ASTRONOMICAL NOTES. 595 
On the 17th at at iih. 59m. 00s., Europa is eclipsed and reappears. 
Following the same lines connecting Venus, Saturn and Jupiter, 15° farther 
east, we find Mars ; it is in the constellation Cancer, and will be in the evening 
twilight, in the northeast quarter of the heavens at an elevation of about 20*', 
and the same distance north of east. 
This is the fourth planet in order of distance from the Sun, and the next one 
outside the earth's orbit. Its mean distance from the Sun is about one hundred 
and forty-one millions of miles. It is easily recognized with the naked. eye when 
near its opposition, by its fiery red light. It is much more brilliant at some oppo- 
sitions than others, the present is not a very favorable one to see it, but yet it 
will exceed an ordinary star of the first magnitude. The variations of its bril- 
liancy arise from the eccentricity of its orbit, and consequent variations of its 
distance from the Earth and the Sun. 
Mars has been an interesting object of telescopic research from the fact that 
it is the planet which exhibits the greatest analogy with our Earth. The disk, 
even with a small telescope, can be seen to be divided into light and dark por- 
tions, which some observers suppose to be continents and oceans. Around each 
pole is a region of brilliant white, supposed to be snow. It must be said in favor of 
these suppositions, that if our Earth were viewed at the distance at which we view 
Mars, and with the same optical power, it would present a similar telescopic aspect. 
But it is also possible that if the optical power of our telescopes were so increased 
that we could see Mars as from a distance of a thousand miles, the resemblances 
would all vanish as completely as they did in the case of our Moon. This is the only 
planet besides the Earth of which we can be sure that the time of axial rotation 
admits of being determined with entire precision ; it has been found to be 24h. 
37m. 22.73s., this is correct within three or four hundredths of a second. The 
Equator is inclined to the plane of its orbit about 27°, so that the vicissitudes of 
the seasons are greater there than on the Earth in the proportion of 27° to 23^°. 
Owing to this great obliquity, we can sometimes see one pole of the planet, and 
sometimes the other, from the Earth. 
Comet Brooks, so closely identified with the one of 181 2 (i. e. Encke's) as 
to leave but little doubt that it is the same, was first observed September 3, 1883. 
It was then in the constellation Draco; it moved from this into Lyra, passing only 
a few degrees north of Vega in the latter part of November, it entered the Milky- 
Way and Cygnus, thence through the eastern edge of Vulpecala. On December 
29th it entered Pegasus, passing from this constellation into Pisces on the loth 
of January, and on the 15th it was on the boundary line between this and Aqua- 
rius, at this time it had attained its maximum brilliancy and was 118 times brighter 
than it was when discovered, and plainly visible to the naked eye. On the 2 2d 
of January it will enter Cetus, and by February ist will be in Sculptor; its bril- 
liancy will have faded about one-half; by the 12th it will be below the horizon all 
the time. The only time it will be possible to see it will be during the first week 
of the month, and a telescope or opera glass will be required. It will be nearly 
due southwest, and elevated from 10° to 15°. 
