Spring 1999  This new feature in our newsletter, inspired by the
questions we have received over the years from interested readers, will answer your
questions about astronomical issues. If you have a question about astronomy, please
forward it to us at mira@mira.org. |
Bruce Weaver: Both the location of sunrise and sunset and the location of the North Star are related to the orientation of the Earth’s rotational axis. As you know, globes representing the Earth are always mounted with a 23 ½ degree tilt. This is to represent the fact that the rotational axis of the Earth is tilted relative to its path around the Sun.The laws of physics say that this axis has to keep pointing in the same direction in the sky. That point in the sky is very near Polaris, the pole star. Thus, that star always appears to be in the same place in the sky, day and night, throughout the year. It is a different story for the Sun. At the summer solstice, around June 22, the north pole of the Earth is tilted toward the Sun. Thus, from the north pole, the Sun never seems to set. Somewhere in Canada (and Siberia), the Sun just sets for an hour or two before rising again. Even as far south as Monterey, the Sun rises north of east and sets north of west. As the year progresses, the Sun, as viewed from Monterey, rises and sets further south each day. At the equinox, about September 22, the Sun is directly over the equator and, for all parts of the Earth, the Sun rises directly in the east and sets in the west. Until the next equinox, in March, the Sun will rise and set south of east and west. To help visualize this, you may want to walk around a lamp with a globe. Keep the pole pointed in a fixed direction (north is most realistic). If you spin the globe you will see sunrise and sunset on the globe and, as you walk around the lamp (remember to keep the pole pointed at the same distant location, ignoring the location of the Sun) you will notice the effects of different illumination at different times of year such as summer and winter. |