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In our outlook we soon observe that we do not by our revolution
come to see the same stars rise at the same hour every night. Orion
and the Pleiades, our familiar friends in the winter heavens, are
gone from the summer sky. Have they fled, or are we turned from
them? This is easily understood from Fig. 42.

When the observer on the earth at A looks into the midnight sky
he sees the stars at E; but as the earth passes on to B, he sees
those stars at E three minutes sooner every night; and at midnight
the stars at F are over his head. Thus in a year, by going around
the sun, we have every star of the celestial dome in our midnight
sky. We see also how the sun appears among the successive
constellations. When we are at A, we see the sun among the stars
at G; but as we move toward B, the sun appears to move toward H.
If we had observed the sun rise on the 20th of August, 1876, we
should have seen it rise a little before Regulus, and a little
south of it, in such a relation as circle 1 is to the star in Fig.
43. By sunset the earth had moved enough to make the sun appear
to be at circle 2, and by the next morning at circle 3, at which
time Regulus would rise before the sun. Thus the earth's motion
seems to make the sun traverse a regular circle among the stars
once a year: but it is not the sun that moves.

[Illustration: Fig. 43.]

There are certain stars that have such irregular, uncertain, vagarious
ways that they were called vagabonds, or planets, by the early
astronomers. Here is the path of Jupiter in the year 1866 (Fig.