Photograph by Nader Daoud, AP

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The planet Venus near a crescent moon. The two will share a close encounter on Sunday.

Photograph by Nader Daoud, AP

Sky-Watchers' Guide: Moon Joins Venus Sunday

Two brightest objects in evening skies join together.

Anyone looking west soon after the sun sets on Sunday, September 8, will be treated to a stunning close encounter between two of the brightest objects in the evening skies: the moon and the planet Venus.

In what's called a conjunction, the waxing crescent moon will pass very close to the planet Venus, with the closest approach occurring around 3 p.m. ET.

At that point the cosmic pair will be low and close together in the sky in the southeast, explained Ben Burress, staff astronomer at the Chabot Space and Science Center in Oakland, California.

"Daylight, however, will make seeing either of them difficult at best, so the best time to see them will be after sunset."

While this is an unusually close conjunction between the moon and a planet for most of the world, some lucky observers in parts of South America will witness Venus actually disappear behind the moon. (See a picture of a 2012 Venus-Jupiter conjunction.)

"If you are in Argentina or Chile or as far west as Easter Island, then you can observe the crescent moon get closer and closer to Venus until the planet winks out, for about an hour and a quarter, and finally winks back into the sky when it re-emerges from behind the moon," said Burress.

As an added bonus, on the following evening, September 9, the moon will rise higher in the southwestern sky and park itself to the far left of yellow-colored Saturn.

Through even the smallest telescope, the gas giant looks wondrous with its majestic rings and retinue of moons surrounding it.

Where and when is it best to spot this event?

For best viewing, Burress recommends finding a place with an unobstructed view of the low western horizon that's free of trees, buildings, mountains, and fog banks.

Begin searching for the conjunction about 20 to 30 minutes after local sunset.

But be quick since the pair will set about an hour and half after the sun does.

"Eventually you will notice the spark of Venus, followed by the graceful curve of the moon to its left," added Burress.

Look closely at the moon when the sky gets a bit darker at twilight—the unlit portion of the moon's disk will appear to be dimly visible thanks to light reflecting off Earth's oceans and clouds in an effect known as earthshine. (Test your solar system knowledge.)

What will the event look like in the sky?

The sky show will be quite impressive even with the unaided eye.

"The arc of the moon's lit crescent will be facing Venus, which will be a very bright and unmistakable flare of white," said Burress. (See video: Moon 101.)

"Sometimes the crescent moon can be difficult to see in the twilight unless you're looking right at it, so Venus, which is easy to spot, will guide your eye right to the spot."

The pair will appear to be closer to each other the farther east and south observers are located. Those on the east coast of North America will see the moon look less than 1.5 degrees from Venus—about the width of your thumb at arm's length.

From Europe, Venus will appear to be perched just above the moon.

Meanwhile, observers in Brazil, Argentina, and Uruguay will get to watch a lunar occultation around local sunset, in which the three-day-old moon hides Venus.

What if I miss this sky show?

In case you are clouded out, no need to fret—the moon often appears to join up with our planetary neighbors in the sky.

The next opportunity will be at dusk on November 6 and December 5, when the pair will appear close to each other and offer a great photo opportunity.

"Basically, the moon passes each and every planet every lunar month, though it generally isn't seen as close as on the September 8 conjunction, which is why this makes this one special," explained Burress.

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