Wiccans see the Divine as being a part of nature; in our belief system, celestial objects have certain sacred meanings and representations.
"Wondrous lady of the Moon
You who greets the dusk with silvered kisses;
Mistress of the night and of all magics,
who rides the clouds in blackened skies
and spills light upon the cold Earth;
O Lunar Goddess,
Crescent-One,
Shadow maker and shadow breaker;
Revealer of mysteries past and present;
Puller of seas and ruler of women;
All-wise Lunar Mother,
I greet Your celestial jewel
at the waxing of its powers
With a rite in Your honor.
I pray by the Moon,
I pray by the Moon,
I pray by the Moon."
--Wiccan Prayer, by Scott Cunningham
The Moon is viewed by Wiccans as a symbol of the Goddess, with its three phases: waxing (when the cresent Moon is growing in size), full (when the Moon is completely round), and waning (when the crescent Moon is getting smaller). Because of the three phases, it is associated with the Triple Goddess, whose aspects are Maiden, Mother, and Crone.
The waxing moon is the time when Wiccans do rituals for things to grow, to come into being; for example, a Wiccan might choose the time of the waxing moon to do a ritual for love or for wealth. The waxing moon represents the Maiden aspect of the Triple Goddess.
The Full Moon, representing the Mother aspect of the Triple Goddess, is an Esbat, or minor holiday, and it is a time to honor the Goddess and to do rituals for things that have been building to come to fruitition. It is a sacred time and a time of completion. The Full Moon adds power to any spell done at this time. The Mother aspect of the Goddess is especially protective of mothers and children.
The waning moon, representing the Crone aspect of the Triple Goddess, is the time for banishing rituals, rituals to break the hold of a bad habit or a drug. Rituals for justice can also be done at this time.
The New Moon, the time when the Moon is completely dark and cannot be seen in the sky, is the time for rituals of beginning and ending. It is a good time for protective rituals, although almost any ritual can be done on this day--much like the Full Moon, which lends power to any spell done on that day.
Lunar Deities:
To Wiccans, the Sun represents the God. The rebirth and the peak of the Sun consitute two of the major holidays of Wicca--the Winter Solstice and the Summer Solstice. He is the fiery Sun, filled with the fire of life and excitement. The Sun also meant the difference between life and death to some cultures, when if you didn't have a stockpile of food to last you the winter, it meant you--and possibly all your tribe/clan/family-- might die. That meant that the later Winter came, the earlier Spring came, and the better the growing season, all of which relate to the Sun, the more likely you were to survive.
Solar Deities:
The stars have long been associated with mystical things; in the Tarot deck, the Star (a Major Arcana card) is a symbol of good things. Many early religions stated that the dead walked among the stars. Stars are also associated with astrology, something that has become more popular with the advent of New Age stuff.
Some pages with information about the Moon:
The Current Moon Phase--or Moon phases for other times. Totally cool. Check it out!
The Old Farmer's Almanac--has some of the most complete information about moon phases and everything related to the moon (sun, eclipses, everything).
(Tip: the moon is waxing if, when you draw a straight line across the two ends, it forms a b; if it forms a d, the moon is waning. I remember it by saying, "Brigit is waxing; Diana is waning.")