[GreenKeys] OT: Beauty in the sky tonight... from NASA...

[Don Robert House]

February 26, 2009:  Be careful, this sort of thing can cause an  
accident.

On Friday evening, Feb. 27th, the 10% crescent Moon will glide by Venus,

forming a gorgeous and mesmerizing pair of lights in the sunset sky.

Moon-Venus conjunctions are not unusual, but this conjunction has some

special qualities:



(1) Venus is at maximum brightness: magnitude -4.6. The planet is twenty

  times brighter than Sirius, the brightest star in the sky. It is so  
luminous that

it can actually shine through thin clouds and cast subtle shadows on  
the ground.

Right: A Moon-Venus conjunction in Dec. 2008 photographed by Tamas  
Ladanyi

  of Mönichkirchen, Austria. This month's conjunction will be even  
tighter and

brighter.



(2) As seen from North America, the Moon-Venus separation is only a  
little

more than 1o. Stick up your thumb and hold it out at arm's length. Venus

and the Moon will fit comfortably behind the thumb-tip.

Tight conjunctions like this are the most beautiful of all.



(3) Not only is the Moon a crescent, but so is Venus. A small telescope
pointed at the glittering planet will reveal a slender 20%-illuminated  
disk.
Add it all together and you've got a major distraction. Evening  
drivers should

pull to the verge. Staring at Venus and the Moon could be riskier than  
texting!

Venus is a crescent because, like the Moon, it has phases. The planet  
can be

  be full, gibbous, new, or anything in between. The illuminated  
fraction we see

  on any given date depends on how much of Venus' nightside is turned  
toward

Earth.



It might seem odd that Venus is brightest now when it is a crescent.

That reverses our commonsense experience with the Moon, which is  
brightest

when it is full. A 6-month animation of Venus created by Hong Kong

astrophotographer "Wah!" solves the mystery at a glance:

The crescent phase of Venus occurs when Venus is close to Earth, very  
big and

bright. The full phase of Venus, on the other hand, occurs when Venus  
is on the

opposite side of the Sun, far away and relatively dim.

Crescent Venus is so bright, you can see it in broad daylight. During  
the day on

Friday, scan the sky for the crescent Moon. Hint: Stand in the shadow  
of a tall

building to block the glare of the Sun. At noon, the Moon will be due  
east of the

Sun's position. Got it? Look a few thumb-widths around the Moon and— 
voilà!

Venus pops out of the blue. The planet is surprisingly easy to see  
when you

  know where to look.



Once daytime Venus has been located, you might feel tempted to examine

the planet with binoculars or a telescope. Don't. The nearby Sun can  
damage

your eyes if you accidentally point your optics in that direction.

Wait until the Sun sets and behold the pair framed by deepening  
twilight blue,

first with your unaided eyes, then with a small telescope. On the  
Moon, you

will see mountains, craters, and a vast expanse of nighttime lunar  
terrain

gently illuminated by Earthshine. On Venus, you will see a delicate  
little

crescent of impenetrable clouds.

It's a nice way to end the day.