orbits orbits

overview overview

choices, choices,

you you

galaxy, galaxy,

understanding understanding

of of

solar solar

listed listed

5 5

the the

lunar lunar

of of

and and

sets sets

of of

on on

program program

comets, comets,

the the

about about

the the

will will

of of

which which

the the

sun sun

observatories, observatories,

from from

on on

are are

about about

the the

are are

Voyager Voyager

system system

for for

of of

in in

moon moon

each each

and and

the the

planets planets

of of

find find

GUIDE GUIDE

e.g. e.g.

relative relative

comets, comets,

also also

is is

the the

visible visible

data data

each, each,

in in

any any

solar solar

a a

the the

set set

and and

Milky Milky

illustrated illustrated

solar solar

is is

5 5

date date

a a

of of

one one

it it

bibliography. bibliography.

and and

is is

the the

clear clear

presented presented

billion billion

date date

of of

ranging ranging

members members

of of

probes. probes.

easy easy

the the

holds holds

system system

asteroids, asteroids,

and and

located located

to to

sizes sizes

data data

you you

asteroids, asteroids,

the the

information. information.

Way, Way,

these these

planet planet

Planetary Planetary

the the

planets planets

from from

and and

and and

descriptive descriptive

to to

years years

movement movement the the

of of

will will

to to

in in

from from

locate locate

naked naked

Additional Additional

in in

and and

phenomena. phenomena.

about about

convenient convenient

NASA NASA

of of

the the

within within

the the

at at

view. view.

a a

planets planets

to to

choose; choose;

The The

showing showing

our our

later later

ago. ago.

the the

a a

probably probably

planets, planets,

information information

Guide Guide

illustrations illustrations

year year

eye eye

time time

and and

two-thirds two-thirds

Planetary Planetary

The The

solar solar

missions, missions,

sun, sun,

informa­

sections sections

Gravita­

section. section.

of of

in in

except except

1 1

identi­

plane­

infor­

or or

com­

Main Main

man­

their their

their their

A.D. A.D.

first first

The The

sys­

and and

and and

be­ all all SECTION

gin

the

in

tion

cases.) tion. to

remain

procedure

have

one

RAM,

If

this

some

The

The

press

directions

using

character.

from

chosen.

From

does

and

Planetary

in

Planetary

sections

RETURN

The

the

II

the

is

one

3)

6) 4)

5)

2)

1)

not

any

to

...

......

... After

...

in

drive

Main

Planetary

Direction

disk

work,

re-run

of

.

the

when

Guide

PLANETS OTHER

TERMINATE

PLANET

RELATIVE RELATIVE

Guide

the

after

drive.

while

that,

Menu

DOS

re-boot

the

entering

section

Main

an

requires

to

Guide,

(Disk

using

you

The

SOLAR

section

by

POSITIONS

entry

press

AND

Menu

the

pressing

SIZES

ORBITS

programs

will

options

PLANETARY

an

the

Operating

Main

insert

.

disk.

GETTING

an

RETURN

by

Figure

item

RELATED

(Pressing

SYSTEM

see

MAIN

program. will

Apple

typing OF

6

Menu

the

the

OF

and that

on

appear

are

PLANETS

1

System)

MENU

number

the

option

PLANETS

boot

on

could RETURN

II

will

"RUN",

STARTED

MEMBERS

For

GUIDE

DATA

with

Main

on

a

appear

DOS

the

accidental

the

possibly

list

3.3

in

Applesoft

Menu,

then

disk.

front

screen.

3.3

may

for

manual.

on

format

that

pressing

contain

the Boot

of

be

it

RESETS

Enter

is

the

necessary

firmware,

screen

The

particular

not

according

disk.

section

RETURN.

more

disk

your

necessary

the

in

To

these

with­

must

48K than

sele­

best

you

sec­

be·

to

SECTION

tain

sired.

prog

Menu

for t

the

and

planet

tween planet, the

he

Following

After

PLANET

Mercury

Venus

Earth

Mars a n

list

great

r

continuity

its

am

u

listing

At

Item

mber

tiny

appea

of

such

table

will

every

entering

disparity

Ill

planets,

1

Mercury

of

of

:

list

as r

The

s

Planets

of

t

point symbols.)

he

on size

of

available

statistics.

Planetary

this

press

planet

information,

the

,

among

(4878

orb

where

and

option

screen

i

RETURN.

tal

SYMBOL

about

choices

Press

Related

the

km)

(f)

~

Cl cf

period, you

Guide

This

you

along

planets,

Planet

the

and

which

USING

but

make

clearly-you

table

Data

will

Figu

space

sections

mighty

etc.

sections

with

Symbols

you

7

a

see

r

such

gives

e 2 e

THE

Studying

choice

bar

PLANET

Jupiter

Saturn

Pluto

Uranus

Neptune

its

wish

a

Jupiter

in

as

for

listing

un can

physical

PROGRAM

press

the

the

to

i

of

information

versal

be

this

order

learn,

section

(14,300 difference

the

of

viewed

characteristics

data

the

symbol.

desired

listed

and

or

nine

gives

km).

in

about

an

sub-section,

in

provides

SYMBOL

key.

any

(See

planets.

image

some

diameter

To

\V

4-

the

R

0

order

return

B

Figure

of

of

idea

planet

a

Press

each

tha

cer­

the

de­

be­

of

to

2

t Menu Item 2: Relative Sizes TABLE 1 PLANET ORBITAL DATA This option will assist you in visualizing planetary size. Here, the program asks if you wish to view one planet, two for comparison, or all. The indica­ ted planet(s) will then be drawn on the screen, again with their universal DISTANCE FROM SUN SIDEREAL PERIOD symbols (see Figure 2). PLANET AU 106 KM YEARS DAYS Menu Item 3: Relative Orbits '1) Mercury 0.3871 57.9 0.24085 87.97 The information in this section illustrates the position of the planets in re­ 0.7233 108.1 0.61521 224.70 ~ Venus lation to each other. Here, there is a choice of viewing all nine planets, the Earth 1.0000 149.5 1.000039 365.26 inner four, or outer five. Viewing the planetary orbits by inner four or oute r Mars 1.5237 227.8 1.88089 686.98 five at a time gives an improved scale while viewing all nine at once gives some Jupiter 5.2028 778 11.86223 indication of the tremendous distances involved. After requesting one of Saturn 9.5388 1426 29.4577 these options, the program will draw the orbits of the planets as seen from an Uranus 19.182 2868 84.013 oblique angle. This angle is necessary to give maximum view since the planets' Neptune 30.058 4494 164.793 orbital sizes vary so greatly. Also, the great eccentricity of Pluto's orbit actu­ Pluto 39.439 5896 247.686 ally causes it to cross that of Neptune. Sub-section #4 of Relative Orbits is provided to give an understanding of For the mean equator and equinox of 1960. Source: Supplement to the various orbital speeds of the planets. After selecting this option, you wil l The American Ephemeris and Nautical Almanac. key in a time increment (the amount of time between each positioning of the planets). The screen will then show the sun and the planets below it in order of closeness to the sun. The scale is not true, but spaced so that you can more easily place each planet. The planets will begin to move and, with each move­ Menu Item 5: Planet Position ment, the number of elapsed increments (week-month-year-decade) wil l be displayed. For true planet postions, see option #5 on the Main Menu or refer This section offers several ways of viewing the planets in relation to each to Table 1 which lists both distance from the sun and orbital period of each other. Choosing the inner fou r, outer five, or al l planets, the program can planet. draw either a representation of the planets as they orbit the sun, or the plan­ ets as they are seen in the night sky within the constellations of the ecliptic Menu Item 4: Other Solar System Members (see section IV). The orbit opt ion shows relative orbit position at a specified date to aid in spatial orientation of planetary position for that date. (You also This section offers information on the sun and the moon, satellites of the key in a time increment and a choice between a stationary or dynamic view.) planets, asteroids and interplanetary dust, and comets. The options are avail­ The constellation option allows you to display the night sky with planets able by indicated number; further directions are given on the program as you shown in their correct position for the specified date. Press the space bar to proceed. see a table of right ascension and declination for the indicated planets. These The sun-moon section provides text on both of these bodies, also a graphic values will help you locate the planets in the sky using a telescope. demonstration of the phases of the moon. Under the constellation option, the selection of t/1, Information, will pro­ The satellites sub-section lists the planets; you press the number of the vide a list of all the planets' locations within constellations as of your speci­ planet to see information about its satellites or moons. Statistical material fied date. If you select a constellation number, you will see a graphical rep­ about them will appear on the screen, one satellite at a t ime, beginning with resentation of the constellation and the planets within it. Note that only the the one nearest the planet. As directed by the program, press any key to go_ 1 constellations of the zodiac are listed because the planets only appear within from one satellite to the next. This material will help you appreciate how j the belt of the zodiac (the ecliptic). The planets maintain their positions in much the satellites vary. For instance, Saturn and Jupiter both have moons the constellation as it appears to move across the sky during the night. that are larger than the planet Mercury, yet some moons are smaller than A demonstration of retrograde motion is included in section 5. Retro­ many asteroids. When the list is complete, pressing any key returns you to grade motion is an apparent phenomenon occuring when the Earth, which is the Other Solar System Members Menu . moving faster around the sun than the outer planets appears to stop its reg­ Descriptive information about asteroids and interplanetary dust is avail­ ular eastward motion through the sky and go backward for a time. (For a able in that sub-section. more detailed explanation, see section IV, 3.) The comet sub-section offers graphic displays of a comet itself and the The program presents a model of retrograde motion by placing the sun in path a comet takes when entering the solar system, as well as textual informa­ the Earth's orbit. As you view the planets in motion, then, it is as though tion. The program indicates which keys to press for each option. they are orbiting the Earth. You observe all of the outer planets' retrograde

8 9 \

motion tion

Menu tion

ever, planet

terminated

an operating

be

it

The

the stellation

constellations

the

called

solar Phases plane

ecliptic.

We

moon, takes of tioned the of Looking tions planets

constellations

the

by

To

asked

The arbitrary

the The

As

its

celestial

moon.

same

refer

sun, Ecliptic is

changes

corresponds

the

eclipses

Item

it

of also.

terminate

the

the

occurring.

to

Of

zodiac sunlit

in

Earth

and

twelve

as

out

of

Of program.

ADDITIONAL

at

to

the

we

to

system

a

plane;

The in

move

moon

zone , it

6:

this

As

our

straight the

sun,

of verify

the

point

sphere

this

turn

would

see by

occur

and

ecliptic,

Terminate

hemisphere

were define

Moon

this the

constellations

are

sun

solar

way,

twelve,

"zodiakos

in

the the

as

view the

revolves

all more

The

back

the

during

in

your

Earth

zone

used

from

when

given is

a

illustrated line

appear

of

program,

instead

time

system

the

moon this

other

called

curly-cue

ture

except

of

to

closely

the

.

with

seven

choice

only

Earth,

rotates

program.

mystical the

the

around

normal, plane

the

depending

increment

SOLAR

appearance

kyklos"

planets

sunlit

from the

revolves

of

can

the

of moon

moon,

year.

Pluto

were

to

enter in

SECTION

as

with

by

ecliptic,

it

during

and

the

moon

around

always

the

Figure

the

convenient hemisphere appears

this

removing

significance,

simply

Proper

revolve

said

is

(circle

The

zodiac

are

whose

#6

a

and SYS

diagram around

10

you

on

on Earth,

central

Y

of

on

the

collectively

and

from

to

3.

be

the

or projection

or

the

the

T

removing

to

retrograde

termination

the

specify,

of around

are

IV

For

represent

found

time

extreme

EM

the

near

N.

we

is

sun,

be

other

Earth

presented

relative

animals).

-

the

areas

opposite

position.

so

The

arranged

but

special

example,

in

see

INFORMATION

what

it.

period

the

named

Main

a

the

in

for

the

program

partial

in

the

given

of

larger

of

referred

eccentricity

motion

one sun

animals,

positions

sun

we this

returns

astronomical

conditions

the

side

disk

model

In

reference.

in

successively

Menu.

As

that

because

appears

when

constellation

of

call

within

Section

or views,

astrology,

plane

orbital

the

of

should from

the

in

to

smaller

retrograde

the

the

and

the

will

You

the

planet's

they

of

as

12

also.

all

8

as

occasionally

in

the

computer's

placed

Full

the

plane

Earth

IV,

the

All

the

degrees

sky,

cause always

each con­ each

will

lunar

study

constella­

phases

along

the

are

portions

drive

3.

Twelve

zodiac.

Greeks

of

Moon.

in

Earth,

how

posi­

then

from

onto

signs

posi­

mo­

into

the

this and

the

the

the

be

at of

of

­

sun, tire Quarter around Gibbous days entire achieved

or at sunlit we

again through ing the New

Moon round than tion. or tion

tion across

Retrograde

0

Almost

twenty-two

The

As Beginning

As weeks,

total

see

the

sun

darkened

.

of

since

we

Earth)

Moon

MOON~

a

Later

But

C

the hemisphere.

we

lighted is

U

the

the

L

almost

New

Full

moon

Mars ()

the

L

phase,

and

solar see

visible

the

phase

one

/

view

moon

they

at

Earth

the

/ .

sky. halfway

Motion

they

sun,

Moon.

appear

~

Moon

the

the

against

Most

Waning

certain

at

quarter

hemisphere

side

then

eclipse.

a

and

0

plane

the

days

-we

travel

-

the

full

Figure 0

but -until

moon,

Full

moves

resume

.

this

of

is

A

from

planets

to

proceeds !2---()--w~

G>BOOUS

u

time

the

circle in

G

WAX

occasionally

during

visible. see

I

intervals

Crescent

of

BBOUS few

Moon

eastward

of

the

stop

is

I Eclipses

NG

--·-

its

4

on

we

stars

it

a

its the its

Earth

their

the

days is

illustrates

time

circle

as

is

and

from

around revolution

see

revolution

orbit turned

-

which

Waxing

again

Phases

At

through

in

in

moon

direct

the

the

EARTH

we

phase

relative

move

of

after

a

the

the

1973.

this

slightly

Earth,

lunar

it

is

see

the

Figure directly LASU""

Moon ()

outer

f1RST

the

to

Waxing

we

of

moon

goes ()

is

this ~ u

Crescent.

at

time,

the

motion,

backward

-

11

its

it

us,

QUART

sun

the

between

the

around

to

eclipse.

Earth

again

a

<

we as

flattened

the -

Waning

phenomenon

New

3 is

E

planets

in

slightly making

the

R

Moon

if

a only

passes between

moon

opposite

Gibbous,

observe

T

front

semi-circle.

:

last

the

see

creating

stars we

:

After

Moon,

R

the

O

for

the · Lunar

occur

earth

-

few

Gibbous

can

it

a

(those

slightly

higher

on

of

passes

in Earth.

CRES

CRESCENT

WAXING

a

invisible.

the sun semi-circle.

u.

that

seven

the

the

time

to

one

days

what

C

a begin

eclipses

EH

an

passes

during

with

•

sun narrow

/MOON

its

and

~

sun

I)

sun

farther angle

over

apparent

side.

through

above It

-

days,

phase

of

is

Last

to

and

is

the

in the

in

creating

directly

This

called

its

the

a

then

occur

see

Then

than

the

retrograde

section

period

Quarter

It

the

the

apparent

or from

during

Earth,

revolution

()

New

phase

parts

then

zigzag

sky

its

in

direct

below

Earth

Moon -

is

NEW

at

only

between

a

TOWARO

T:w

its

Waxing

•

the

of SUN

Earth's

fifteen and

-

u:•

partial

Moon.

of

its

of which

passes

phase

is

-

First o

days

path

dur­

mo­

mo­

mo­

and

the the

the sun the ~

has

en­

its

a­ GLOSSARY OF ASTRONOMICAL TERMS

ALBEDO: The fraction of light which a body reflects of that which falls on it. The higher a body's albedo, the brighter it appears in the sky compared to other bodies of the same distance from the sun. ALTITUDE: Angular distance above or below the horizon, measured along Figure 4 a vertical circle, to a celestial object. Mars Retrograde Motion (1973) ASTEROID: Synonym for minor planet. ASTRONOMICAL UNIT (AU): The approximate distance from the sun to the Earth. CELESTIAL EQUATOR: The projection of the Earth's Equator onto the celestial sphere. CELESTIAL SPHERE: The apparent sphere of sky and stars that surrounds 'f ', • ·· ------· Earth. I I I COMET: A small body of ice and dust revolving around the sun, sometimes -:. I • developing a 'tail' pointing away from the sun when near perihelion •'... I ' (closest approach to the sun) . I , PEGASUS : I I CONSTELLATION: A configuration of stars in a certain limited region of the • I I I I sky, regardless of their distance from Earth. JANl I 0 I ~------· CRATER: A more or less circular depression on the moon or other solar sys­ tem member caused by volcanic activity or meteor impact. PISCES • DECLINATION: One of a system of coordinates, along with right ascension, SEPT 1 -...... _ ,• that is measured on the celestial sphere instead of on Earth, as latitude and ---·-~------...--...,...-•, / - longitude. The position of a star or other point is measured on an hour I - .....~ I ' I< circle north or south of the celestial equator . .__--.-'I / ECCENTRICITY: The degree to which the orbit of a revolving body is oval, ', JU LY 1 or elliptical, instead of round. •. ~ , ECLIPTIC: The area in the sky where constellations of the zodiac, planets, ', ~"' ' the sun and moon are observed, since the orbital planes of the moon around the Earth, and other planets around the sun, etc. roughly corre­ '' '~----.---.''------.. -~ spond. (See explanation in Section IV, Other Solar System Information.) ' \ CETUS EQUATIONAL INCLINATION: The tilt of a rotating body's equator as com­ • • pared to its orbital plane . • EQUINOX: One of the intersections of the ecliptic and celestial equator. The two equinoxes are the vernal equinox (the advent of spring) and the autumnal equinox (the beginning of fall). ESCAPE VELOCITY: The velocity needed to escape the gravitational pull of Retrograde motion occurs when the Earth, which is moving faster around a body. the sun than the outer planets, overtakes and passes one of them. As the ESTRASOLAR: Outside of the sun. Earth passes, the outer planet is in opposition, that is, it is in a straight line HORIZON: An extension onto the celestial sphere of the Earth's horizon. with the Earth and Sun, with the outer planet and sun on opposite sides of INCLINATION OF ORBIT: The difference in angle of orbits between are- the Earth. Against the backdrop of distant stars, the outer planet appears to volving planet or body and the ecliptic. stop and move westward, or backward, during this period of opposition. As INTERPLANETARY MEDIUM: The sparse distribution of gas and solid par­ the Earth moves on around the sun and out of opposition with the outer ticles in the interplanetary space. planet, the outer planet appears to resume its eastward motion across the sky. KELVIN: The temperature scale most often used in astronomy . It measures The same apparent phenomenon occurs as you overtake another car travel­ temp erature from absolute zero (-273 degrees C.=O degrees K.), the point ing in the same direction on the highway. As you approach it, the other car at which all molecular activity stops. moves in the same direction as your car against the landscape. As you pass it, LIGHT YEAR: The distance light travels in one year or roughly 5.88*10e12 it appears to be moving backwards in relation to the more distant landscape. miles or 5,880,000,000,000 miles. If you look back after you have passed, the other car again appears to move forward. ,

12 13 MAGNITUDE: A measure of the amount of light received from a star or VELOCITY OF ESCAPE: The speed with which an object must move in other luminous object- its relative brightness. order to enter a parabolic orbit about another body, and hence move per­ MASS: A measure of the total amount of material in a body; defined either manently away from the vicinity of that body. by the inertial properties of the body or by its gravitational influence on VISUAL MAGNITUDE: A measure of the amount of visible light received other bodies. from a star or other luminous or reflecting body. MEAN DENSITY: The ratio of an object's mass to its volume. A density less ZENITH: The point exactly overhead in a line extended upward from Earth than one will float in water while greater than one will sink. to the celestial sphere. At the Earth's North Pole, an observer would see METEOR: The luminous phenomenon observed when a meteroid enters the the north celestial pole directly overhead (at zenith). Earth's atmosphere and burns up. ZODIAC: A belt around the sky centered on the ecliptic within which the 12 METEORITE: A portion of a meteoroid that survives passage through the constellations are found. The sun and the planets, with the exception of atmosphere and strikes the ground. Pluto, are always seen within it. METEOROID: A stony or metallic particle in space before any encounter with the Earth. MINOR PLANET: Synonym for asteroid. One of several tens of thousands of small planets, ranging in size from a few hundred kilometers to less than one kilometer in diameter. Most minor planets in our solar system orbit between Mars and Jupiter. OBLATENESS: The amount of flattening that occurs at the poles of a rotat­ ing body. PERIOD OF ROTATION: The time required for one complete rotation. On earth, this is one day. PLANET: Any of the nine largest solid bodies revolving about the sun. RETROGRADE MOTION: An apparent westward motion of a planet on the celestial sphere or with respect to the stars. (See Section IV, Other Solar System Information.) RIGHT ASCENSION: One of a system of coordinates, along with declina­ tion, that is measured on the celestial sphere instead of on the Earth, as latitude and longitude. Right ascension is the position of a star or other point measured eastward to the hour circle of the star from a reference point (the vernal equinox) on the celestial equator . SATELLITE: A body that revolves about a larger one; for example, a moon of a planet. SEMI MAJOR AXIS: In an elliptical orbit, the distance from the center of the ellipse out to one end of the orbit. SIDEREAL PERIOD: The period of revolution of one body about another; in our solar system, the time required for a planet to make one revolution of the sun. SOLAR SYSTEM: The system of the sun and the planets, their satellites, the minor planets, comets,meteoroids, and other objects revolving around the sun. SOLAR WIND: Charged particles ejected from the sun and flowing outward in gusts throughout the entire solar system, traveling at speeds between 200 and 400 miles per second. SPECIFIC GRAVITY: The ratio of the density of a body or substance to that of water. SYNODIC PERIOD: For planets, this is the interval in which the Earth gains a lap on one of the outer planets; or in which Mercury or Venus gains a lap on Earth. TROPICAL YEAR: Period of revolution of a body about the sun with re­ spect to a fixed location in space (vernal equinox).

14 15 j? !t l

Bl BLIOG RAPHY

Abell, George 0., Realm of the Universe, New York: Holt, Rinehart and Winston, Inc., 1976.

Alter, Dinsmore, et. al., Pictorial Astronomy, New York: Lippincott and Crowell, 1974.

Beatty, J. Kelly, et. al., The New Solar System, Cambridge, Mass, Sky Publishing Corp., 1981

Huxley, Julian, Space, London: Aldus Book Ltd., 1968.

Menzel, Donald H., A Field Guide to the Stars and Planets, Boston: Houghton Mifflin Company, 1964.

Moore, Patrick, The Atlas of the Universe, Rand McNally, 1970.

Moore, Patrick, The Observer's Book of Astronomy, New York, Frederick Warne 6 Company Ltd., 1971.

Nicholson, ian, Exploring the Planets (Life Science Library), New York: Time Incorporated, 1966.

Ridpath, I an, Ed., The Illustrated Encyclopedia of Astronomy and Space, New York: Thomas E. Crowell Co., 1976.

Sagan, Carl & Leonard, Johnathan N., Planets (Life Science Library), New York: Time Incorporated, 1966.

16