The Washington times. [volume] (Washington [D.C.]) 1902-1939, 1902-12-03
BEAUTIES OF DECEMBER SKIES

star close to II. The measure showed
that the faint star, far from being behind
the other. was actually the nearer Of the
two. But by choosing several small stars
and measuring from them all. this source
OF error can be pretty well done away
with.
The Whole observed change Of bearing
Of the star IS evidently equal TO the
angular diameter OF the earth's orbit
as seen from the star. Half OF this or
the radius Of the earth's orbit. as seen
from the star. is called its paranax.
The nearer a star Is the greater its
Darallax VIII be.
The Nearest Star.
By the methods outlined above. the
distances Of a considerable number OF.
stars have been measured. The nearest
one is Alpha Centauri invisible in our
latitude whose parallax is three-quar-
tiers Of a second Of arc. corresponding
to a distance Of 275, 900 times as great
as the suns.
The most convenient unit for meas
uring these great distances is the light
year-the distance light travels IN a
year. This is about $1,000 times the
suns distance. so that II We made a
map on such a scale that the earth was
one inch from the sun. a Iight-year
would be represented on the map by
one mile.
Alpha Centauri IS a little over four
light-years distant. Sirius. whose par
allax is half as great OBJ seq is twice
as far away
If star is over 100 ight-years dis
tant, its parallax is too small to be
measured, and we must remain ignorant
OF its true distance. This is the case
for some Of the very brightest stars,
and for the vast majority OF the re-
mainder. Fer example. all the conspic-
uous stars In orion have no sensible
parallax All we can say Is that they
must 30 many times as Tar away as
Sirius or Procyon-how many times We
do not know. But # follows that they
must be really much brighter than Sir
ius. which II transported TO so great a
distance would at best be ineonspieu-
Gus to the naked eye.
The Planets.
Mercury is morning star until the
18th. but evening star before his passage
through superior conjunction on that
date. He is too near the sun TO be seen
Venus is evening star. and is also very
near the sun. though she may perhaps be
visible at the end Of the month. when
she sets half an hoar -!ter sunset
Mars is morning star in Virgo, and Is
now rapidly gaining brightness. On the
22d he is in quadrature with the sun. and
crosses the meridian at s g. ID. He Is
at his greatest phase, and appears
through the telescope ike the moon
three DAYS from the full
Jupiter is evening star in Capricornus,
setting about 500 p. 70.
Saturn Is evening star in SagittaTius,
setting at about Z >. m
Uranus is In conjunction with the sun
on the 18th. and is invisible.
Neptune is in opposition on the 9th
His position on the LIST is in right as
censiCn 6 hours u minutes 40 seconds,
and declinati0n % degrees Is minutes p
seconds north. while on the 31st IL is
right ascension 5 hours minutes Z sec
onds. and declination p degrees Il min
utes - seconds north He can be seen
with a small telescope. though it takes
a large one TO show his disc. His green
color viii aid in finding him. though ne
can 0aly be certainly identified By his
motion
The Moon.
First quarter occurs at 1 a m. on the
Sth. full moon al II p. N. on the 18th.
last quarter az p. N. on the 21st, and
new moon at p. m. on the 18th. The
moon IS nearest US on the 18th. and
farthcst away on the %. and again on
the 29th. She Is il conjunction with Sa-
turn on the Sd. Jupiter on the 5th. Nep-
tune on the 18th. Mars on the 21st, Ur-
anus on the 2Sth and Venus and Mer-
curry on the 30th. On the 18th she oc-
cults the fourth magnitude star Delta
Tauri and two smaller ones near It. The
occulation lasts from 6:55 TO 1883 p
m. as seer from Washington. and should
De interesting 20 watch with glass.