Every once in a while, something will appear in the sky to attract the attention of even those who normally dont bother looking up. Its likely to be that way in the after-midnight hours of Wednesday night into early Thursday morning, July 16-17 when the Moon will appear very close to the now-brilliant planet Mars.

For a lucky few, the Moon will actually pass in front of the red planet.

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An opportunity to see the Moon occult a bright planet at night does not happen too often, so if you are fortunate to live in the occultation zone and the weather cooperates, this is a celestial event you won't want to miss.

Right now, Mars is becoming as spectacular as it can ever appear to us, as it is on target to make a historically close approach to Earth late next month. If you think Mars is dazzling now, consider that in just more than six weeks it will come closer to Earth than it has been in nearly 600 centuries. It will then glow 2-times brighter than it does now.

The northern limit of the occultation track runs roughly from near Fort Myers Beach in Lee County, northeast across the Florida peninsula to the community of Sebastian in Indian River County.

The track then continues out to sea over the open waters of the Atlantic and gently curves on a more north-northeast course, roughly a few hundred miles offshore from the U.S. East Coast.

Anyone south of this line will see a regular occultation; Mars becoming entirely hidden as the Moon passes in front of it. Those positioned north of this line, however, will see the Moon miss the planet entirely, barely passing just below it (an event called an appulse).

But for an observer fortuitously positioned exactly on, or immediately adjacent to that line its actually a narrow path about 26 miles wide the dark upper limb of the Moon will appear to literally graze Mars as it passes by. So within this path an unusual partial occultation should last about 10 to 15 minutes.

At its midpoint for those Floridians fortuitously situated along the southern edge of the path, the planets dazzling topaz disk may appear to disappear completely, then reappear intermittently in lunar valleys. In contrast, along the northern edge of the path, Mars southern edge will only briefly touch the limb of the Moon.

The Moon is a waning gibbous and is 85 percent illuminated. Because Mars is so bright this summer, the spectacular vanishing act can be watched with just your unaided eye or binoculars, although the very best views will certainly be afforded with a telescope.

According to David Dunham of the International Occultation Timing Association (IOTA), Floridians situated within about 80 miles south of the southern edge of the graze path will see Mars disappear and reappear from behind the Moons dark limb. Farther to the south Mars will disappear behind the Moons bright limb and reappear from behind the dark limb.

Owing to the relatively large angular size of Mars, the occultation will occur at a rather "leisurely" pace. From Miami, for instance, the Moons slow eastward drift will take about two minutes to completely cover, and later uncover the planets disk even longer for those to the north and closer in to the graze path, where the Moons limb will approach at even more of a slant.

Perhaps the best views will come when Mars slowly disappears and/or emerges from behind the Moons dark limb. Observers who have their telescopes trained at the right spot and who are looking at just the right moment will be able to watch, as the disk of Mars appears to slowly disappear and/or emerge into view from behind the dark lunar landscape.

The table below shows when Mars disappears and re-appears on July 17, 2003, for 16 selected cities in the United States, Caribbean, Latin America and Bermuda.

The table gives civil times (all a.m.) of Mars disappearance and reappearance from behind the Moon. Both the disappearance and reappearance of the planet can last up to two minutes. Disappearance and reappearance times are for Mars center. (T) Indicates that the event occurs during morning twilight. (D) Indicates that the event occurs in a daytime sky. Events without a (T) or (D) occur before the beginning of morning twilight in a completely dark sky, hence the time of local sunrise is omitted.

For the rest of North America, this will be a very close approach of the Moon to Mars (an even called a conjunction).

The Moon, moving around the Earth in an easterly direction at roughly its own diameter each hour will seem to creep slowly toward and ultimately pass just below the ochre planet. Even though most of North America will miss out on an occultation, Mars will command attention, as it slowly appears to glide above the Moon.

After closest approach, the Moon will move slowly away from Mars, with daylight arriving shortly thereafter in eastern areas. Most of the United States and Canada will be in darkness, or twilight at the moment that Moon and planet are closest together. The exception will be over the Maritimes of Eastern Canada, where it will happen after local sunrise.

SOURCE: Calculated exclusively for SPACE.com by Joe Rao