Astronomy Answers: Mars 2003

Astronomy Answers
Mars 2003

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From the middle of 2003 stories have been going around that something very special is going on with the planet Mars near the end of August. What is it?

At the end of August 2003, Mars is closest to the Earth (in its perigee) and directly opposite the Sun in the sky (in opposition). (These two phenomena are never very far apart.) It is not very remarkable by itself that Mars is in opposition and perigee, because this happens about every 26 months, but this time Mars gets closer than it has for thousands of years, though not that much closer that it merits a lot of brouhaha.

The Earth and Mars both revolve around the Sun in their respective orbits. Mars is on average about one and a half times as far from the Sun as the Earth is and therefore goes around the Sun slower than the Earth does. Every 26 months the Earth overtakes Mars, and then Mars is in its perigee and in opposition as well.

The orbits of Mars and the Earth are not perfect cirles but rather a bit oblong, and the center of each orbit is shifted away a bit from the Sun. This so-called eccentricity of the orbits (and especially of the orbit of Mars) causes the smallest distance between Mars and the Earth when the Earth overtakes Mars not to be the same every time.

When the Earth overtakes Mars in a region of space where their orbits are closer together, then the smallest distance between them will be smaller than average, and that is the case in August 2003. Such an extra-small distance occurs about every eighth opposition, or about once every 17 years.

The average smallest distance between Mars and the Earth is 78 million kilometers or 48 million miles (and the average greatest distance is 378 miljoen kilometers or 235 million miles), but that smallest distance can vary, because of the eccentricity, between about 56 million kilometers (35 million miles) and 101 million kilometers (63 million miles): that's a ratio of almost two. This time it is 56 million kilometers or 35 million miles.

It turns out that the smallest distance this time is the smallest since many thousands of years, but the difference with "normal" extra-small distances is itself small. As far as pictures or other observations are concerned, this opposition won't be noticeably different from other recent oppositions at an extra-small distance.

If Mars is closer than average, then it looks brighter and (in a telescope) bigger than average. Mars is now (mid-August 2003) much brighter in the sky than usual. However, this opposition of Mars is not equally well visible for everybody. We distinguish between observers in the arctic region (I, for example northern Canada), between the northern polar circle at 67° north latitude and the northern tropic at 23° north latitude (II, the northern temperate zone, for example central Europe), between the tropics (III, the tropics, for example Indonesia), between the southern tropic at 23° south latitude and the southern polar cirle at 67° southern latitude (IV, the southern temperate zone, for example South-Africa), and the antarctic region (V).

For observers north of the tropics (in zones I and II), Mars is in an unfavorable part of the ecliptic, so it doesn't get very high above the horizon there (and is not visible at all in the arctic region), loses more of its brightness to absorption of its light in the atmosphere of the Earth, and doesn't stay above the horizon for very long at night. In those respects, other recent extra-close oppositions were much better, though slightly less close.

For observers south of the tropics (zones IV and V), Mars is now in a favorable part of the ecliptic. There, Mars gets high in the sky and stays long above the horizon at night (it stays above the horizon all the time as seen from the antarctic region). For observers in the tropics (zone III), it does not matter in which part of the ecliptic Mars is.

Mars is now (August - September 2003) easy to spot. From the northern temperate zone (II, including the Netherlands and Belgium) Mars is the brighest "star" that you can see around midnight towards the south. In the tropics (zone III), look straight up around midnight. South of the tropics (zones IV and V), look towards the north around midnight.

Mars rises in the east (in the south east as seen from zone II, in the north east as seen from zone IV), moves towards the west, and then sets in the west (the south west as seen from zone II, the north west as seen from zone IV).

At the moment (mid-August 2003), Mars rises an hour or so after sunset and sets only after sunrise, but at the end of August Mars rises at sunset, and in September Mars is already up when the Sun sets. There are no bright stars in the region of the sky where Mars is, so it is almost impossible to miss.


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Last updated: 2021-07-19