The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1899-09-20


fresult, they seem not to move at all
among themselves, and so we call them
fixed stars. Thew may, indeed, be in
motion, but their great distance pre-
vents our detecting it.
Now, stellar photographs are made in
much the same way as ordinary DOR
traits. Only, instead of using simple
camera, the astronomer exposes his
Photographic plate at he eye-end of a
telescope The sensitive surface of the
plate is substituted for the human eve.
We then find on the picture little dot
corresponding to every star WITHIN the
photogra pied region of the sky. But,
as every one knows, the turning of the
earth on its axis makes the whole heay-
ems, including sun, moon and stars,
rise and set every day. So the stars,
when we photograph them, are sure to
be either climbing up in the eastern sky
or else slowly creeping down in the
western. And that makes astronomical
photography very different from ordi-
nary portrait work. For the stars cor
respond to the sitter, but they don't
sit still. For this reason it is necessary
to connect the telescope with mechan-
ical contrivance which makes it turn
round like the hour hand of an ordinary
clock. The arrangement is so adjusted
that the telescope, once aimed at the
proper object in the sky, will move so
as to remain pointed exactly the same
during the whole time of the photo
graphic exposure. Thus, while the light
of any star is acting on the plate, such
action will be continuous at a single
point Consequently, the finished pic
ture VIII show the star as a little dot
If it were not for this arrangement the
star would trail out into a line instead.
of dot. Now, we have seen that the
planets are all slowly moving among
the fixed stars. So if we make star,
photograph in part of the sky where
planet happens to be, the planet will
make short line on the. plate. If the
planet remained quite unmoved rela-s
lively to the stars, it would give dot
like the star dots. The presence of =
line, therefore, at once indicates a
planet.
This method of nlanet-hunting has
proved most useful. More than 4e0
small planets similar to Piazzi's have
been found, though never another one
like Uranus and Neptune. But, as we
have said, these little planets lie be-
tween Mars and Jupiter. They evident
ly belong to a group or family, and
many astronomers have been led to be-
lieve that they are but fragments of a
former planet.
In August, 1898. however, one was
found by Witt of Berlin which will
probably occupy very prominent
place in the annals of astronomy. For
this planet goes we'll within the orbit
of Mars, and this will bring it at times
very close to the earth. In fact, when
the motions of the new planet and the
earth combine to bring them to their
positions of greatest proximity, the
new planet will approach us closer than
any other celestial body. except our
own moon. Witt named his new planet
Eros. The size of Eros is probably suf-
ficient to bring it within the possible
ties of naked-eye observation at the
time of closest approach to the earth.
The next favorable opportunity will
occur in November. 1900,. when the
planet will be observable easily from all
parts of the United States.
To astronomers the great Importance
of this new planet is due to the follow
ing circumstances: For certain reasons
we have not space to state in detail,
the distance from the earth to any.
planet can, be determined with degree
of precision which is greatest for plan-e
we shall learn the distance of Eros
more accurately than we know any
other celestial distance From this, by
a process of calculation, the solar dis
lance from the earth is determinahle.
But the distance earth-sun is the fun
damenta1 astronomical unit of measure.
Thus Wits new discovery, through
its effect on the unit of measure, may
be expected to influence every part of
the science of astronomy. Here once
more we have striking instance of the
reward sure to overtake the diligent
worker in science. A whole generation
of men will doubtless come and go be-
fore we shall have exhausted the scien-
tific advantages to be drawn from
Wits remarkable discovery of 1898.
HAROLD JAROBY.
Columbia University