Page:Popular Astronomy - Airy - 1881.djvu/131

From Wikisource
Jump to navigation Jump to search
This page has been validated.
LECTURE IV.
117

LECTURE IV.

Recapitulation of Lecture III.—General notions on Parallax.—Method of finding the Moon's Parallax and Distance.—Methods of finding the Sun's Parallax by Transits of Venus across the Sun's Disc.—Causes of failure of other methods.


IN the course of the present lecture I shall depart completely from that part of astronomical observation with which we have been engaged for some time, relating to the apparent motion of the heavens; and in leaving this part of the subject, I shall remark, as I have done before, that there is nothing of so much importance as that you should know the stars and the apparent diurnal motion of the heavenly bodies yourselves; and for this purpose the thing that you should have is a celestial globe. Every person who wishes to know anything of Astronomy should become acquainted with the principal constellations, so as to be able to recognize them at sight in the heavens; to observe their diurnal motion, and the difference in the appearances of the stars at different seasons of the year. This is of the greatest importance, in order to give you an idea of the apparent motion of the sun and planets among the stars.

There are two particular subjects which I have omitted to mention so fully as I would have wished, but I will now allude to them finally. The first is this. In treating of the apparent motion of the sun among the stars. I pointed out to you that it appears to describe a path through the stars which is inclined