Uranus and Neptune are Bigger Than The Moon, Too

August is a slow month for observing the planets.

Jupiter is still observable low in the southwest at dusk, and remains up for a few hours, though it’s low in the sky and past its prime. It’s been a great Jupiter year (even if I never did manage to see that darned Red Spot Junior) -- there’s been lots of detail to watch in the bands and festoons.

There are lots of double shadow and moon transits on Jupiter this month, too. A shadow transit is when the shadow of one of Jupiter’s four largest “Galilean” moons falls on the planet as we see it from Earth. They’re fairly easy to see even when Jupiter is low in the sky, even with a small telescope -- I’ve seen them using the club’s 60mm loaner refractor. The Galilean moons move fast: It only takes a few hours for one of their shadows to cross Jupiter’s disk. So you can watch ingress (when the shadow first appears) to egress (when it disappears off the other side), and in many cases you’ll also get to watch the moon that’s casting the shadow cross in front of Jupiter, where it will eventually disappear against the planet’s brightness.

But they’re usually visible for a while against the limb of Jupiter before they disappear, and if you haven’t seen that, it’s an eerie sight every astronomer should see at least once.

But really, this month is best for the outer planets. Neptune is at opposition on August 11th, and is very well placed for observing. Look for it in Capricornus. Uranus, too (in Ophiuchus) is well placed for observing. And Pluto is just a few months past opposition, so this is still prime Pluto season: grab a good chart and a big scope and go at it.

Mercury emerges into morning twilight early in the month, but is lost again by mid-month. Venus, too, is in the morning sky, and makes a close pass with Mercury on the 10th, and a very close pass with Saturn (which is only visible during the latter half of the month) on the 26th and 27th.

Mars is too close to the sun to be easily observed right now. That’s ironic, because it looks like the annual flood of “Mars will be BIGGER THAN THE MOON!” hoax emails has begun to flow (inspired by the conjunction three years ago, but people never put dates or details on stuff they forward around the internet, do they?) I talked about this hoax in last August’s column, while we were all getting ready for the Mars opposition. It didn’t occur to me at the time that I’d see it again, even in years like this one that don’t have a Mars opposition at all; but I guess this may become an annual event.

Oh, you were wondering about the title of this column? Well, last year when the hoax mails were flying, people kept asking me “Is Mars going to be bigger than the moon?” The answer to that is, of course Mars is bigger than the moon. And Uranus and Neptune -- well, they’re WAY bigger than our little moon. In fact, all the planets except Pluto are bigger than our moon. So if someone asks you if Mars is going to be bigger than the moon this August ... the answer is yes! It just won’t LOOK bigger ...