Backyard Astronomy: Mars, Fact and Fiction (2003-08-25)

By Cheryl Haimann

This week is the one Mars buffs have been waiting for. On Wednesday, Mars will be closer to Earth than it has been in almost 60,000 years. Whenever an astronomical event catches the attention of the mass media, as this one has, myths swirl around it like a nebula. We're going to set straight some of those misunderstandings.

Myth: Last night, I saw A) a satellite B) the International Space Station C) a comet D) a UFO E) a sign from God. Fact: Mars is visible in the southeast (moving to the southwest) and so bright that you would be hard-pressed to confuse it with a star. In fact, it is bright enough to be easily visible in city locations where few stars are visible, and so is easily misconstrued as something else. So for comments A through D, feel free to set the person straight. I would not presume to use science to prove or disprove comment E.

Myth: It couldn't have been Mars - it wasn't red. Fact: Mars appears red when it is low on the horizon because the light is refracted by Earth's atmosphere. When it is higher in the sky, it appears more yellow or orange. Compare this to the changing color of a full moon on the horizon compared to a full moon high overhead. For extra credit, compare Mars, rising in the southeast, to Antares setting in the southwest. Antares name, remember, means "not Mars" because the reddish color makes them easy to confuse - but not this year.

Myth: Mars hasn't been this close/this bright since the time of the Neanderthals. Fact: Technically true. However, Mars is at opposition (that is, on the opposite side of Earth from the sun) approximately every 18 months. Because the orbits of both Earth and Mars are elliptical, they are not always the same distance apart at opposition. Every 17 years or so, opposition occurs when Mars is at a near point. This year, it is just a bit nearer than it has been in the past. The difference in apparent size during a good opposition and a great one is barely recognizable. At its most distant, opposition occurs when Mars is twice as far away as it is now, and its apparent size is smaller.

Myth: Mars will be as bright as the moon on Wednesday. Fact: This is wrong on a couple of counts. First, to a backyard astronomer, Mars on Wednesday will not much different that it looked in July. Its brightness increased gradually as it neared Earth, and Wednesday's opposition will just be the peak, not a sudden burst of celestial fireworks.

Second, while Mars is bigger than the moon and just about as close as it ever gets, it is not THAT big or THAT close. Its diameter is only about twice that of the moon, and Mars is over 30 million miles from Earth, as opposed to the moon at 240,000 miles. Mars's apparent size will be just 1/72 the diameter of the moon. Mars would have to be less than a million miles from Earth to look as large as our moon.

But if you want to be nitpicky: Wednesday is a new moon, so on that night, Mars will indeed be brighter than the moon.

Myth: But Mars will look great through a telescope, right? Fact: That depends on what you mean by "great." Even at its best, Mars is small and far away. Astronomers are used to this, and recognize that it the planet's apparent size is larger than what they usually see. If you've never seen Mars in a telescope, though, you may be underwhelmed. It will not look like the photos from the Voyager surveys or the Hubble telescope. Imagine trying to see a quarter from two blocks away. That's what looking at Mars is like. Still, with the right equipment, you may be able to see the polar ice cap or some of the surface detail, assuming Earth's atmospheric conditions cooperate and a dust storm doesn't obscure Mars's surface.

If you mooch a view from a pal with a telescope, here's some advice. After you have looked at Mars, say, "What's your favorite deep sky object to look at this time of year?" Any friend worth having swing the scope around and show you a star cluster, nebula or galaxy, satisfaction guaranteed.