Summer officially begins at 10:04 tonight.

As the Earth moves around the sun, its axis always points to the same place in the sky, but the relationship of the Earth to the sun constantly changes.

The North Pole is tilted toward the sun for half of the year and tilted away from the sun for the other half.

The solstices are those brief points in time at which the sun is at its greatest distance north (summer solstice) or south (winter solstice). The term solstice may be used more generally to mean a culminating point or turning point.

Most of us hardly give the solstices a glance. Preindustrial agricultural societies followed the seasons closely, using the sky for their timekeeping and calendar reckoning.

Ancient observers also spent a lot of time studying the sun's position in the sky from day to day.

The sun is so bright during the day that it blots out the background stars, making it difficult to track.

Those early observers accurately estimated the sun's position by observing the sky just before sunrise and just after sunset, which gave them a good estimate of where the sun was with respect to the starry background.

Technically, all the stars we see in the night sky are moving with respect to the solar system, but they are so far away their movements appear tiny and take many years to detect with sophisticated instruments.

Moon Watch

The moon is in a waxing (growing larger) gibbous (more than half-lit) phase, becoming full on Sunday.

Contact Tim Hunter at skyspy@azstarnet.com