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The Shallow Sky

Is Mars as Large as the Moon? You Bet!

Akkana Peck

A really good Mars opposition. Photo courtesy of Akkana Peck and NASA/STSci.


Mars, rising a bit before 11pm, is starting to brighten and grow noticeably. It's still small (13 arc-seconds at month's end, about 2/3 the size of Saturn's disk without the rings) but dedicated late-night Mars observers should be able to pick out some detail on the planet.

There's been some misinformation about Mars floating around the internet for the past few months about the amazing close pass Mars is supposedly making this August. Usually, they begin with THE RED PLANET IS ABOUT TO BE SPECTACULAR, and end NOONE ALIVE TOADY (sic) WILL EVER SEE THIS AGAIN!!!

Longtime Mars observers will immediately see what's going on. The LAST Mars opposition, in August 2003, was in fact the closest opposition in 73,000 years, or 59,604 years, or various other big intervals depending on who ran the numbers. It was also problematical because Mars was quite far south and therefore low in the sky unless you took a trip south to see it. Those factors combined to make a Mars opposition which was quite good, and a lot of fun, but really nothing that special. This year's (at the end of October) may well be better even though Mars isn't that close.

But apparently a few months ago someone stumbled on a two-year-old announcement, failed to notice the year, forwarded it, and now garbled versions are all over the net.

The really interesting part is that there's much more misinformation about the 2003 opposition this time than there was in 2003 when it was actually happening.

The latest variant is along these lines:


I puzzled over that one for some time. Of course Mars is quite a bit bigger than our moon: about twice as big in diameter, in fact. But the

query was obviously about apparent size as viewed from earth. Why would anyone claim Mars' apparent size would ever be comparable to the

moon's? As I got more inquiries quoting different versions of the message, I gradually saw what had happened.

It turns out that one version of the email had a sentence like this:

[blah blah] At a modest 75 power magnification, Mars will look as large as the moon to the naked eye. [blah blah]

But somewhere along the way, the message got garbled, and became:

[blah blah] At a modest 75 power magnification.

Mars will look as large as the moon to the naked eye. [blah blah]

The second half of the sentence, out of context, became the beginning of a new paragraph, and suddenly people are imagining a huge Mars

looming over their local cityscape.

It's an interesting lesson in information diffusion. And also a lesson in, "Don't believe everything you read on the internet." Including this column. Unless you're reading this on paper, in which case you should take every word as gospel.

So. If a huge moon-sized Mars isn't going to be in our sky this August, what WILL there be to look at?

Mercury gradually moves into the morning sky as August progresses, and should be observable for all but the first week of the month, showing a waxing crescent phase.

Venus, in the early evening sky, is drawing closer to the sun and will become more difficult to observe later in the month. On the evening of the 7th, it makes a very close pass with a slim crescent moon. We'll miss the occultation here (you'd have to go to Alaska or the Yukon to see that), but the close pass should be a lovely sight here. Try to catch them as early in twilight as you can - is it easier to find bright Venus, or the larger but much dimmer crescent moon? Then watch them as they set: they'll draw closer together as they sink lower in the sky.

Jupiter is very low in the western sky. Going ... going ... gone! Catch ya next time! Meanwhile, Saturn begins to emerge out of the sun's glare into the morning sky.

Neptune is at opposition on August 8, relatively low in the southern sky in Capricornus. At magnitude 7.8 it's visible in binoculars, but you'll probably need fairly good star hopping skills. It's easier in a telescope, with enough magnification to distinguish its small 2.3 arc-second blue-green disk from the stars around it. Try star hopping at 75-100x if you don't find it searching with lower powers.

Uranus, in Aquarius, won't reach opposition until next month, but its larger 3.7" disk and brighter 5.7 magnitude make it a much easier target, theoretically visible to the naked eye and a relatively easy binocular target. A telescope will show a nice disk.

Pluto, in Ophiuchus, is still fairly well placed for evening observing. It's already past the meridian by the time the sky gets completely dark, and since it's fairly far south it's only 40 degrees up, but that should still be enough for ambitious Plutocrats.

Around midnight on the night of August 25-26, the third quarter moon skims past the southern edge of the Pleiades, M45. Most star clusters would probably disappear next to a moon this bright, but the Pleiades are bright enough that I bet they'll hold their own. Check it out!


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