The Washington times., 1922-09-20
Power of Telescope
AND WHAT THEY ARE ABLE TO REVEAL,
A Reader of Prof. Seryiss' Column
Wants to Know Strength of the
Big Lens at Lick Observatory.

round hole in the iris called
the pupil, which, on the aver
age. is from, a fifth to q quar-
ter of an inch IN diameter. Since
the light VARIES with the'square OF
the diameter II we have a tele-
scope one inch in, aperture, and
the pupil of the eye is one-fourth
Of an inch, the light-gathering
power Of the telescope. win be to
that Of the naked eye as sixteen 10
one. For terrestrial seeing, by
daylight, II is probably twenty
five to one. for in a bright light the
pupil contracts to a fifth OF an
inch, or less. .r 49,.
Now, the object-gla OF the
Lick telescope being thirty-six
inches in aperture. which Is. at
least 144 times the aperture OF the
pupil, its light-gathering power
must be the square of 144. or 20,73b
times that of the naked eye. II no
light were lost in transmission
through the glass, the telescope
should, therefore, show stars
10000 times fainter than the faint
est that the unaided eye can see.
This brings into view millions
of stars where the eye sees only
a few thousand. It also enables
the telescope TO penetrate" INFO
enormous depths of space that
may appear black and starless to
the eye alone. Thus a star that
lies lust at the limit OF visibility
to the naked. eye would, II re-
moved to n distance about 140
times greater, stiIl be within the
range of the Lick telescope.
In viewing the sum-. the moon
and the planets. all of which. ex.
hibit more or less extended disks,
the light gathering power Of the
telescope enables the astronomer
TO magnify the image many fold
without rendering il too faint to
be clearly seen. Experience has
shown that the -1nagnifying power
that can be effectively used with
. any telescope bears a. pretty reg
uiaf ratio TO the aperture, snarnely
about fifty or sixty diameters to
the inch. Under very exceptional
circumstapces. and only for par
ticular objects, a power as high
as 100 diameters to the inch Of
aperture may occasionally be en-
DiOltu. vi PoA pOSce
the astronomer does not often 60
beyond 900 or 1900 diameters
with even the largest telescopes.
II we take sixty as the average
maximum magnification. then the
bower Of the Lick telescope may
be put at about 2.100 diameters.
II II were practicable to press the
magnifying to the theoretical
limit. the power would be $500
diameters.
People often ask: How close
does such or such a telescope
bring the moon, or a given planet?
The answer is easy, depending
simply on the magnificatioh
used. The rule is to divide the
known distance of the moon, or
the planet. in miles by the num-
Der of diameters its image Is
magnified, and the quotient will
be the apparent distance in miles
as seen through the telescope.
But because of loss Of light, dis
tortion of image. etc, the dis
tinctness of the object in the
telescope is never as great as IL
would be in a. naked-eye view
taken at that same distance.
To ILLUSTRATE the rule. IL the
magnificati9H ~ 240 diameters
the moon will be seen as IL only
1000 miles away, instead of 24o,-
600, its real distance. A power Of
$50 diameters brings the planet
Mars, now about 50,0O0,00 miles
away, up to a distance Of about
| 200 900 miles.
You ask about the usefulness
Cor astronomical observations Of
telescope OF ''3s-power" by
which assume that pon mean
magnifying, power. A well-ma ade
object glass Of one inch aperture
would easily bear such a power
as that. II is about the power
of the best telescope that Cali
leo Succeeded in making, and bis
success In celestial discovery is
a warrant that you could not fail
TO see something very interest.
ing with the little glass in ques.
ton.