We are in the home stretch of the historic 2003 close encounter with the planet Mars, which occurs officially at 5:51 a.m. ET on Wednesday, Aug. 27.

Earth has been approaching Mars ever since Aug. 10 of last year. At that time Mars was situated on the opposite side of the Sun at a distance of 248 million miles (400 million kilometers) from the Earth. When it finally emerged into the morning sky some weeks later, Mars was shining no brighter than a mundane second magnitude star.

But we have been slowly creeping up on Mars ever since, catching it on the inside of a celestial racetrack around the Sun.

The red planet now appears about 85 times brighter than when this orbital odyssey began and, on Aug. 27, it will be less than 35 million miles (56 million kilometers) away.

Each day until then, the proximity of the two worlds will rival a number of extreme close encounters that occurred in the past.

Myles Standish, who analyzes planetary orbits at NASAs Jet Propulsion Laboratory, recently compiled a list of the closest approaches of Mars to the Earth over a 6,000-year interval beginning in 3000 B.C.

From that list, SPACE.com has prepared a table of the top ten closest approaches of Mars to the Earth that have occurred since 3000 B.C. The table lists nine apparitions prior to 2003 in ascending order of rank.

A number of interesting conclusions are discussed below.

How to read the table

There is a long-term cycle of 79-years where the circumstances of any particular Mars opposition will replicate almost exactly. Our consciousness of this interesting periodicity is now quickened thanks to the above table, with the nine previous close encounters conveniently arranged for us.

Note how the 79-year cycle readily appears with the close approaches of 2003, 1924, 1845 and 1766, as well as with those of 1561, 1482 and 1403.

Incidentally, there exists an even longer (and more accurate) periodicity of 284 years, a cycle that that is also revealed in our table with the close approaches of 1924 and 1640, 1845 and 1561, 1766, 1482, 1198, and 1403 and 1119.

The question now beckons as to exactly how our 2003 Mars apparition would rate compared to those extreme close encounters dating back prior to 3000 B.C? Did the Red Planet come even closer than it is now?

In the 2003 Observers Handbook of the Royal Astronomical Society of Canada, Terence Dickinson wrote that 2003 would see "the nearest to Earth that Mars has been for approximately 100,000 years."

However, during the spring of 2002, Meeus asked Professor Aldo Vitagliano, an expert in celestial mechanics at the Universitá di Napoli Federico II in Naples, Italy, to check his result using numerical integration. Vitaglianos computation was rigorous to say the least: it took nearly three hours of number crunching on a Pentium 800-megahertz computer, taking into account the gravitational pull of not only all nine planets and our Moon, but the three largest asteroids (Ceres, Pallas and Juno) as well.

Vitagliano determined that the last Mars time that Mars was closer than this year occurred on September 12, 57,617 B.C., or 59,619 years ago.

In that year, Mars passed to within 34.622 million miles (55.718 million kilometers) of Earth, just a tad nearer than this years 34.646 million miles (55.758 kilometers).

"That's an interval ten times longer than all of recorded history," notes Francis Reddy, co-author of the book "Celestial Delights: The Best Astronomical Events Through 2010" (Celestial Arts, 2002). "The last time Mars came this close, Neanderthals flourished and humans had not yet occupied Australia."

Humans will not have to wait anywhere near as long as that for a Mars encounter as close, or closer than this year. In fact, using the earlier-mentioned 284-year cycle, we find that on Aug. 29, 2287, Mars will come 43,248 miles (69,601 kilometers) closer than in 2003.

Meeus explains that the reason for such a short interval until the next extreme close approach (as opposed to another 60,000-year wait), is that during recent millennia, the orbit of Mars has been gradually becoming more elongated thanks to the gravitational tug of the other planets.

As a consequence, Mars has been slowly getting closer to the Sun at the perihelion point of its orbit (that part of the orbit closest to the Sun), while getting farther from the Sun at the aphelion point of its orbit (that point of the orbit farthest from the Sun).

Lastly, take note of the intriguing fact that even though Standishs list extended all the way back to 3000 B.C., the Top 10 closest Mars approaches in our SPACE.com list appear "bunched together" between 1119 and 2003 A.D., within a relatively small interval of just 884 years. Such is likely an artifact of the perihelion point of Mars getting progressively smaller over thousands of years.

And because of this, Standish believes that our top ten list likely would stand the test of time; being valid not just for the past 5,000 years, but probably over the past tens of thousands of years as well.

We have provided the Mars-to-Earth distances for each case in both miles as well as in kilometers. Since the upcoming apparition will be the closest of all, the previous nine close encounters listed in the table will ultimately be surpassed during this week. Utilizing the U.S. Naval Observatorys Multiyear Interactive Computer Almanac (MICA), we have also been able to provide the dates and times when the Mars-to-Earth distance of a previous extremely close apparition will be matched in 2003.

As an example: Mars will match its second-closest approach to Earth (that of August 22, 1924) on August 26 at 01:53:47 UT (rounded off in our table to 1:54 UT). For North Americans, this corresponds to the calendar date of August 25 at 9:54 p.m. EDT, 8:54 p.m. CDT, 7:54 p.m. MDT and 6:54 p.m. PDT. Immediately thereafter, Mars will be closer to the Earth than it has been in modern recorded history. It will still be approaching our planet, however, finally arriving at its absolute closest point just under 32 hours later at 09:51:12 UT on August 27. (Mars will match the 1924 close-approach distance a second time as it recedes from Earth on August 28 at 17:46:09 UT).