Herald and news. [volume] (West Randolph, Vt.) 1878-1943, 1894-05-31
A LEssoN IN AsTRoNoMY.



WAYS Convex.
I was talking one evening with
bright. intelligent boy Of fifteen. about
some of the more familiar astronom-
zeal subjects, when he surprised me
greatly by question that he asked.
Nv surprise arose from the fact that !
knew the boy to be a good student,
who stood well in his classes and that
he should he ignorant Of SO simple a
thing as that aboi 3 which he asked the
question seemed aSlost incredible.
Since then, however ] have found
that there IS a general misrepresentation
Of the subject, not only among boys
and girls but among grown people
and tits the purpose of this short ar
ticle to give simple explanation OF j,
Here IS the question asked i;y my
Young friend. I'VE are told that one
proof Of the earth's spherical form IS
the round shadow that it throws upon
the moon. but when the moon Is half
.fnlr the edge of the shadows IS
straight. and when II is three'quarters
fulr the edge Of the shadow IS con-
cave. Now, why is the shadow not al
ways convex, as ~ u Wieh INC i'''-
| Is seen as crescent
The boy thought, as You see, that
| the moons phases are caused by the
interposition Of the earth's shadow. a
little reflection will show you that this
is simply impossible. Let me see II !
can not describe the phenomenon SO
that you may draw mental picture
Of II.
You are standing, we viii say on
big ball out in space. Away of yonder
is another big ball. glowing with light
Between you and the glowing ball IS a
smaller. but non-luminous one. As the
la tter emits no light of its own, the side
that is toward you is dark and Of course
YOU can not see It.
This is the phase called the new
moon" The bali on which you stand IS
the earth. the glowing ball is the sun,
and the dark ball between you and the
sun IS the moon. The other side OF the
moon. the side toward the sun, il bright,
for the sun is shining on it At this
time the three balls are almost in a
straight line with each other, rs
In a few days the moon, which Is
perpetuallv revolving around the earth
from west to east, moves above the
straight line enough for you 70 catch
the first glimpse of its illuminated
side. and YOU see il as a thin crescent
Every dav il moves higher and you see
more and more of its bright side.
when i, reaches point directly over
! bead Won see one-half of that side
which is one.fourth of the sphere, anC
: when 1t begins to 90 down on the othe
side of the earth from the sun, tn
bright part becomes convex and tn
dark part concave. of course. When
[ gets down far enough on the side OF tn
earth away from the sun TO be in a lin
| with those two bodies, you see all it
illuminated side, and then it is full
moon.
As IL continues in its course aroun
the earth. the same phases are passe
? through. but in reverse order.
1t is very plain, then, that the shac
- ow of the earth does not cause tn
moons phases. Sometimes, however
the moon. in its monthly revolution
moves in the same plane as the earth
orbit. and gets into its shadow The
we have lunar eclipse. At no otht
time does the earth's shadow touch II
moon.
To make this still palmer. let me r
) mind You that when the sun is in IL
west. the earth's shadow must nece
i, sarilv be thrown out into space towai
- the east. But the crescent moon
seen in the west. you know-how, the
)r could it be caused by shadow that
away off in the east, on the other si'
of the ?-Worthington's Mag
4. zine.