Close Encounters of the Martian Kind: Mars Opposition 2003, Why will Mars appear so large this opposition?

"I dare not affirm that I am able to observe the phases of Mars; nonetheless, if I am not mistaken, I believe I have seen that it is not perfectly round."
-- Galileo Galilei, in a letter to Benedetto Castelli, December 30, 1610

We've talked about what an opposition is, but what you might not know is that not all oppositions are the same, some are better than others. Obviously when a planet is close to us it appears larger, so the planet's distance from us plays a big factor in how good an opposition will be.

This illustration shows how large or small Mars can appear depending on its distance from Earth.

Just to illustrate how much distance matters, when Mars is at conjunction, opposite the Sun from Earth, it is over five times farther from us than when Mars is at opposition. During this time, Mars is very small. Even larger telescopes will not show much detail at that time.

The least favorite opposition, called an unfavorable opposition, is when Mars is at aphelion. Aphelion is the point in a planet's orbit when it is farthest from the Sun. Viewing will be better than when Mars is close to conjunction, but again, it will be hard to see any details in small telescopes.

So the best time to view Mars is when the planet is at opposition and closest to the Sun. That is what is happening in August 2003. But there is another reason why this opposition is even more special and why Mars will appear still larger than during other Martian perihelion and oppositions. It has to do with Earth's orbit.

Like Mars, Earth's orbit is not circular, but it is only about one-sixth as elliptical as Mars' orbit. This means that the distance between Earth and the Sun and planets also varies. On July 4, 2003 Earth was at aphelion and this makes Earth farthest from the Sun and closer than usual to Mars.

When you combine all these facts, Mars at opposition and perihelion and the Earth at aphelion, it makes for terrific views of Mars! All of these things have not happened so close together for over 73,000 years.

Close Encounters of the Martian Kind

What is an opposition?

Why will Mars be larger than usual and this event so rare?

Where and When to see Mars!

Timeline for Mars in 2003/2004 - What to Look for on the Red Planet!

Close Encounters of a Red Kind: Retrograde Motion of Mars

Mars through a Telescope: Getting the Most from the Red Planet

The Martian Sky: Stargazing from the Red Planet

More about Mars the planet

Constellations

The Solar System