March 19, 2011

Sheer Lunacy!


You’ve probably heard the media hype about the “giant” full Moon this weekend. It is true that the Moon will reach full phase today, at 2:10pm EDT to be exact. It is also true that, coincidentally, lunar perigee, the Moon’s nearest approach to Earth for 2011 will occur less than an hour later.

The Moon’s orbit is slightly elliptical so its distance from Earth varies by 10% from about 450,000 km to 500,000 km at apogee. A variation of about 35,000 miles. I’ve heard silly reports in the media to the effect that the Moon will appear 15% larger and 20% brighter. Don’t believe it.

Luna will appear about 1-2% larger in diameter. The difference will be so slight you couldn’t tell the difference if you compared images of this month’s full Moon and February’s or April’s. So Saturday’s full Moon will be special for the reasons I’ve outlined above, but I doubt you’ll be able to tell the difference.

What is significant about this full Moon is that we can expect especially high tides and, possibly, earthquakes? Remember, at full lunar phase the Moon and Sun are on opposite sides of the Earth. At full phase gravity makes Earth bulge a bit around the equator. This, for me, is the significant factor. In late February when I was reviewing astronomical events for the month of March the thought occurred to me the nearest lunar perigee in 18 years at a full Moon might portend earth temblors. Then Japan happened.

At any rate, enjoy the full Moon but don’t expect it to hit your eye “like a big pizza pie”. If friends, neighbors or family call, write or email about the “giant” Moon, tell ‘em its SHEER LUNACY and you know it because you read it here!

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March 17, 2011

Mercury/Jupiter update

I was having dinner with my friend Li on Wednesday evening at about 8:45 I suddenly realized the sky was clear for the first time in what seems like a year. We were in the Bashford Manor area in Louisville. Li, his nephew and I ventured outside at 8:50pm to take a look.

Once we were outdoors I was a little disappointed thinking the planets had set. There was a tree stand to the west of us about where I thought the sunset and ecliptic should be. We moved around for a minute or two and then Li spotted the two of them in an open space between the trees and the glare from an excessively lit parking lot.

Mercury was about 8 degrees above and right of Jupiter. What really surprised me is how bright Mercury is. Both planets are naked eye with Jupiter being about 1 magnitude brighter than Mercury. Contrary to my earlier posting the best time to catch this planetary pair will be between about 8:30 and 9:00 pm local time. Mercury will climb higher each night until reaching maximum eastern elongation on Monday, March 22nd. Don’t miss Mercury’s best showing of 2011.

Here is a link to an image taken by my friend Duke Marsh of the LAS

Clear skies, Mark the StarGeezer

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March 10, 2011

Mr. Mercury, meet Mr. Jupiter

Mercury will make his best evening appearance of the year during the next couple of weeks. The tiny planet will reach maximum “eastern elongation” (angular separation from the Sun) on March 22nd. That evening little Mercury will set about 45 minutes after the Sun.


Mercury and Venus are “inferior” planets, that is they are between us and the Sun. Therefore they always appear in our sky within a couple of hours of sunrise or sunset. This best evening appearance of speedy little Mercury for 2011 will be made all the more interesting by a conjunction with Jupiter. Beginning this weekend Mercury will climb higher in the sky each evening.

This chart was prepared using John Walker’s Your Sky. It shows the view to the western horizon Tuesday evening, March 15th.

On March 15th our speedy little friend will appear a couple of degrees to the right (north) of big old Jupiter. Although the two planets will appear to be very close to each other they’ll actually be about 600 million miles apart. It’s celestial smoke and mirrors.

You will need binoculars to spot reddish orange Mercury. Start watching for him this weekend about a half hour after sunset low in the evening twilight to the west. You will need binoculars for this. Then watch from evening to evening as Mercury leaps up past Jupiter. The Jovian one will soon be lost near the Sun, he sets a few minutes earlier each evening. Enjoy the show.

Before the change to Daylight time take a look around 6:45 pm local time. Once we’re on Daylight time try this around 7:45 pm. This chart was prepared using John Walker’s Your Sky.

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March 1, 2011

See Venus in Daylight!

There’s an old doo-wop song called “Venus in Bluejeans”. This morning I’m updating the lyric to “Venus in Daytime”

This will be a good chance to log a daytime viewing of the brilliant planet Venus. The crescent moon will be about 4 degrees (half a fist width at arms length) below and left of Venus. Look for them near sunrise, about 6:45 am local time Tuesday morning March 1st, in the southeast.


Remember the distance and position of the two, and then later in the morning (in full daylight) scan the same area (to the right and up slightly from the Moon’s crescent) with binoculars, and you should be able to pick out Venus.  If you have the time, you can look every 15 minutes or so, from sunrise on, to keep a fix on the Moon, which will be dimming.

Be extremely careful and avoid looking directly at the Sun naked eye or through optics. You can permanently blind yourself in less than one second.

Wednesday and Thursday try to spot the very slim crescent waning Moon. “New” Moon is Friday, March 4th. Luna will glide into the evening sky this weekend as the next lunation begins. Saturday evening March 5th the new crescent Moon will appear just west (right) of Mercury and Sunday near Jupiter. Mercury will make its best evening appearance of the year March 13-16.

Map prepared with John Walker’s Your Sky planetarium program

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