April 16, 2010

Have a nice dose of Mercury (the good kind)

Filed under: Astronomy — geezerwriter @ 10:54 pm

Last night (April 15) i happened to pass by our west-facing patio door just before 9PM and saw that the afternoon clouds had gone, and a delicate, slim crescent moon and a brilliant evening star were the only heavenly bodies visible. I assumed, with hardly any thought, that the evening star was Venus, as usual.

At first I managed to simply admire the sight for its own sake, but soon the geek in me revved up and I remembered that I had recently downloaded an iPod App called “Star Walk”. (I usually just get the free ones but I had coughed up the princely sum of $3 for this one after reading a recommendation.) I draws a graphic representation of the sky at any time, night or day, on any date, past or future, potentially replacing a lot of star charts.

I had gotten the app on a whim – I’ve had an interest in astronomy, on the most amateur of levels, since I was about ten years old. It would be hard to find a place less nurturant of that pastime: we lived about 13 miles north of downtown Chicago, with all it lights and pollution, and our immediate neighborhood had lots of tall trees (this was before Dutch Elm Disease). If you went down to the shore of Lake Michigan you could get a fine view of the eastern and northern skies, but the south was hopeless. When I was a bit older I would be able travel after dark the two miles to the Dearborn Observatory on the Northwestern University campus, but at first I was limited to my backyard and a small neighborhood park a block away.

I still remember how excited I was one June evening when I found my “first” star and constellation. I had learned the really basic things  that every kid gets, like the Dippers and the Pole Star, but on this night, after studying my little star chart, I let the curve of the handle of the the Big Dipper lead my eye to the kite-shaped constellation called Boötes and the brilliant gleam of Arcturus, the first magnitude star at the base of the kite’s tail. I can still pick out most of those constellations that are high in the spring and summer skies – anything south of the celestial equator is pretty much a mystery to me, though. Thanks, Chicago.

Thursday at 9:00

But enough of that. As I looked at the evening display I remembered Star Walk and fetched my iPod. I spun the app around to the west (apparently with an iPhone’s fancy accelerometer and such, that wouldn’t be necessary: it just KNOWS which way you are looking.) and sure enough, there were icons for Venus and the Moon and OMG that’s Mercury!

Mercury is the only one of the planets that can be observed without a telescope that I had never seen. It is a shy little bugger. It is very small, smaller than anything in the solar system except Pluto (which doesn’t really even count as a planet any more, they say) and much, much smaller than Venus; and its orbit is very close to the Sun, which means that it is only above the horizon for a short time just before the Sun rises or just after it sets. And of course at those times the sky is very bright and little Mercury is easily overwhelmed. Not to mention that when we are looking at things which are near the horizon, we are looking sideways through the atmosphere and looking through a lot more clouds and airborne muck and crud than when we are looking directly overhead.

I stepped outside and looked as hard as I could but couldn’t see anything but Venus and the Moon. So I fetched my good binoculars and there it was: a tiny but steadily glowing dot just about to drop behind the treetops. (The trees are downhill from our house, so their tops are near the horizon.) I then tried to get a photo, but didn’t think I had time to set up my tripod (just finding it could easily take until sunrise) so I just put my hope in the camera’s image stabilizer. Venus and the Moon showed up pretty nicely, but I didn’t really expect to get a usable picture of Mercury.

Venus, the Moon and maybe Mercury

But this morning I took a little time with iPhoto and adjusted the levels on the sharpest of the pictures and there was a tiny white dot below and a bit to the right of the Moon, right among the treetops. It is possible that the dot is just an artifact of the photo processing software, but it is right where it I remember seeing Mercury, and it has about the right brightness level, compared to that of Venus. You probably can’t see it on the little image to the left, but if you click on it you can see the full size image. If your software setup allows you to view the image at full size (about four times as big as your whole computer screen) you might be able to see it.

Friday at Sunset

Star Walk shows that the relationship between the Sun, Venus and Mercury will not change very quickly over the next few days. The Moon will quickly scoot up higher above the horizon, getting brighter each day (Boo!) but further away (Yay!) but the planets will move much more slowly. I’m talking about the apparent motion from our point of view – the planets are zipping right along in their orbits but the Moon is so much closer (a quarter million miles away versus about 93 million for Mercury) that it appears to travel proportionately faster. The second screenshot shows the relative positions of the bodies at sunset on Friday. You’ll notice that the Moon has moved quite a bit away from the horizon (after all, it has to get all the way around the sky and back in just 28 days) but the positions of the planets and the Sun haven’t changed much. If we get another clear sunset soon and you have a good set of binoculars, you might get a look at Mercury.

[I should point out, if it is not already clear from comparing the photo with the Thursday screenshot, that the icons used by Star Walk for the various bodies are not to scale.They are enormous when compared to the distances between the objects, so ignore their size and just use them for positioning.]

Mars & Saturn visiting Leo

And there’s more! If you act now you can see a near planetary grand slam, since all of the visible planets (except Jupiter) are now above the horizon at a civilized time of day. The last Star Walk screenshot shows a view of the southern sky at about sunset on Monday. About midway between the horizon and the zenith, you can see Mars and Saturn on either side of the constellation Leo on a line with the Moon. (Actually Saturn is in Virgo and Mars is in Cancer, but those constellations are rather faint compared to the prominent sickle shape that represents the shoulders and head of the Lion.) There is no rush to see these two, since they are much further away than Venus and Mercury and their apparent motion correspondingly slower. And having the Moon nearby might help you find them: they are very bright and much, much closer than the stars, so the brightness of the Moon will tend to wash out the stars and make these reddish planets stand out even more.

But wait! There’s still more! If you want to try for the quintifecta, the full grand slam, just stay up until dawn and move to a view of the eastern horizon (if such a thing exists around here – you may have to climb a mountain) and catch Jupiter playing the Morning Star role, rising just ahead of the Sun.

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