10 June 2009

Eerie Moon

We all know what the Moon looks like when it is in its early phases, waxing from a thin crescent over a two-week interval of time through first quarter and then to full moon. Although many people might not be able to explain exactly which way the "horns" of a crescent moon are pointed, it's something that you just know is right when you see it. For us living in the Northern Hemisphere, the horns of the young crescent moon point left and up when you see the moon in the western sky after sunset. That is, they point primarily south (left) and up (east) because the moon is being illuminated by the setting sun -- which is typically to the lower right (northwest) of the crescent moon. If you suddenly saw the horns of the crescent moon pointing the other direction, you might find it strangely discomforting. I certainly would!

Each month as the moon wanes from full moon to last quarter to a thin crescent in the morning, the orientation of the crescent reverses compared to the first 14 days of the lunar cycle. But because these phases are visible late in the night and in the early morning, there are generally fewer opportunities to see the moon in these phases. When I am up late at night or very early before sunrise and I see an old moon in the sky, the reversal of the orientation of the horns always throws me off. This week and weekend if you are up late at night or early in the morning you can take note of this as the waning moon passes Jupiter (see image) and continues eastward in its path, slimming to a thin crescent by June 18-20. Sky and Telescope Magazine called the waning gibbous late at night an "eerie moon" and I can appreciate why they would call it that. Whenever you see the moon, be it a slender evening crescent just starting its 29-day cycle, or a bold full moon lighting up the night, or a waning gibbous, think about the view and how it makes you feel. If you can start to gain a familiarity with the phases of the moon, you will find it does indeed evoke different feelings depending upon which phase it is in.


Sidewalk Universe said...

I sure enjoy the waning phase cycle of our moon! I never tire of seeing it in our morning skies and it is the best time to do some serious observations of the Moon's interesting terrain. Besides early morning compilations before a busy day!

Hope you enjoy the remaining days of this cycle Paul!

Sidewalk Universe said...

Hey Paul, were you able to catch today's early 4 a.m. display of a beautiful receding Luna complete with earth shine along with Mars and Venus in tow? Wonderful!

Should be cool Saturday too with Luna being dragged by Mars and Venus.

I just open up my eastern facing bedroom window and enjoy the sights without leaving my comfy bed!

Are you planning on watching the Solstice sunrise/sunset tomorrow?

The Urban Astronomer said...

No view this morning - overcast skies over San Francisco. I will try again the next two mornings to catch the upcoming lineup of moon and planets. Summers in SF are that way ...