ASTRONOMY. 
solute length both to the earth and moon, 
though very different as to the number of 
days; we having 365-.' natural days, and 
the Lunarians only 12^, every day and 
night in the moon being as long as 29| on 
the earth. 
Mars is not so bright as Venus, nor even 
as Jupiter, though nearer to the sun. Its 
colour is a little reddish. Some spots have 
been observed upon its surface, from which 
its rotation round its axis, and the inclina- 
tion of its axis to the plane of its orbit, 
have been determined. This planet some- 
times appears gibbous, but never horned, 
like the moon, which shews that his orbit 
includes that of the earth, and that he shines 
by a borrowed light. 
Ceres Ferdinandea is a very small planet, 
situated next without Mars: it was dis- 
covered on the first day of the present cen- 
tury by Mr. Piazzi, an Italian astronomer. 
Pallas is another very small planet, dis- 
covered by Dr. Olbers of Bremen, on the 
28th of March, 1802. Two others have 
also been discovered, one by M. Harding, 
and the other by a pupil of Dr. Olbers. 
To these have been given the names of 
Juno and Vesta. These planets Dr. Hers- 
chel proposes to call asteroids, because they 
are so much smaller than any of the other 
planets. 
Jupiter is the brightest planet next to 
Venus. When viewed by a telescope, seve- 
ral belts are observed across its disc, paral- 
lel to its equator : these belts are variable, 
and are supposed to be ranges of clouds in 
the atmosphere of the planet. Jupiter is 
surrounded by four moons of different sizes, 
which move about it in different times. 
These moons are sometimes eclipsed by the 
shadow of Jupiter falling upon them ; and the 
eclipses have been found of great use in de- 
termining the longitudes of different places 
on the earth : Ex. Suppose two observers of 
an eclipse, one at London, the other at the 
Cape of Good Hope, the eclipse will ap- 
pear at the same instant of time to both ; 
but being situated under different meri- 
dians, they count different hours, according 
to which the difference of their longitude is 
found. Thus, if an emersion of a satellite is 
observed at London 9 h 33' 12", and at an- 
other place 10 h 46' 45", the difference of 
time is l h 13 33 ', of course that other place 
is 18° 23' 15 ' east of London. 
The eclipses of Jupiter’s satellites have 
been applied also to measure tire velocity of 
light : by comparing the times of the appa- 
rent entrance and emersion of the satellites 
with tables calculated for the mean dis- 
tances of the earth from the satellite, the vi- 
sible emersion at the least distance is found 
to happen about eight minutes sooner ; and 
at the greatest distance about eight minutes 
later than the tables : consequently a ray of 
light is about 16 minutes in passing through 
the earth’s orbit, or eight minutes in 
coming from the sun to the earth. If 
therefore the distance be 95,000,000 of 
miles, the velocity of light per second is 
cqua! to =198 thousand miles in 
8X60 
a second nearly. 
Saturn can hardly be seen by the naked 
eye. When examined by a telescope, it 
exhibits a very remarkable appearance. It 
is surrounded by a thin, flat, broad lumi- 
nous ring, which surrounds the body of the 
planet, but does not touch it. This ring 
casts a strong shadow upon the planet, and 
is divided into two, by a distinct line in the 
middle of its breadth. The rings are circular, 
but appear elliptical from being viewed ob- 
liquely. 
According to Dr. Herschel, the dimen- 
sions of the rings, and the space between, are 
as follows : 
Miles. 
Inner diameter of the smaller ring 146,345 
Outside diameter of ditto 184,393 
Inner diameter of the larger ring. . 190,248 
Outside diameter of ditto 204,883 
Breadth of the inner ring 20,000 
Ditto outer ring 7,200 
Ditto of vacant space,.. 2,839 
Besides this ring, Saturn has seven moons 
of different sizes, and its body is surrounded 
also by belts, like those of Jupiter. 
The Herschel planet, with its six satel- 
lites, have been entirely discovered by Dr. 
Herschel. It cannot be seen without a te- 
lescope, hut it does not require a powerful 
one. The satellites cannot be seen with- 
out the most powerful telescopes. We shall 
subjoin in the opposite page a table which 
will contain a number of particulars relating 
to the planets, that will be found of great 
utility to the reader. 
