Sky Roundup: February 26, 2007

If we could observe the entire lunar eclipse set for March 3rd, this is how it might appear!  The Full Moon enters the Earth’s shadow, turns reddish, then brightens as it re-emerges from that shadow.  If it’s clear weather, we’ll see the eclipse already in progress and may witness the right half of the eclipse time lapse pictured here. (Image by Forrest Egan )

Light and Shadow

From late February through early March, we endure the highs and lows of temperature as a warm seasonal regime tries to displace this cold season we’ve had in recent weeks. The weather seems tentative, uncertain for full warmth but not fully free from cold.  The light of day lengthens, the length of shadows shorten. Too, the night sky shows us some tension, but with less drama: Winter constellations are being gradually replaced by the star patterns for the season of Spring. 

Orion the Hunter and Taurus the Bull are pressing their eternal sky battle toward the western horizon as Leo the Lion and Boötes the Herdsman are on the move above the eastern horizon. The change in constellations is played out between the change of seasons with lights and shadows. The lights in late February come from the bright stars, Aldebaran in Taurus and both Betelguese and Rigel in Orion; the shadows in early March arrives with the silhouette of Earth against the Moon.

Throughout the passing Winter, brighter stars rule. In addition to the brilliant, colorful beacons in Orion (Betelguese, a deep orange-red; Rigel, a dazzling blue-white), the ruddy eye of Taurus the Bull (Aldebaran) and its companion star clusters (the Hyades and the Pleiades), offer night-sky delights. The change of seasons gives some new material to view, too. Leo has a host of distant galaxies to view with telescopes; its bright heart, the star Regulus, is easy to spot with the unaided eye. The constellation’s fainter pattern nearby, Cancer the Crab, hosts a neat little cluster of stars, known as the Beehive.

Shadows, too, cross the night sky in this transition from Winter to Spring. On March 3rd, Earth passes between Sun and Moon, so exactly that the shadows of Earth play across the face of the Moon in a lunar eclipse. From our vantage in Cleveland, the eclipse itself will already be underway at sunset as the Full Moon rises in the north-northeast. If weathers permits, and it’s clear outside, we’ll see the rise of a fully lighted Moon moving in the shadows of Earth.

At first, the Moon’s sunlit face passing into Earth’s shadow is barely affected since the leading edge of the Earth’s shadow, known as the penumbra, does not reduce appreciably the light of the Full Moon. As it advances in its orbit, the Moon plunges deeper into the full shadow of the Earth, the umbra, which then does notably diminish its light.

To the casual observer, at full eclipse a curious look comes over the Moon’s face.  It turns reddish, or perhaps a color ranging from bright orange to deep crimson to cherry-black. This effect is indeed real; the shadow of Earth creates a different light on the Moon. The light comes from sunlight filtering through the Earth’s atmosphere and falling on the Moon’s surface; most of that light, except for longer wavelengths, are filtered out, hence the reddish color one sees on the face of the Moon. 

As the eclipse concludes, the Moon glides out of the darker silhouette of Earth’s umbra, the reddish effect gradually disappears; the Moon brightens appreciably and continues its way through the penumbra. From first contact of Earth shadow’s leading edge to last contact with the trailing edge of the penumbra spans over six hours. However, since we in Cleveland will witness the Moon already eclipsed by the Earth’s umbra, our view of this phenomenon will last about three hours as we watch the Full Moon return bright and shining. By the way, this eclipse is completely safe to watch, fairly easy to photograph, and, weather permitting, can conceivably be witnessed by half the world.

As the weather may seem uncertain this time of year, the play of light and shadow can make this change of season surely memorable.

Observing note:   The Astronomy staff at the Cleveland Museum of Natural History hopes to make the March eclipse event memorable and will help to deploy telescopes on Wade Oval, weather permitting, to view the lunar eclipse this Saturday, March 3rd. 

If it’s clear, let’s hope we get a glimpse. Unfortunately, the Mueller Observatory will not be open for this particular astronomical event since we cannot position the telescope well enough to see the eclipse as it rises into view.