in diameter. For projectional reasons
this is considered the maximum limit in



size



'At the present time (June, 1926) three Zeiss Projec-
tion Planetariums are in operation hiesides the one in
Munich, viz., in Leipzig, in Barmen, and in Diisseldorf.
Others are being completed in Berlin, Hamburg, Frank-
fort, etc., and will be ready in the course of this year.
The Planetariuxn building in the Prinzessinen Park in
Jena has been finished since the writer's visit in 1925



Having read an enthusiastic descrip-
tion of the apparatus, and on account
of the confidence inspired by the fact
that it was made by the Carl Zeiss
Optical Works at Jena, I approached
this investigation with a tendency
toward a favorable consideration. De-
termining, however, to hold this inclina-
tion in check and to approach the
matter with an open mind, I made the
examination with care and thorough-
ness. As a result of this study I am
enthusiastically in favor of securing a
Zeiss Projection Planetarium for our
new astronomical hall. Judging from
the experience at Jena and at Munich,
I believe it will attract more people
to the Museum than anything we have
ever had here. When it becomes more
widely known, it is sure to come to
America. May the first one come to
the American Museum of Natural
History !



A Nature Trail in the Sky



By frank E. LUTZ

Curator, Department of Insect Life, Anioriean Museum



FOR more than thirty years I had
wanted to be able to recognize at
least a few constellations and to
call them by name. For more than
thirty years I had envied those who
could do it, but for some reason or
other — either laziness, or an inferiority
complex, or lack of proper inspiration,
but probably the first — I never really
learned any except the two northern
"dippers." Then, in March my small
boy asked me what a third dipper "up
there" was. The question challenged
my intelligence and was a call to do my
parental best. It does not take as
much work as I had thought; even I
have learned a few constellations;
and it is lots of fun.

"Nature Trail" has come to mean
to some of us a path in the woods or
fields with labels pointing out a few
of the interesting things along it, just
as a friend taldng a walk with us would
do. Let's make a "nature trail in the
sky." To fully enjoy this trail, lie
flat on your back on Mother Earth,
wrapping yourself in- blankets if neces-
sar3^ The effect is often magical, for
you seem to float across the sky from
one constellation to another.

Before starting on any trail we must
get our bearings, and knowing north is
very important. Fortunately this is
easy in the sky of the Northern Hemi-
sphere, where our present trail is
located. Polaris, the North Star, is
fairly close to the North Pole of the
heavens and will be as long as we live.
About 5000 years ago a star in the
Dragon's tail was the pole star and
12,000 years from now Vega in Lyra
will be the pole star. We shall point



out these stars shortly. The celestial
north pole moves in a circle that has its
center about half-way between Polaris
and Vega, one revolution taking about
26,000 years. For our present purpose,
however, we may consider that it is a
fixed point about a degree from Polaris
in the direction of Mizar, the second
star from the end of the handle in the
Big Dipper; and Polaris is the star at
the end of the handle of the Little
Dipper. The lip of the Big Dipper
points to Polaris.

Mention has just been made of a
"degree." Degrees are to the face of
the sky, as we see it, what feet or miles
are to earthly things, measures of dis-
tance. Stars millions of millions of
miles apart may seem to us to be very
close together and, if one star is nearly
back of another from the point at which
we stand, the two will to our unaided
eyes appear to be one star. From our
point of view, it looks as though we are
in the center of a huge, hollow glass
ball (the sky) that is revolving about
us and we can see about half of it at
any time. Of course, it is what we are
standing on that is revolving but that
does not alter appearances. The stars
seem to us to be on the shell of this
huge sphere.

Do not be discouraged by the follow-
ing geometry; we shall soon get to sky
measuring. There are 360 degrees in a
circle. Since we can at any time see
about half of any one of the great
circles in the sky, the length of a line
from some point on the horizon to the
horizon opposite the first point is 180
degrees. Clearly, then, if the apparent



412



NATURAL HISTORY



distance, the stars may be said to be 5
degrees from each other. But most of
us find trouble in estimating small
fractions of the distance from horizon
to horizon. Therefore, small measur-
ing rods here and there in the sky are
convenient. One such measure is the
depth of the bowl of the Big Dipper.
The two stars that mark the side
opposite the handle (the two stars that
point to Polaris, the North Star) are
about 5 degrees apart. The distance
from the tip of the handle of the Big
Dipper to the far edge of the bowl is
roughly 25 degrees.

Now, we are ready to take the trail.
First, we shall wander about in the
region of the Pole and later we shall go
to the Zodiac, the celestial menagerie
and the stamping-ground of the most
far-reaching fraud that ever dignified
itself by the name of a ''science,"
astrology. If you must believe in
something foolish, believe the stories
that I am going to tell you about the
Greek gods and goddesses, but do not
be so utterly foohsh as to tlink that
the positions taken by celestial bodies
in their set courses have any connec-
tion with the course of your body's
destiny, much less of your mind's.
The only explanation for the belief
in astrology by otherwise intelhgent
people of the present age is that
"Barnum was right."

It so happens that there are five or
six rather interesting constellations so
near the celestial north pole that people
throughout most of the northern half
of the world can see them at any hour
of a clear night in any season of the
year — they do not set below the hori-
zon. To learn these we do not need to
wait until certain hours of certain
nights, and, knowing them, will help
us to find the others. The accompany-
ing map (Map 1) shows approximately



the relative positions and distances
from each other of these stars. There
is no fixed up-and-down to this map
because, as our world turns, the map
must be turned to keep up with it.

Look at this map, paying special
attention to the two "dippers," includ-
ing Polaris, the North Star. More or
less ignore the other stars for the
present but turn the map around and
around, back and forth, until you can
pick out the two "dippers" wherever
they are. Then look up in the sky on a
clear night in a generally northern
direction and there you will see them.
That much I have known for thirty
years.

Our ancestors either had better
imaginations than we have or, being
interested in different things, their
imaginations took different turns. The
constellations that suggest dippers to us
suggested bears to them. Accordingly,
what we call the Big Dipper is a part
of what they called the Big Bear or, in
their language, Ursa Major. Our little
Dipper is their Little Bear or Ursa
Minor.

Furthermore, the ancient peoples
had stories to "explain" the constella-
tions that they recognized. Most of
these stories concerned their gods and
these gods had some very human traits.
Jupiter was king of the Greek gods and
Juno was his wife. There was a nj^mph
named Callisto, who interested Jupiter
so much that Juno became jealous.
Just what happened then is not any
clearer than many other family quarrels
are. The girl in the case, Callisto,
was changed into a bear and the bear
was put up in the sky where the stars
of Ursa Major, our Big Dipper, mark
its position. But, whether Jupiter did
it to avoid Juno's jealousy or whether
Juno did the changing in revenge and
then Jupiter did the rest, is not certain.



CEPHEUS



CASSIOPEIA\;f



"UHlcDippei^



AV^^o\^^



I Pol oris or North Star



«About3000 B.C. this was the North Star ^^^^LoZ: - - ^




,-'•0



V URSA MAJOR

\ or'Big Bear"



MAP 1



413



414



NATURAL HISTORY



Each of these Bears has an absurdly
long tail, the handles of the dippers,
and what we call the Big Dipper, for
example, is not all there is of Ursa
Major; other stars belonging to it are
shown in Map 1. The letters are the
Greek ones by which astronomers
designate the different stars of a con-
stellation. In Ursa Major o marks the
tip of the bear's nose. The only front
foot the beast has (possibly Juno saw
to the other one) is at l and k; one hind
foot is at X and n, the other being at
V and f .

When stars become very famous
they get names as well as letters. Map
1 gives, the names of three stars in our
Big Dipper. Of these, Mizar, the one
next to the end of the handle, is the
most important for us. What we call
Mizar is itself really a group of stars
but to some unaided eyes they look
like one; sharper eyes can see two, the
fainter of which is called Alcor; and
astronomical instruments show others.
At any rate, remember Mizar.

Incidentally, Polaris, the North
Star, is really a double star, having a
companion of ninth or tenth magni-
tude. The stars that appear brightest
to us are said to be of ''first magni-
tude." They are all named in the
accompanying maps and marked with
rayed dots. Most of the second magni-
tude stars are marked by dots with
circles around them and some are named
in these maps. A sixth magnitude star
is barely visible to us without a glass.

The Dragon (Draco) Ues with his tail
between the two ''Dippers" or Bears.
Opinion is not unanimous as to what
dragon this was in life. It may have
been the one that Cadmus killed,
and then, when he scattered its teeth
like seeds, an armed man sprang up
from each of them and gave him more
trouble. Or, it maj^ have been the one



that guarded the golden apples of
Hesperides and was kiUed by Hercules.
As we shall soon see, Hercules is now
not far away from it in the sky.

The tip of the Dragon's tail is
between Polaris and the bowl of the
Big Dipper, about eight degrees from
the Hp of the Dipper (remember that
this dipper is about five degrees deep).
Following the outline of the beast
toward its head we first go parallel to
the handle of the Big Dipper until,
when just between the bowl of the
Little Dipper and the crook in the
handle of the big one (the star Mizar)
we find the star a of the Dragon. It is
the one that was the pole star about
5000 years ago. In other words, the
earth is swinging about at such a rate
that the end of a straight line continu-
ing its axis until it meets what looks
to us to be the face of the sky has
moved from near this a star in the
Dragon to near the end of the handle of
the Little Dipper, our present pole star.
The course of the end of this fine (that
is, the path in the sky of a prolongation
of the earth's axis) is a circle. The cen-
ter of this circle is also the center of the
ecHptic, the apparent path of the moon
and the location of the Zodiac we are
going to see later. But now let us get
back to the Dragon or we may get lost.

We followed the outhne of the
Dragon from the tip of its tail near the
hp of the Big Dipper to a point be-
tween the handle of that dipper and
the bowl of the Little Dipper. Now,
stiU going toward the Dragon's head,
we curl around the bottom of the Little
Dipper's bowl, then double back so as
to make a rough S (turned right for
left), as is shown in Maps 1, 2, and 4.
The brightest star (7) of the four
which mark the Dragon's head may be
roughly located as foUows: Imagme a
fine drawn from Polaris to the end of



A NATURE TRAIL IN THE SKY



415



the Big Dipper's handle. This hnc
may be considered to be one side of a
nearly eqiial-sidod triangle of which
the other two sides meet at 7. So, 7
is about as far from either Polaris or
the end of the Big Dipper's handle as
they are from each other.

Cassiopeia is our next constellation.
Some see in it a sprawly W; others,
taking in one more star (k), have a
chair with an uncomfortable-looking
back (upside down in Map 1). How-
ever, Cassiopeia was a queen and she is
not sitting in that chair but the chair is
formed b}^ her bright spots. Her hus-
band, Cepheus, and her daughter,
Andromeda, are not far from her. We
shall meet them soon.

Well, Cassiopeia, the mother, is there
on the side of Polaris opposite the Big
Dipper and about as far from Polaris
as Polaris is from the Big Dipper.
Three of Cassiopeia's stars (a, /3, and 7)
are bright ones, being of second magni-
tude. Now meet her husband.

Cepheus, once King of the Ethio-
pians, is between his wife, Cassiopeia,
and the bend in the back of the Dragon.
That is rather nice of him and the best
that I have been able to learn about
him. After studying Map 1 you can
probably find hmi up there but, if you
need further help, note that five mod-
erately bright stars form a lop-sided
square with a triangle on it, the triangle
being on the pole-star side of the square.
The top of the triangle is nearly on a
line between Polaris and ^ of Cassio-
peia. The following is not usually
considered a part of this constellation,
but, 4 degrees from f, somewhat
toward a but outside of the square, is
one of the reddest stars that we can see
without a glass. Like most red stars,
it is a "variable," being brighter at
some times than at others.

There are other stars in this general



region of the north pole of the sky but
we must be going elsewhere, and now
we get into the trouble that the con-
stellations we are going to learn are
not always visible to us, owing to the
way our earth turns around and we
with it. First we shall take some con-
stellations of the summer skies at
fairl}^ reasonable hours of the evening.
Most of Cassiopeia and the bottom of
the square of Cepheus are in the Milky
Way and, for a while, we shall keep
either in the Milky Way or on the same
side of it as the stars we have been
looking at.

The Milky Way, or Galaxy, looks
very much like an irregular and in some
places a divided streak of hazy light
across the sky. It is a region where
there are millions of stars too faint or
too far away for our eyes to see them
clearly. One explanation is that the
universe is shaped like an enormously
large Ferris wheel. If such a wheel,
miles and miles across, were hung
full of lights and we were near its center
and looked along the axle of the wheel
we would see a large number of lights
(stars) but if we looked toward the rim
of such an immense wheel we would
see many more, most of them so far
away that they would be indistinct
(the Milky Way).

At any rate, in June the Milky Way
is along the eastern horizon at about 9
P.M. and nearly in mid-sky at about 1
A.M. (when the Big Dipper is west of the
North Star). In August at 9 p.m. it
is in about the same position as in June
at 1 A.M. At about midnight of about
April first or about 9 p.m. of the middle
of May, the Milky Way forms a border
along the northern horizon from East
to West; in other words, when the
Big Dipper is above the North Star.

Start at Cassiopeia, then go along
the Milky Way past her husband,



416



NATURAL HISTORY



Cepheus, and you will come to the
"Northern Cross," a part of Cygnus,
the Swan. ■ The head of the Cross
(Map 2, a) is toward Cassiopeia and
one arm of the Cross (5) points through
the head of the Dragon to the end of the
handle of the Big Dipper. Another
way of locating it is that the side of the
Big Dipper's bowl nearest the handle
points toward the foot of the Cross.
(Do not include here the very bright
star, Vega, that will be mentioned later
in connection with Lyra.) From a to |8
(the whole upright of the Cross) is
about the length of the Big Dipper.
Taking in the whole constellation, the
bill of the Swan is at ^ and its wings
stretch from k to n. It seems that
Cygnus was a friend of Phaeton, the
boy who went joy-riding with the
horses of the sun and got into fatal
trouble. Cygnus mourned so much
that Jupiter changed him to a swan.
They had a great way of changing
people into animals in those days, and
on almost any excuse.

Having seen the Northern Cross, we
shall now skip over two constellations
(coming back to them soon) in order to
see the Northern Crown (Map 2) . It is
a small (about the size of the bowl of
the Big Dipper) but a fairly complete
circle of stars that lies on the other side
of the Dragon from the North Star.
Imagine one line drawn from the bottom
of the bowl of the Big Dipper, through
the end of its handle, and then pro-
longed for about the total length of the
Big Dipper. It will end at about the
Northern Crown. If that is not enough,
imagine a second line drawn from the
end of the Little Dipper's handle (the
North Star) , through the bottom of its
bowl, through the back of the Dragon
and nearly as much farther. It will
end and meet the first line at the
Northern Crown. This crown was



given by Bacchus to his bride, Ariadne.
He probably put it in the sky for safe-
keeping.

In going from Cygnus to Corona (the
Crown) we skipped over Lyra and
Hercules. They have not been very
easy for me to make out since Lyra
seems to me rather indefinite and
Hercules rather sprawly.

As for Lyra, let us locate its brightest
star Vega and say that the rest of the
"Harp" is between it and the foot of
the Northern Cross. Vega is very
bright (first magnitude) and forms one
corner of a nearly equal-sided triangle
of which the North Star and the end
of the Big Dipper's handle are the
other corners. The side of the Big
Dipper's bowl that is nearest the handle
points fairly close to Vega, as I hinted
when trying to locate for you the foot
of the Northern Cross. The Harp is
supposed to be the one that Apollo
gave to Orpheus. Its music not only
charmed men and beasts but made even
trees and rocks get up and move
around. More than that, when the
wife of Orpheus died and went "where
Pluto held his sway," Orpheus fol-
lowed her and played so sweetly that
Pluto let her out. By the way, it is
said that Vega is 160 millions of
millions of miles from us but approach-
ing at the rate of 500 miles a minute.
It is at least 30 times as bright as our
sun and, as was said before, will be our
descendants' north star 12,000 years
from now.

I cannot help you much with
Hercules except to say that a part of
him is between Vega and the North-
ern Crown. Perhaps you will see four
stars there that mark the corners of a
rough square. The two that are farther
from the North Star than the other two
are his belt; the closer two are in his
legs, and his feet are near the Dragon




MAP 2



417




MAP 3



418



A NATURE TRAIL IN THE SKY



419



that he may have killed in addition to
doing man}'- other wonderful things.
Perhaps ]\Iaps 2 and 4 will help you to
get his various parts together.

Going on the other side of the
Northern Crown (Corona) from Her-
cules we find Bootes. Bootes is a
plowman and some have called the Big
Dipper his plow, but the constellation
looks more like a kite with a very
bright, first-magnitude star (Arcturus)
where the tail would be fastened and
with its head lying near and being
pointed at b}^ the handle of the Big
Dipper. (See Maps 2 and 3) . Arcturus
is said to be about 250 millions of
millions of miles away and approach-
ing us at the rate of 150 miles per
minute. It is about a milUon times as
large as our sun. We deal with large
numbers in the heavens. Another
name of this constellation is Areas. If
you look up the story of Areas, the son
of CaUisto, you will see why this con-
stellation is near the Great Bear — why,
that is, according to mythology.

Moving farther away from the North
Star, we come to a Snake (Serpens).
It has its head near the Crown (Corona)
and is being held by a man (Ophiuchus)
who is at the head of Hercules. The
combination is in honor of J]]sculapius,
the god of medicine (note the emblem
of the medical corps in our army) , but
we shall not stop to see the doctor and
there is a much better snake farther on.

Still going away from the North Star
in this same direction we come to the
Scorpion in the zodiac along the eclip-
tic; and the ecHptic is a ver}^ important
thing in matters of the sky. Let me
quote from Howe here so that if it is
wrong you can blame him.

''The zodiac, or zone of animals, is a
belt sixteen degrees wide, which ex-
tends around the sky like the stripe on
a croquet ball. From antiquity onward



much attention has been paid to the
constellations in it. Imagine that a
line from the center of the sun to the
earth's center is prolonged through the
earth and extended until it meets the
celestial sphere.

"While the earth travels round the
sun in its annual journey, the extremity
of this line traces a circle on the
celestial sphere. The name of the
circle is 'the ecliptic' To an eye situ-
ated at the sun's center the earth would
appear to travel around the ecHptic.
To an eye placed at the earth's center
the sun would similarly appear to
course along the echptic, taking a year
to make the complete circuit, passing
through the zodiacal constellations in
successsion. The ecliptic lies in the
middle of the zodiac, which extends
eight degrees each side of it. As we
watch the sun. moon, and planets, they
always appear to lie in the zodiac."

Since the ecHptic is a sort of a circle
and the zodiac is a circular zone, they
have neither beginning nor end and we
can break in at any point. But, since
it is not very comfortable to go star-
gazing just for the fun of it before
about the middle of May, we shall start
with that member of the zodiac that
sets in the West at about 9 p.m. then,
the Gemini or "Twins." However, I
suggest that you do not start on this
tour of the zodiac and the side trips
that will be taken in connection with it
until you have become well acquainted
with what has gone before, especiallj'-
with those stars shown in Map 1.
We are going to use the constellations
already mentioned as landmarks — or
"skymarks." When on a new trail,
one should be able to recognize such
things and, furthermore, if you learn
merely what has already been pointed
out you will know more about the sky
than most people do.



420



NATURAL HISTORY



The Twins, Castor and Pollux, may
be found as follows. Starting with
Mizar, the bright star that is next to
the end of the Big Dipper's handle,
follow a line from it diagonally across
the Big Dipper's bowl to the two stars
which lie in the front foot of the Bear
(see page 414); then extend this line abo at
25 degrees (about the total length of
the Big Dipper) farther. That will
bring you to the Twins. The rest of
the constellation is on beyond them
(between them and the Milky Way) and
may be recognized from Maps 3 and 5.

These boys were interesting brothers.
Pollux, represented by the brighter of
the two stars, one of first magnitude,
was immortal ; but Castor, represented
by a fainter star (really a double one)
near him and on the side toward Cassio-
peia, was mortal. Being mortal. Castor
died, and Pollux was so grieved that he
wanted to die too but, being immortal,
he could not do so without special per-
mission. Jupiter refused this permis-
sion but compromised by allowing
Castor to spend one day with Pollux
on Mt . 01 ympus , and Pollux to spend the
second with Castor in Hades, and so on.

The next constellation on the eclip-
tic, following the order in which they
arise in the East, is Cancer. This does
not mean that Cancer is always east of
Pollux as we see them in the sky — a
very confusing thing due, among other
things, to the fact that the ecliptic is
not parallel to the celestial equator. I
am far from understanding this fully,
but twirling the disc of the very useful
"Barritt-Serviss Star and Planet
Finder" has helped much.

Cancer in the sky is not a disease but
an animal, a crab. The stock explana-
tion of why this constellation was called
a crab does not appeal to me very much
and my own private explanation may
not be true, so I shall give neither.



although I may say that each is con-
nected with the habit crabs have of
going sideways. The particular crab
which this one is said to be is the one
that pinched Hercules when that famous
hero was fighting the nine-headed hydra.

None of the stars of Cancer is of
more than fourth magnitude. Five of
them (Maps 3 and 5) outline a Y and