Page:Astronomy for Everybody.djvu/64

The real diurnal motion is the turning of the earth on its axis.

The apparent diurnal motion is that which the stars appear to have in consequence of the earth's rotation.

The real annual motion is that of the earth round the sun.

The apparent annual motion is that of the sun around the celestial sphere among the stars.

By the real diurnal motion the plane of our horizon is carried past the sun or a star.

We then say that the sun or star rises or sets, as the case may be.

About March twenty-first of every year the plane of the earth's equator passes from the north to the south of the sun, and about September twenty-first it repasses toward the north.

We then say that the sun crosses to the north of the equator in March, and to the south in September.

In June of every year the plane of the earth's equator is at the greatest distance south of the sun, and in December at the greatest distance north.

We say in the first case that the sun is at the northern solstice, and in the second that it is at the southern solstice.

The earth's axis is tipped twenty-three and a half degrees from the perpendicular to the earth's orbit.

The apparent result is that the ecliptic is inclined twenty-three and a half degrees to the celestial equator.

During June and the other summer months the northern hemisphere of the earth is tipped toward the sun.