The Earth is rotating around an axis
(called its rotational axis). Some objects rotate about a
horizontal axis, like a rolling log. Some objects, such as a skater,
rotate about a vertical axis. The Earth's axis is tipped over about
23.5° from vertical.
How do we define up and down in space? What would "vertical" mean? For the Earth, we can think of vertical as straight up and down with respect to the plane (called the ecliptic) in which the Earth orbits the Sun.
Earth's rotational axis always points in the same direction, so that the North Pole points towards the star Polaris. Think of the Earth as a spinning top, tipped over to one side.
The Earth rotates around once in 24 hours - that's a rate of 1000 miles per hour!. The time it takes for the Earth to rotate completely around once is what we call a day. It's Earth's rotation that gives us night and day.
The combined effect of the Earth's tilt and its orbital motion result
in the seasons.
The source of this material is Windows to the Universe, at http://www.windows.ucar.edu/ at the University Corporation for Atmospheric Research (UCAR). ©1995-1999, 2000 The Regents of the University of Michigan; ©2000-01 University Corporation for Atmospheric Research. All Rights Reserved. Site policies and disclaimer