August 2003 Close Approach
The information below was provided by author and astronomer Jeffrey Bennett.
A number of you have already asked about the upcoming "close encounter" with Mars, so I've checked into the story behind it. Here's the basic facts in Q&A format:
- Is it true that this will be the closest pass of Mars in 60,000 years? Yes. Based on calculations of planetary orbits, it appears that on August 27 of this year, Mars will be closer to Earth than it has been at any time since 57,538 BC, which is just shy of 60,000 years ago.
- So is this really "the best opportunity to observe Mars in 60,000 years"? Technically yes, but in reality Mars passes almost as close to Earth about every 15-17 years, and the difference between this pass and other close passes is too little to really notice.
- Will the close pass affect Earth? Remember that "close" is a relative term. Mars will pass 55.758 million kilometers (34.6 million miles) from Earth. That's still roughly 150 times farther away than the Moon. Other than being bright in the sky, this close pass of Mars will not have any effect on Earth whatsoever. (For example, the tidal effect of Mars at this distance is roughly a million times weaker than the tidal effect we feel from the Moon.)
- Is it worth observing? Sure! Even if other close passes are just about as good, they come almost two decades apart. So this will be one of a handful of "best" opportunities to view Mars in your lifetime.
- How do I go about viewing Mars? If you go out on a clear night right now,
you can't miss it - Mars is the bright red object in your sky. Viewing will
remain good through September, peaking on the August 27 close pass date.
If you want to observe Mars through a small telescope, check out this article
from Sky and Telescope: S&T Article
That covers the basics. For those of you wondering why Mars is passing unusually close to Earth, here's a brief explanation:
Fact #1: All planetary orbits around the Sun are elliptical, which means they have a closest point to the Sun (called perihelion) and a farthest point from the Sun (called aphelion) on each orbit. For example, Earth is closest to the Sun each year in early January, and farthest from the Sun each year in early July.
Fact #2: Planets closer to the Sun orbit faster than planets farther away, which means that Earth "passes by" Mars in its orbit at intervals of a little more than 2 years (roughly 26 months). Mars is at its brightest during this time when we are passing it by, because that is when it is directly opposite the Sun in our sky and nearer to us than at other points in its orbit. (Astronomers call these close passes "opposition" because Mars is opposite the Sun in our sky.)
Now put Facts 1 and 2 together: Mars has a "close pass" about once every 2 years,
but a close pass will be especially close if it happens when Mars is at the closest
point in its orbit around the Sun rather than at some other point in its orbit. T
hese especially close passes occur about every 15-17 years.
Why is this close pass even closer than others? Two reasons:
(1) this close pass happens to be occurring when Earth is near the far point of its orbit
and Mars is right at the closest point in its orbit, whereas other close passes are typically
off a little more from these orbital positions;
(2) over many millennia, the near-point of
Mars orbit has actually been getting slightly nearer to the Sun, as a result of gravitational
tugs by other planets (mainly by Jupiter). The two factors conspire to give us the closest
approach since 57,538 BC, according to calculations by Aldo Vitagliano of the University
of Naples, Italy. For details, see this article from Sky and Telescope:
S&T Article