Shadows in the sky
The path of the moon through Earth's umbral and penumbral shadows during the total lunar eclipse of Feb. 20, 2008. (Times are in ET.) (Fred Espenak, NASA/Goddard Space Flight Center)
In Depth
Space
Shadows in the sky
What to expect during lunar and solar eclipses
Feb. 19, 2008
By Paul Jay, CBC News
The totality of the solar eclipse is seen at Ceduna in South Australia on Dec. 4, 2002. (Russell McPhedran/Associated Press)
On the night of Wednesday, Feb. 20, at 10:01 p.m. ET, Canadian skywatchers with a favourable weather forecast will be able to witness the moon fall under Earth's shadow, its colour shifting to a darker, reddish hue.
The total lunar eclipse, which will last about 50 minutes, is the third to occur in the past year, but the first that will be seen across Canada: the two previous total lunar eclipses, both in 2007, were only visible in parts of the country.
In general, an eclipse occurs whenever an astronomical body, such as a planet or moon, comes between a source of light, such as a star, and another body, casting a shadow.
Quick Fact
When astronomers in ancient Greece observed that the shadow of the Earth on the moon during a lunar eclipse was always circular, they realized the Earth was a sphere.
On Earth, though, when we talk about eclipses, we're usually talking about one of two types: lunar or solar.
Lunar eclipse
A lunar eclipse occurs when the Earth comes between the sun and the moon, casting the Earth's shadow on the moon. Such an eclipse is generally only noticeable when the moon travels into the dark inner potion of the Earth's shadow, the umbra.
If the moon goes completely into the umbra, it's called a total lunar eclipse. If only part of the moon becomes dark, it's called a partial lunar eclipse.
Even during a total eclipse, the moon doesn't become completely dark. Light from the sun filters and bends through the Earth's atmosphere and can shine on the moon. The amount of light that reaches the moon depends on the amount of clouds and dust in the atmosphere. And because clouds and dust refract blue light from the sun, the moon glows a coppery-red during a lunar eclipse.
Lunar eclipses only occur during a full moon, but because the moon's orbit around the Earth is tilted relative to the Earth's orbit around the sun, we don't see an eclipse at every full moon.
The moon during a lunar eclipse in 2003. Sunlight that leaks through the Earth's atmosphere can give the moon a copper or brown colour. (Michael Sohn/Associated Press)
Those who miss Wednesday's event will have to wait a few years before their next opportunity comes: North Americans won't see another total lunar eclipse until Dec. 21, 2010.
Solar eclipse
When the moon moves in front of the sun from our perspective on Earth, a solar eclipse occurs. These are typically more dramatic than lunar eclipses since the daytime sky can go eerily dark for several minutes as the moon blots out the sun's light.
If the moon completely covers the sun, it's called a total solar eclipse, a rare event. However, if a ring of the sun is still visible around the silhouette of the moon, it's called an annular eclipse. This change in the apparent size of the moon relative to the sun occurs because the moon's orbit isn't perfectly circular, so the moon can be closer to the Earth at certain times.
In some cases, an eclipse can be total when observed from some locations and annular from others, because of the curvature of the Earth. In either case, astronomers can use the opportunity to study the sun's corona, the outer layer of the sun's atmosphere, and solar flares.
If only part of the sun is blotted out by the moon, it's called a partial solar eclipse.
It is never safe to look directly at the sun, even during an eclipse, as the light and radiation can harm one's eyesight. Eclipses are usually viewed by projecting an image of the sun onto a piece of paper though either a lens, such as a telescope, or a pinhole in a piece of cardboard.
The next total solar eclipse that will be visible across North America will be on Aug. 21, 2017.
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