Tonight, if the weather is clear, favorably placed skywatchers will have a view of one of nature's most beautiful spectacles: a total eclipse of the moon.
Earth's natural satellite will be immersed in the long, tapering cone of shadow cast out into space by the planet for a few overnight hours tonight (April 14) and into the wee hours of tomorrow morning (April 15). You can watch the lunar eclipse live on Space.com, courtesy of NASA, the Slooh community telescope and the Virtual Telescope Project.
This will be the first total lunar eclipse of 2014. Unlike a total eclipse of the sun, which often requires a long journey to the path of totality, an eclipse of the moon can usually be observed from one's own backyard. The passage of the moon through the Earth's shadow is equally visible from all places within the hemisphere where the moon is above the horizon. [How to Watch Tonight's Total Lunar Eclipse]
The total phase of the eclipse will be visible across all of North and South America, as well as Hawaii and New Zealand — a potential viewing audience of nearly 1 billion people. This will be the first opportunity from any place on Earth to see the moon undergo a total eclipse in 28 months.
The moon is expected to take 3 hours and 44 minutes to pass completely through the Earth's dark shadow, called the umbra. The total phase of the eclipse will last 78 minutes, beginning at 3:06 a.m. EDT or 12:06 a.m. PDT (0706 GMT) on April 15.
At the moment of mid-totality (3:46 a.m. EDT/12:36 a.m. PDT), the moon will stand directly overhead from a point in the South Pacific Ocean about 1,900 miles (3,000 kilometers) southwest of the Galapagos Islands.
Color and brightness in question
During totality, although the moon will be immersed in Earth's shadow, it likely will not disappear from sight. Rather, the moon should appear to turn a coppery red, a change caused by Earth's atmosphere bending or refracting sunlight into the shadow.
Since Earth's shadow is cone-shaped and extends out into space for some 857,000 miles (1,379,000 km), sunlight will be strained through a sort of "double sunset," all around the rim of the planet, into its shadow, and then onto the moon.
That isn't always the case, however. If a major volcanic eruption takes place in the weeks and months beforea total lunar eclipse, a cloud of ash and dust floating high above Earth could make the moon appear darker than usual during totality. Parts of the moon might even become black and invisible. This happened with eclipses in 1963, 1982 and 1992, which occurred soon after the volcanic eruptions of Mount Agung on Bali, El Chichón in Mexico and Mount Pinatubo in the Philippines, respectively.
Eclipse viewers can attempt to estimate the brightness and color of the moon during the upcoming lunar eclipse. ['Blood Moons' Explained: What Causes a Lunar Eclipse Tetrad? (Infographic)]
A careful description of the colors seen on the totally eclipsed moon and their changes is valuable. The hues depend on the optical equipment used, usually appearing more vivid with the naked eye than in telescopes. The French astronomer, André Danjon introduced the following five-point scale of lunar luminosity ("L") to classify eclipses:
- L = 0: Very dark eclipse, moon almost invisible, especially in mid-totality.
- L = 1: Dark eclipse, gray or brownish coloration, details distinguishable only with difficulty.
- L = 2: Deep red or rust-colored eclipse, with a very dark central part in the shadow, and outer edge of the umbra relatively bright.
- L = 3: Brick red eclipse, usually with a bright or yellow rim to the shadow.
- L = 4: Very bright copper-red or orange eclipse, with a bluish, very bright shadow rim.
If you observe the moon's luminosity during the eclipse and want to share what you saw, please send your Danjon estimate to Space.com Skywatching Columnist Joe Rao at firstname.lastname@example.org. Examine the moon at the beginning, middle and end of totality to get an impression of both the inner and outer umbra. In noting an L observation, state the time and optical means (naked eye, binoculars or telescope) used during the eclipse.
At mid-totality, from rural locations far from city lights, the darkness of the sky is impressive. Keen observers may be able to see faint stars and the clouds of the Milky Way. During totality, the moon will be positioned just a couple of degrees away from the star Spica in the constellation Virgo. Although Spica is one of the 21 brightest stars in the sky, the moon will almost seem to overwhelm the star with its light before the eclipse begins. But during totality, Spica will become much more conspicuous and its bluish color will contrast strikingly with the eerie, ruddy moon.
High above and to the right of the darkened moon, a brilliant yellow-orange "star" will shine with a steady glow. That will be the planet Mars, which will make its closest approach to Earth in 2014 just hours before the start of the eclipse.
From across the eastern third of Australia, Papua, New Guinea and the eastern half of Russia's Kamchatka Peninsula, the, moon will rise during totality on the evening of April 15. Because of low altitude and bright evening twilight, observers in these locations may not see much of the moon until it begins to emerge from out of Earth’s shadow.
Conversely, along the west coast of Iceland (including the capital, Reykjavik) as well as southern Greenland, the moon will set during totality on the morning of April 15. Because of low altitude and bright morning twilight, any observers in these locations may not see much of the moon at all after it slips completely into Earth’s shadow.
As totality ends, the eastern edge of the moon begins to emerge from the umbra, and the sequence of events repeats in reverse order until the spectacle is over.
Editor's Note: If you snap an amazing picture of the April 15 total lunar eclipse, you can send photos, comments and your name and location to managing editor Tariq Malik at email@example.com.
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for News 12 Westchester, N.Y. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.