Check Out Two Magic Planets Before Dawn.

 Our Winter is a good time to relax, sleep late, enjoy a break from school or work.  Waking before sunrise is just not done. This week is a little different. 

To find out why, set your alarm for dawn. (Although it describes the morning sky from the USA ‘s Winter most of the above video iss till relevant for Australia.) Every morning this July, the two brightest planets in the solar system will put on a show before sunrise.  Look out any east-facing window to see Venus and Jupiter, shining side by side, so close together you can hide them behind your outstretched palm.  It’s a great way to start the day.

On the 4th of July, Venus will be passing dead-center through the Hyades cluster, a loose grouping of stars 153 light years from Earth.   Using binoculars, scan around the bright planet; you’ll see dozens of stars scattered across the velvety-black sky. The temporary addition of Venus will make it seem that a supernova has gone off in the cluster.

Three mornings later, on July 7th, Venus and Jupiter line up with Aldebaran, the bright red eye of Taurus the Bull.  Aldebaran is a red giant star of first magnitude.  Together with Venus and Jupiter, it forms an almost perfect vertical line in the brightening dawn sky.

This amazing shot was taken by Shevill Mathers  this  morning, July 4,  from his  Southern Cross Observatory Tasmania.

The best, however, is yet to come. On July 9th, Venus and Aldebaran converge to form an eye catching planet-star pair.  Scarcely more than a degree of arc will separate the two celestial bodies as Jupiter looks down from overhead. 

And then, on July 15th, a 12% crescent Moon joins the show, forming a bright celestial triangle with Venus and Jupiter.

The slender arms of the crescent cradle a ghostly image of the full Moon.  That’s caused by Earthshine, sunlight reflected from our own planet onto the otherwise dark lunar landscape.

A crescent Moon with Earthshine is considered to be one of the prettiest sights in the heavens.  A crescent Moon with Earthshine plus Venus and Jupiter–that’s worth waking up for even in the middle of an Aussie Winter.

 

The Da Vinci Glow

When you think of Leonardo Da Vinci, you probably think of the Mona Lisa or 16th-century submarines or, maybe, a certain suspenseful novel. That’s old school. From now on, think of the Moon.

Little-known to most, one of Leonardo’s finest works is not a painting or an invention, but rather something from astronomy: He solved the ancient riddle of Earthshine.

You can see Earthshine whenever there’s a crescent Moon on the horizon at sunset. Look between the horns of the crescent for a ghostly image of the full Moon. That’s Earthshine.

For thousands of years, humans marveled at the beauty of this “ashen glow,” or “the old Moon in the new Moon’s arms.” But what was it? No one knew until the 16th century when Leonardo figured it out.

In 2005, post-Apollo, the answer must seem obvious. When the sun sets on the Moon, it gets dark–but not completely dark. There’s still a source of light in the sky: Earth. Our own planet lights up the lunar night 50 times brighter than a full Moon, producing the ashen glow.

Visualizing this in the 1500s required a wild kind of imagination. No one had ever been to the Moon and looked “up” at Earth. Most people didn’t even know that Earth orbited the sun. (Copernicus’ sun-centered theory of the solar system wasn’t published until 1543, twenty-four years after Leonardo died.)

Wild imagination was one thing Leonardo had in abundance. His notebooks are filled with sketches of flying machines, army tanks, scuba gear and other fantastic devices centuries ahead of their time. He even designed a robot: an armored knight that could sit up, wave its arms, and move its head while opening and closing an anatomically correct jaw.

To Leonardo, Earthshine was an appealing riddle. As an artist, he was keenly interested in light and shadow. As a mathematician and engineer, he was fond of geometry. All that remained was a trip to the Moon. It was a mental journey:

In Leonardo’s Codex Leicester, circa 1510, there is a page entitled “Of the Moon: No Solid Body is Lighter than Air.” He states his belief that the Moon has an atmosphere and oceans. The Moon was a fine reflector of light, Leonardo believed, because it was covered with so much water. As for the “ghostly glow,” he explained, that was due to sunlight bouncing off Earth’s oceans and, in turn, hitting the Moon.

Right: Leonardo made this sketch of a crescent moon with Earthshine. It appears in the Codex Leicester. [More]

He was wrong about two things:

First, the Moon has no oceans. When Apollo 11 astronauts landed at the Sea of Tranquility, they stepped out onto rock. Lunar “seas” are made of ancient hardened lava, not water.

Second, Earth’s oceans are not the primary source of Earthshine. Clouds are. Earth shines because it reflects sunlight, and clouds do most of the reflecting. When Apollo astronauts looked at Earth, the oceans were dark and the clouds were bright.

But these are quibbles. Leonardo understood the basics well enough.

Above: A picture of Earth taken by Apollo 11 astronauts. From the Moon, Earth is 4 times wider than the sun and about 50 times brighter than a full Moon. [More]

In the decades ahead, humans are going to travel in person where Leonardo’s imagination went 500 years ago. NASA plans to send astronauts back to the Moon no later than the year 2018. Unlike Apollo astronauts, who stayed for a few days at most, these new explorers will remain on the Moon for weeks and months. In the process, they’ll experience something Apollo astronauts never did: nightfall. A lunar “day” is 29.5 Earth-days long: about 15 Earth-days of light, followed by 15 Earth-days of darkness. Apollo astronauts always landed in daylight and took off again before sunset. Because of the bright sun, they never saw the soft glow of Earthshine at their feet. But the next generation of astronauts will.

And just maybe, on a late-night stroll behind the outpost, guided by the soft light of Earth, one of them will bend over and scratch something in the moondust:

“Leonardo was here.” Source: NASA

Related articles

• The Mystery of Venus’ Ashen Light (universetoday.com)
• What is the shiniest thing in the solar system? [Space] (io9.com)