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Considering Copernicus

Dave North


Gumby has to look up to see the Moon, and he'll have a pretty good chance since the weather is getting better



Copernicus, Copernicus, Copernicus. All Dave talks about is Copernicus.

Big honking crater in the middle of the Moon. So what?

So look for yourself.

No better time. In April, the Moon will be highest in the sky near First Quarter (this year, the 19th). Copernicus appears just after, in this case the 21st.

Gumby has to look up to see the Moon, and he'll have a pretty good chance since the weather is getting better.

And for convenience freaks, the Moon will be darn near zenith (best time to view) right at sunset. With darkness squandering time now in effect, you should be able to squeek through the rat race, stuff down some food pellets and get out into the back yard just about in time - then see the whole show before Sixty Minutes starts (is that still on?)

Some months, you only get half of Copernicus one night, then you have to wait until the next night to see the rest (usually such things happen on an every-other-month basis, because the Moon circles us - from our point of view - about every 29-1/2 days. Do the math).

But no April Fools this month: the whole thing will be nicely placed near the terminator when you start observing.

If you don't have a map, don't worry: you'll have no problem finding it. Look for the great big showy crater just a hair above center top to bottom.

Yeah, that's it all right.

Next you'll want to take up the magnification about as far as the sky will bear. If we're lucky, that will be quite a bit. Sometimes we get incredible seeing in April, and there is that elevation (less air) thing going for us too.

But if it doesn't turn out that way, don't despair. Even a mere 125x is enough to give a satisfying (if not overly detailed) view of what we're hunting.

What, by the way, are we hunting? Everything.

If there's something interesting on the Moon, a good example of it can be found in the area of Copernicus.

Reasonably, let's start with ... Copernicus! It's a hair shy of 60 miles across (93km), which (if my map reading is at all good) means you could comfortably fit the San Francisco Bay Area into it (say, San Jose to Vallejo or so).

To get some idea of what you'll be looking at, I seriously suggest perusing and fooling around at for a few minutes. Photo of the Century! May well be.

Once you get to the eyepiece, I think you'll be surprised how much of this you can see yourself, and how much better the contrast will look. You'll never get the same level of detail Lunar Orbiter did, but you can get a prettier view.

For fun, compare your memory of those digital images to what you see. Then go back and look again. I think you'll be surprised.

But the crater itself is just the beginning.

Next, travel about one crater diameter antiterminatorward and look for a sprinkling of little dots. They should be quite distinct.

Those are a cluster of secondary impacts, the landing zone of junk thrown out of the crater when the big bang happened. This is probably the finest secondary field on the Moon.

Next, look north of the crater about one diameter (a bit less) and just before you get to Montes Carpatus (the Carpathians) you should see a little dark line pointing to a flattish crater in the mountains.

The crater is Gay Lussac, and the line is a rille (rima) named after the crater (which is in turn named after a French physical chemist of some renown).

Good mountains, no?

Then if you wander south nearly two Copernicus diameters and start heading toward the terminator, you'll see a very distinct crater about half the diameter of our subject (this smaller crater is named Reinhold, after a German astronomer) and continue to the terminator, you might catch sight of a little dome.

If my terminator numbers are right, the astounding dome field surrounding Hortensius is probably just over the line into the dark - bleeding into view around 10pm and pretty much good by 11. However, the Moon will be sinking by then, and the seeing likely feeble.

But don't despair: I usually get these numbers wrong and maybe they'll show in time. (Domes are basically shield volcanos, like Maunas Loa or Kea that principally form Hawaii).

So, what did we have, mountains, detailed craters, secondaries, rilles, domes ... oh I forgot rays! Copernicus has a very distinct and crowded ray system, but that won't really start to show for another few days.

Darn. If you really want to see it all, you'll have to look tomorrow night, and a few nights more.

And that's just for one crater.


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