Every couple of years, Mars suddenly becomes the brightest orange star in the sky, and newcomers ask why it is not always that impressive. The answer is opposition — a predictable event in the clockwork of the solar system.

Opposition happens when Earth passes directly between Mars and the Sun. On that night, Mars rises at sunset, is visible all night, and sets at sunrise — and it is also when Mars is closest to Earth.

The roughly two-year-and-two-month gap comes from orbital periods. Earth takes one year to circle the Sun; Mars takes about 687 days. Earth laps Mars the way a faster runner laps a slower one on a track.

Not all oppositions are equal, because Mars's orbit is noticeably elliptical. When opposition coincides with Mars being near perihelion, its closest point to the Sun, the planets come much closer together, and Mars appears dramatically larger.

Plan around the window, not the single night. The best observing extends for several weeks on either side of opposition, when Mars is still large and bright. Mark the date in advance and use the weeks before it to practise.

On a good opposition night with a modest telescope, expect a small but clearly round orange disc, a white polar cap, and, on nights of steady air, dark markings such as Syrtis Major rotating across the disc over successive evenings.