Before we answer this question, let's spend a little time on "blue moons." Tonight's (Friday) full moon is the second full moon this month (at least in the Eastern Time Zone). According to the modern definition, it's a "blue moon" since it's the second full moon in a given month. The next "blue moon" won't occur until July 2004.

However, according to the Maine Farmer's Almanac, a "blue moon" was referred to as the 3rd full moon in a season having 4 full moons. Think of it this way. Each of the 4 seasons has 3 months, and usually there will be 3 full moons - each of these 12 moons was assigned a name. For example, the full moon nearest the time of the equinox is called the "harvest moon." This usually occurs in September but can occur in October. But, when a season has 4 full moons, there's no name for the extra moon, and it became known as a "blue moon." The 3rd full moon and not the 4th is called a "blue moon" since only then will the names of the other full moons fall at the proper times. Using the above, tonight's full moon is not a "blue moon." So based on the Maine Farmer's Almanac definition, the next "blue moon" will occur next November.

It's possible that the moon can actually appear bluish. This only happens when smoke particles from burning fires or other atmospheric particulates scatter the moon's light in such a way that it looks kind of blue.

Now, for this week's question. If you happen to be visiting a place north of the Arctic Circle (66 1/2 degree north latitude) during December and January, you won't catch much more than just a glimpse of the Sun. This is because the Sun will be directly over the Tropic of Capricorn (23 1/2 degrees south latitude) on about December 21. If you're on the Tropic of Capricorn on this day at noon, the Sun will be at its zenith - its highest point in the sky ( 90 degrees from the horizon). So, from a village north of the Arctic Circle, the Sun will be below the horizon all day. 66 1/2 + 23 1/2 = 90 (see, science isn't so hard). The point is, you can't see an object (discounting refraction) if it's more than 90 degrees from your local zenith.

Although the moon and the Sun aren't always in the sky at the same time, they lie pretty much in the same plane. From the mid latitudes, weather permitting, we can always see the Sun and moon except, of course, when the moon's in the new phase. The shape of the moon changes from day to day, and it's position in the sky changes on a daily basis as well. However, where it is in the sky, isn't usually as obvious as how it looks.

Each year, the Sun ranges between a declination of 23 1/2 degrees north and 23 1/2 degrees south as it circles the sky. The moon goes through a similar up and down motion, but every month. Actually, the moon ranges a bit further north and south than does the Sun (a little over 5 degrees further north and south). On a seasonal time frame, the full moon assumes a place in the sky where the Sun will be 6 months hence. In other words, in mid winter, the full moon is high in the sky at midnight, like the Sun in summer at noon. Conversely, the full moon in summer is much lower in the sky. Thus, during winter, the moon illuminates the Earth at a much higher incidence angle than does the Sun. For instance, at 45 degrees north latitude, the midday Sun is approximately 22 degrees (2 fists held at arm's length) above the southern horizon on December 21. Whereas, the full moon at midnight on the date of the winter solstice is about 68 degrees above the southern horizon.

At about 75 degrees north latitude, in Resolute, Canada for example, the Sun and moon are both about 38 degrees above the horizon at their maximum elevation. The key is that the Sun reaches its zenith in June, and the moon reaches its zenith in December. If the Moon is full on December 21, it'll be pretty close to being directly over the Tropic of Cancer (23 1/2 degrees north latitude). Therefore, it'll be up all day (24 hours), as is the Sun in summer. What this means is that, even though the Sun is long gone in mid winter, Mr. Moon is still there for you. It works out pretty good really, in mid summer when the Sun is up all day anyway, the moon takes a siesta, and in mid winter, when the Sun heads south for a little R&R, the cold moon at least provides a little light.

By the way, not only will there be a "blue moon" this Friday (30th), but for everywhere in the eastern and southern U.S., the moon will occult Saturn. This occurs when one celestial object of an apparent larger diameter (the moon) obscures another (Saturn). Most skygazers consider this to be a rare event. Shortly after sunset, as the moon rises, Saturn appears a degree (2 moon diameters) to its left. As the pair climbs the eastern sky, the moon's orbital motion draws it in front of the "ringed planet" and blocks our view for a time. Because the leading edge of the moon is bright, Saturn's disappearance is more easily observed through binoculars or a telescope. For more about the moon see: http://www.netaxs.com/~mhmyers/moon.tn.html
and the Earth and Moon Viewer: http://www.fourmilab.ch/earthview/vplanet.html
Also see today's Earth Science Picture of the Day: http://epod.usra.edu/