Look heavenwards on the evening of January 20th to enjoy one of nature’s celestial wonders: the total eclipse of the moon.
Fred Espenak of NASA has prepared a press release on his website, which announces that “a total eclipse of the Moon will be visible from all of North and South America including the USA and Canada. The event will also be visible from western Europe on the morning of January 21.”
What is a total eclipse of the moon? It is when the Moon is plunged into total darkness by the shadow of the Earth. It occurs when Earth passes on its orbit between the Sun and the Moon such that Earth’s shadow completely prevents sunlight from illuminating the Moon.
Explains Espenak, “An eclipse of the Moon can only take place at full moon, and only if the Moon passes through some portion of the Earth’s shadow. The shadow is actually composed of two cone-shaped components, one inside the other. The outer or penumbral shadow is a zone where some portion of the Sun’s rays are blocked. In contrast, the inner or umbral shadow is a region devoid of all direct sunlight.”
Espenak tells us that total lunar eclipse events “are quite striking for the vibrant range of colors the Moon can take on during totality.” That is the term describing the total eclipse, when the moon is completely in Earth’s shadow.
But why are there colors?
Espenak explains that the Earth blocks all direct sunlight from the Moon, but that some light does filter through.
“While the Moon remains completely within Earth’s umbral shadow, indirect sunlight still manages to reach and illuminate it. However, this sunlight must first pass deep through the Earth’s atmosphere, which filters out most of the blue colored light. The remaining light is a deep red or orange in color and is much dimmer than pure white sunlight. The Earth’s atmosphere also bends or refracts some of this light so that a small fraction of it can reach and illuminate the Moon.”
The scientist and author continues, noting that “the total phase of a lunar eclipse is so interesting and beautiful precisely because of the filtering and refracting effect of Earth’s atmosphere. If the Earth had no atmosphere, then the Moon would be completely black during a total eclipse. Instead, the Moon can take on a range of colors from dark brown and red to bright orange and yellow. The exact appearance depends on how much dust and clouds are present in Earth’s atmosphere. Total eclipses tend to be very dark after major volcanic eruptions since these events dump large amounts of volcanic ash into Earth’s atmosphere. During the total lunar eclipse of December 1992, dust from Mount Pinatubo rendered the Moon nearly invisible.”
Total eclipses actually pass through three phases. When the Earth is just starting to block sunlight from reaching the Moon, a penumbral eclipse (too difficult for us to see with our naked eyes) occurs. Then, as the Earth’s shadow grows over the face of the Moon, the penumbral eclipse turns into a partial eclipse.
Then the total eclipse occurs, when the Moon is totally covered by Earth’s shadow. This phase is followed by the partial and last, penumbral eclipse.
This Thursday’s total lunar eclipse will take three and a half hours from start to finish.
Says Espenak; “The partial eclipse begins as the Moon’s eastern edge slowly moves into the Earth’s umbral shadow. During the partial phases, it takes just over an hour for the Moon’s orbital motion to carry it entirely within the Earth’s dark umbra. Since no major volcanic eruptions have taken place recently, the Moon will probably take on a vivid red or orange color during the 77 minute long total phase. After the total phase ends, it is once again followed by a partial eclipse as the Moon gradually leaves the umbral shadow.”
Of course, depending on where you live, and what time zone you are in, the eclipse will occur at different times. Here in Eastern Standard Time, the partial eclipse will begin at 10:01; the total eclipse will begin at 11:05 p.m. with mid-eclipse at 11:44 p.m. The total eclipse ends at 12:22 a.m. on January 21, and the last partial eclipse ends at 01:25 a.m., January 21.
Eric and I are hoping for a clear night on Thursday. If there is, it ought to be a dandy night to head out and peer heavenwards.
Why not have an “eclipse party” and celebrate this beautiful phenomenon with friends.
Find Espenak’s home page at http://sunearth.gsfc.nasa.gov/eclipse/SEextra/TLE2000Jan20.html.
Are your feeders clean & full of black sunflower seed, Niger seed and suet? We are enjoying large flocks of blue jays, evening grosbeaks, red polls, siskins, chickadees… and so far, a solitary pine grosbeak (the raspberry-purple members of this family). Do you have any interesting bird sightings to report?
Katharine Fletcher is a freelance writer living near Quyon, where she enjoys the night sky. Contact her at firstname.lastname@example.org