Comets are less common and much longer-lived than meteors, lasting usually for several weeks and may be visible for many months.

The appearances in the heavens have from earliest historic ages filled men with wonder and awe. Then they gradually became a source of questioning, and thinkers sought for explanations of the daily and nightly phenomena of sun, moon and stars.

We are still a long way off from being able to state with perfect confidence what the Corona is. It is certainly a complex phenomenon, and the various streamers which we see are not, as was at one time imagined, a simple manifestation of one radiant light. The true corona appears to be a triple phenomenon. First, there are the polar rays, nearly straight throughout their visible extent. Gradually, as these rays start out from points on the solar disc farther and farther removed from the poles, they acquire increasing curvature, and very probably extend into the equatorial regions.

If the earth is exactly at the node at the time of new moon, the moons shadow will fall centrally upon it and will produce an eclipse visible within the torrid zone, since this is that part of the earths surface nearest the plane of its orbit. If the earth is near but not at the node, the new moon will stand a little north or south of the plane of the earths orbit, and its shadow will strike the earth farther north or south than before, producing an eclipse in the temperate or frigid zones. Or the shadow may even pass entirely above or below the earth, producing no eclipse whatever, or at most a partial eclipse visible near the north or south pole.

Between the orbits of Mars and Jupiter there are scattered an untold number of small planets commonly known as asteroids or minor planets.

Around each of its poles appears a circular white patch, which visibly expands when winter prevails upon it, and rapidly contracts, sometimes almost completely disappearing, under a summer sun. From the time of Sir William Herschel the almost universal belief among astronomers has been that these gleaming polar patches on Mars are composed of snow and ice, like the similar glacial caps of the earth, and no one can look at them with a telescope and not feel the liveliest interest in the planet to which they belong, for they impart to it an appearance of likeness to our globe which is all but irresistible.

For two reasons Mars has generally been regarded as an older planet than the earth. The first reason is that, accepting Laplaces theory of the origin of the planetary system from a series of rings left off at the periphery of the contracting solar nebula, Mars must have come into existence earlier than the earth, because, being more distant from the center of the system, the ring from which it was formed would have been separated sooner than the terrestrial ring. The second reason is that Mars being less massive than the earth has run through its developments a cooling globe rapidly.

If the earth is exactly at the node at the time of new moon, the moons shadow will fall centrally upon it and will produce an eclipse visible within the torrid zone, since this is that part of the earths surface nearest the plane of its orbit.