Everything in the universe is in constant motion.

The Wanderers
The word planet is derived from Greek and means 'wandering star'. Thousands of years ago, humans were trying to decipher what they saw in the sky. Known as the five wandering stars, the planets intrigued early star gazers. They asked themselves what propelled these celestial bodies across the sky. Today we know that planets orbit the Sun on the ecliptic- the plane of the Solar System- and cross over several constellations in the background, known as the Zodiac constellations.

Five of the nine planets in the solar system are visible to the naked eye: Mercury, Venus, Mars, Jupiter and Saturn, all of them as bright as, and often much brighter than, first magnitude stars. Uranus and Neptune may be viewed with a good pair of binoculars. Only Pluto requires the use of a 15-cm or larger telescope. Mercury is rarely seen because its tight elliptical orbit keeps it close to the Sun, and it is visible only for a few weeks of the year.

Lunar Cycle
From the phases of the Moon, we are most familiar with the monthly revolution, or orbit, of this natural satellite around our planet. One lunar cycle takes 29 ½ days to complete. A "new" Moon is the point at which the Moon is between the Earth and the Sun. The first quarter is approximately 7 days into the cycle; a full moon occurs at 14 or 15 days; and the last quarter falls at the 22^nd day point in the Moon's orbit around Earth. The timing of a number of celebrations in different religions, including Passover and Easter, are dependent on the lunar cycle.

Do the Stars Move?
At different times of the night, a person at any one location on the Earth views different sections of the sky. The sky as a whole appears to be moving! What creates this 'apparent' motion of the stars and constellations? In fact, it is the Earth that is moving, rotating on its axis from west to east once every 24 hours, and revolving around the Sun once every year.

At the North Pole, all of the stars seem to move in giant circles around Polaris. These stars do not rise or set, so they are said to be circumpolar. Though we can see these stars all year long, their positions in the sky change depending on the season and time of night.

At the Equator, the sky moves very differently than it does at the North Pole. At the equator, the North Star can be found on the horizon. Everything is still moving around it, but here the stars rise in the East and set in the West.

In Canada, most places where people live have a combination of the two extremes. We see circumpolar stars in the North and stars that rise and set in the other parts of the sky. This means that we can see different stars in the East, South, and West of the sky depending upon the season of the year and the time of night. Since the stars in the North are circumpolar, we see these stars all year long, but their positions in the sky change with the seasons and time.

This motion of the stars can be captured by anyone with a camera that takes time exposures. The resulting star-trails will resemble those that are so prominent in the Gemini Observatory.

Why do the stars we see change from season to season?
The Earth's annual orbit around the Sun, one Earth year or 365 ¼ days, results in dramatic changes in the stars visible from any one point on the planet. As the position of the Earth changes with the seasons, different constellations come into view. For example, Orion is not visible from May through July, but the circumpolar Big Dipper is visible year round although its position changes in the sky.

Try the planisphere activity on this site to identify the stars and constellations that are visible at different times of the year in Canada.

Comets
Known as 'dirty snowballs', comets are composed of ice thought to be left over from the formation of the solar system. Those that revolve around the Sun in elliptical paths sometimes take hundreds, or thousands, of years to complete one orbit.

As a comet approaches the inner solar system, the Sun's warmth vaporizes (sublimates) the cometary ice. This creates a huge cloud of gas and dust that is pushed back into a classic cometary tail. There are actually two types of tails-a white dust tail and a blue gas or plasma tail- which always point away from the Sun.

Comet Hale – Bopp, one of astronomy's more famous comets, was visible in Canadian skies during the spring of 1997.