Evening star., 1897-04-03

1t are above the Horizon April 4. at PM.
position of this star is scarcely, if at all,
affected by this movement of the earth
Let us figure a little on the probable size
of a sun which at this unmeasurabie dis
tance is yet one Of the brightest stars in
the armament.
An IncOncefvable Distance.
The best photometric measurements make
the brilliancy of Arcturus about one-fifth
| Of that of Sirius. 1t has been estimated
hat Sirius shines with j light equal to the
sombined light of forty--soIne say seventy
! suns placed side by side at its distance from
US. Hence the combined light of eight suns
ITO adopt the smallest CT the numbers just
giVen) set side by side at the distance of
Sirius would form for us star of the bril-
nancy OF Arcturus. At ooube that distance
1t would require four times as many suns
10 form a star which would be equally
bright; at three times that distance the
NUMBER OF suns must be nine times as
great; at four times the distance. sixteen
| Tunes as great, and on, the number con-
tlnually increasing with the square of the
| distance. The distance of Sirius is now put
! at about nine light years. that is to say
| it takes the light Of this star flashing
through space at the rate of lS6ao0 miles a
second. nine years to make the passage
| from 1t to us. The Ieas. distance which il
has been thought be assigned to Arc
turus, upon the basis of DIR. Elkin's obser-
Vations, is sixty-seven light years, with a
| probability that it is much greater than
| this. Astronomers now speak indeed of
Arcturus as in all likelihood 100 or even 900
ilght years distant from us. Let US be
moderate and say NINETY; or. in other
| words, assume as probGble that Arcturus
Is ten times as far from US as Sirius. The
| square of 10 is 1oo and this multiplied by $
gives 500 as the number Of suns which must
| be SET side by side at the distance of Arc
turus to make star equal TO it in splendor.
1t can readily be figured out that a single
sun to present disc equal in to the
| combined disc of these 500 must have a
| diameter early 2S times as great as the
sun 5; and in that case il equal in
| volume over 20,0;0 suns. The steps by
which these figures have been reached have
! been purposely given. for the result of the
| ejaculation is so astounding as almost TO
| take away ones breath. Allowance must
| be made, of course for a wide margin of
error. But when the most liberal allowance
/ has been made there still remains the GER
| tainty that Arcturus surpasses the in
volume several thousand times. Our sun re-
moved to its distance would most certainly
become Invisible to the naked eye.
The Planets.
| Mercury was in Superior conjunction'
| with the sun. or directly behind the sun, on
| the 1st of the month Since that date 1t
| has been evening star, though it has not
! yet come into visibility. In week or SO
| from today it should be so far out of the
| [" lllSnI glow as 10 become visible ndlI
! or three-quarters of an hour after sunset
| low in the west. 1t will continue to be vfsi-
| BILE during the remainder of the month.
| reaching its greatest angular distance from
! the Sun-about tWenty-one Gegrees-on the
18th.
There is j popular notion that Mercury is
| a very difficult object to see. This Is a mis-
| take due probably to the circumstance that
much of our Information in astronomical
| matters has been derived from the books of
English writer's. 1t is true that in the high
| latitude of England owing to the great in
| cIination of the eciptic with respect TO the
horizon. this planet can be seen well only
| at certain seasons Of the year, when the
| conditions are most favorable. But in the
lower mean latitude of the United States
| Mercury can be seen by one who knows
! when and where to look for IL whenever 1t
is near it's greatest distance from the sun,
either east or west. The average duration
of the time of it's visibility in the latitude Of
| Washington is about two weeks.
| Venus shcne with her greatest brili;ancy
! as an evening star on the 21St OF last mon b.
| She is rapidly drawing in toward the sun.
| and by TIE middle of the month she will
be too the to be visible to the
naked eye. She will pass between us and
| the sun-will be in inferior conjunction
on the 2Sth. After that date she will be a
morning star for the rest of the year.
Mars is still an evening star, in the con-
stellation Gemini, at about two-thirds of
| the distance from Aldebaran to PolluN
| Though still equaling in brightness a star
| of the first magnitude. Mars has ceased to
| be an object Of special interest either to
! the naked-eye observer or the astronomer
Its distance from us now is nearly 140, ,OOO
coo miles.
Jupiter is now the reigning evening star.
| though his brilliancy has diminished some
what since the date of his opposition. Feb
| ruary % He is now in Leo. about three
| degrees east OF Regulus. Since December
| % Jupiter has been retrograding, or mov-
| irg westward. On the 25th of this month
| he will be stationary. After that date his
| movement will be direct, toward the
| east.
Saturn is now an evening star, rising at
| about 10 pm. IT is in the Scorpion, some 10
| degrees northwest of Antares. About two
| degrees farthe" in this direction is Uranu.;
| Neptune. never visible to the naked eve
| is III Taurus. between the horns.