How a lunar eclipse works.
Why the moon sometimes glows red during a total lunar eclipse.
From North America, look southeast at mid-eclipse to see the Moon nestled between Regulus and Saturn.On Wednesday night, Feb. 20, for the third time in the past year, the moon will become completely immersed in the Earth's shadow, resulting in a total lunar eclipse.
As is the case with all lunar eclipses, the region of visibility will encompass more than half of our planet. Nearly a billion people in the Western Hemisphere, more than 1.5 billion in Europe and Africa, and perhaps another half-billion in western Asia will be able to watch — weather permitting — as the brilliant mid-winter full moon becomes a shadow of its former self and morphs into a glowing coppery ball.
Almost everyone in the Americas and Western Europe will have a beautiful view of this eclipse if bad weather doesn't spoil the show. The moon will be high in a dark evening sky as viewed from most of the United States and Canada while most people are still awake and about.
Local conditions
The only problematic area will be along the Oregon and northern California coast, where the first partial stage of the eclipse will already be under way when the moon rises and the sun sets on Wednesday evening. But if you have an open view low to the east, even this situation will only add to the drama, for as twilight fades, these far-Westerners will see the shadow-bitten moon coming into stark view low above the landscape. And by late twilight observers will have a fine view of the totally eclipsed lunar disk glowing red and dim low in the eastern sky.
Alaskans will also see the moon rise during the eclipse; in fact, much of western Alaska will see the moon rise while completely immersed in the Earth's shadow.
For Hawaiians, moonrise unfortunately comes just after the end of totality, with the moon gradually ascending the sky and its gradual emergence from the shadow readily visible.
Western Europe and Africa also will get a good view of the eclipse, but at a less convenient time: before dawn on Thursday morning, Feb. 21.
Total triangle
Moreover, this eclipse comes with a rare bonus. The planet Saturn (magnitude +0.2) and the bright bluish star, Regulus (magnitude +1.4) will form a broad triangle with the moon's ruddy disk.
Careful watchers will notice the moon changing its position with respect to the star and planet as it moves eastward through the Earth's shadow.
Saturn's position will also depend somewhat on your location. Seen from North America, the great ringed planet will be 3.5 degrees above and to the left of the moon's center at mid-totality (3:26 Universal time February 21st). At the same moment, Regulus will sit just 2.8 degrees above and to the right of the moon.
Some old-time astronomy buffs may remember from 40 years ago a total lunar eclipse with the moon sitting only about a degree from Spica — a gorgeous celestial tableau! More recently, in 1996, a totally eclipsed moon passed within 2 degrees of Saturn.
But this upcoming double event will be the only one of its kind occurring within the next millennium!
Colors and brightness
There is nothing complicated about how to view this celestial spectacle. Unlike an eclipse of the sun, which necessitates special viewing precautions in order to avoid eye damage, an eclipse of the moon is perfectly safe to watch. All you'll need to watch are your eyes, but binoculars or a telescope will give a much nicer view.
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, Andre 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.
Examine the moon at mid-totality and also near the beginning and end of totality to get an impression of both the inner and outer umbra.
At mid-totality, the darkness of the sky is very impressive. Faint stars, which were completely washed-out by the brilliant moonlight prior to the eclipse, become visible and the surrounding landscape takes on a somber hue. 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.
Unless airborne volcanic aerosols or other unusual atmospheric effects influence its appearance, the moon's disk should appear moderately bright, especially right around the beginning and end of totality. The lower part of the moon will likely appear brightest and glowing a ruddy or coppery hue, while the upper half of the moon should look more gray or chocolate in color.
Eclipse schedule
The eclipse will begin when the moon enters the faint outer portion, or penumbra of the Earth's shadow. The penumbra, however, is all but invisible to the eye until the moon becomes deeply immersed in it. Sharp-eyed viewers may get their first glimpse of the penumbra as a delicate shading on the left part of the moon's disk about 20 minutes before the start of the partial eclipse (when the round edge of the central shadow or umbra, first touches the moon's left edge). During the partial eclipse, the penumbra should be readily visible as a dusky border to the dark umbral shadow.
The moon will enter Earth's much darker umbral shadow at 1:43 on Feb. 21 by Greenwich or Universal time, which is 8:43 p.m. on Feb. 20 in the Eastern time zone, 7:43 p.m. Central time, 6:43 p.m. Mountain time and 5:43 p.m. Pacific time.
Seventy-eight minutes later the moon is entirely within the shadow, and sails on within it for 51 minutes (about average for a total lunar eclipse), until it begins to find its way out at the lower left (southeastern) edge.
The moon be completely free of the umbra by 9:09 p.m. Pacific time or 12:09 a.m. (Feb. 21) Eastern time.
The vaguer shading of the inner penumbra can continue to be readily detected for perhaps another 20 minutes or so after the end of umbral eclipse. Thus, the whole experience ends toward 12:30 a.m. for the East (with the re-brightened moon now sloping down along the high arc it describes across the sky), or during the mid-evening hours for the West.
For Europe and Africa, the mid-point of this eclipse occurs roughly between midnight and dawn on the morning of Feb. 21, and as such the moon will still be well placed in the western sky. At the moment of mid-totality (3:26 UT), the moon will stand directly overhead from a point in the Atlantic Ocean roughly several hundred miles to the northeast of the coast of Suriname.
There will be a partial eclipse of the moon that will be visible across much of Europe and Asia on the night of Aug. 16-17. About 81 percent of the moon's diameter will become immersed in the umbra, leaving only the upper part of the moon visible.
In 2009, there will be four lunar eclipses, one a slight partial and the three others which will be of the penumbral variety meaning that at best only a vague hint of a light shading or smudginess on the moon's disk might be detected — if anything at all.
But not until Dec. 21, 2010 will there be another total lunar eclipse; that one too will again favor the Americas.
So although we've had a veritable plethora of total eclipses of late, keep in mind that after next Wednesday, you'll have to wait almost three years until your next chance to see another.
As is the case with all lunar eclipses, the region of visibility will encompass more than half of our planet. Nearly a billion people in the Western Hemisphere, more than 1.5 billion in Europe and Africa, and perhaps another half-billion in western Asia will be able to watch — weather permitting — as the brilliant mid-winter full moon becomes a shadow of its former self and morphs into a glowing coppery ball.
Almost everyone in the Americas and Western Europe will have a beautiful view of this eclipse if bad weather doesn't spoil the show. The moon will be high in a dark evening sky as viewed from most of the United States and Canada while most people are still awake and about.
Local conditions
The only problematic area will be along the Oregon and northern California coast, where the first partial stage of the eclipse will already be under way when the moon rises and the sun sets on Wednesday evening. But if you have an open view low to the east, even this situation will only add to the drama, for as twilight fades, these far-Westerners will see the shadow-bitten moon coming into stark view low above the landscape. And by late twilight observers will have a fine view of the totally eclipsed lunar disk glowing red and dim low in the eastern sky.
Alaskans will also see the moon rise during the eclipse; in fact, much of western Alaska will see the moon rise while completely immersed in the Earth's shadow.
For Hawaiians, moonrise unfortunately comes just after the end of totality, with the moon gradually ascending the sky and its gradual emergence from the shadow readily visible.
Western Europe and Africa also will get a good view of the eclipse, but at a less convenient time: before dawn on Thursday morning, Feb. 21.
Total triangle
Moreover, this eclipse comes with a rare bonus. The planet Saturn (magnitude +0.2) and the bright bluish star, Regulus (magnitude +1.4) will form a broad triangle with the moon's ruddy disk.
Careful watchers will notice the moon changing its position with respect to the star and planet as it moves eastward through the Earth's shadow.
Saturn's position will also depend somewhat on your location. Seen from North America, the great ringed planet will be 3.5 degrees above and to the left of the moon's center at mid-totality (3:26 Universal time February 21st). At the same moment, Regulus will sit just 2.8 degrees above and to the right of the moon.
Some old-time astronomy buffs may remember from 40 years ago a total lunar eclipse with the moon sitting only about a degree from Spica — a gorgeous celestial tableau! More recently, in 1996, a totally eclipsed moon passed within 2 degrees of Saturn.
But this upcoming double event will be the only one of its kind occurring within the next millennium!
Colors and brightness
There is nothing complicated about how to view this celestial spectacle. Unlike an eclipse of the sun, which necessitates special viewing precautions in order to avoid eye damage, an eclipse of the moon is perfectly safe to watch. All you'll need to watch are your eyes, but binoculars or a telescope will give a much nicer view.
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, Andre 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.
Examine the moon at mid-totality and also near the beginning and end of totality to get an impression of both the inner and outer umbra.
At mid-totality, the darkness of the sky is very impressive. Faint stars, which were completely washed-out by the brilliant moonlight prior to the eclipse, become visible and the surrounding landscape takes on a somber hue. 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.
Unless airborne volcanic aerosols or other unusual atmospheric effects influence its appearance, the moon's disk should appear moderately bright, especially right around the beginning and end of totality. The lower part of the moon will likely appear brightest and glowing a ruddy or coppery hue, while the upper half of the moon should look more gray or chocolate in color.
Eclipse schedule
The eclipse will begin when the moon enters the faint outer portion, or penumbra of the Earth's shadow. The penumbra, however, is all but invisible to the eye until the moon becomes deeply immersed in it. Sharp-eyed viewers may get their first glimpse of the penumbra as a delicate shading on the left part of the moon's disk about 20 minutes before the start of the partial eclipse (when the round edge of the central shadow or umbra, first touches the moon's left edge). During the partial eclipse, the penumbra should be readily visible as a dusky border to the dark umbral shadow.
The moon will enter Earth's much darker umbral shadow at 1:43 on Feb. 21 by Greenwich or Universal time, which is 8:43 p.m. on Feb. 20 in the Eastern time zone, 7:43 p.m. Central time, 6:43 p.m. Mountain time and 5:43 p.m. Pacific time.
Seventy-eight minutes later the moon is entirely within the shadow, and sails on within it for 51 minutes (about average for a total lunar eclipse), until it begins to find its way out at the lower left (southeastern) edge.
The moon be completely free of the umbra by 9:09 p.m. Pacific time or 12:09 a.m. (Feb. 21) Eastern time.
The vaguer shading of the inner penumbra can continue to be readily detected for perhaps another 20 minutes or so after the end of umbral eclipse. Thus, the whole experience ends toward 12:30 a.m. for the East (with the re-brightened moon now sloping down along the high arc it describes across the sky), or during the mid-evening hours for the West.
For Europe and Africa, the mid-point of this eclipse occurs roughly between midnight and dawn on the morning of Feb. 21, and as such the moon will still be well placed in the western sky. At the moment of mid-totality (3:26 UT), the moon will stand directly overhead from a point in the Atlantic Ocean roughly several hundred miles to the northeast of the coast of Suriname.
There will be a partial eclipse of the moon that will be visible across much of Europe and Asia on the night of Aug. 16-17. About 81 percent of the moon's diameter will become immersed in the umbra, leaving only the upper part of the moon visible.
In 2009, there will be four lunar eclipses, one a slight partial and the three others which will be of the penumbral variety meaning that at best only a vague hint of a light shading or smudginess on the moon's disk might be detected — if anything at all.
But not until Dec. 21, 2010 will there be another total lunar eclipse; that one too will again favor the Americas.
So although we've had a veritable plethora of total eclipses of late, keep in mind that after next Wednesday, you'll have to wait almost three years until your next chance to see another.
By Joe Rao SPACE.com
Skywatching Columnist
Skywatching Columnist
