Lunar eclipse tonight

The first total eclipse of the moon visible in more than three years in the eastern third of the United States will occur tonight.

For more than three hours the effect of the Earth’s shadow will be clearly seen (weather-permitting). The best time to view the eclipse in the Northwest will be from 8:30 p.m. on.

Even if it’s too cloudy to see the show, Americans will have another chance on Nov. 8, with viewing best again in the East.

Eclipses of the moon aren’t the only celestial events on the calendar. This year marks Earth’s closest approach to the planet Mars in recorded history. Also, at the end of this month, there will be a kind of solar eclipse, but it won’t be visible from the continental United States.

The exact color of a lunar eclipse is hard to predict but most take on sunset colors; rust, red, orange, salmon or pink. In fact, the colors arise from the same effect that brings us the varying hues of the setting sun: the distortion of light by the Earth’s atmosphere.

When the moon goes into eclipse, the Earth blocks any direct sunlight. The moon doesn’t disappear completely, however, because some sunlight passing by the Earth is bent by our atmosphere, allowing it to reach the moon and be reflected back to us.

A phenomenon called atmospheric scattering alters the moon’s apparent color. Molecules in our atmosphere absorb and re-emit light, and scatter, or disperse blue light all around the sky while letting the redder part of the spectrum pass through.

The exact color will depend on what’s going on in the parts of the atmosphere that the light passes through. Clouds can affect the color, as can volcanic ash. For a few years after the 1991 eruption of Mount Pinatubo in the Philippines, the moon in eclipse looked almost black.

“Some lunar eclipses are more brownish, some are orange, and some are more reddish,” said Robert Naeye, an amateur astronomer and editor of Mercury Magazine, put out by the Astronomical Society of the Pacific. “It really does vary from eclipse to eclipse. “That’s what makes it fun.”

If you were on the moon during a lunar eclipse, you’d see a spectacular eclipse of the sun, with some reddened sunlight creating a halo around our planet.

Lunar eclipses generally occur several times a year somewhere on the planet, and about half of those are visible from any given place. If the orbit of the moon were in the same plane as the orbit of the Earth around the sun, we’d have a lunar eclipse every month. Instead, the moon’s orbit is tilted with respect to ours around the sun, so most months there is no eclipse.

Solar eclipses, on the other hand, happen when the moon comes directly between the Earth and the sun. That occurs less often than a lunar eclipse because the diameter of the moon is about a quarter that of Earth. It has to pass through a very narrow space to actually block out the disk of the sun.

Sometimes the moon is too far away to cause a total eclipse. If it’s at a very distant part of its elliptical orbit, it won’t completely cover the disk of the sun. Instead, it blocks only in the middle of the sun, letting a ring of sunlight shine around it. Such an annular eclipse will take place May 31, though it will be visible only from parts of northern Scotland, Iceland and Greenland. Other areas, mostly across Europe and Asia, will get a partial eclipse, in which the moon takes a bite out of the sun.

Then, on Aug. 28, Mars will make its closest approach to Earth – less than 35 million miles _ in tens of thousands of years. The Red Planet will get brighter through the summer and stay unusually bright into the early autumn.

Astronomers disagree over just how long it’s been since Mars passed this close.

“Some are saying 50,000 years, some 60,000 years, others as many as 73,000 years,” said Naeye.

They refer to this close approach as opposition. It happens, to some degree, almost every year when the Earth passes Mars. (Think of a runner on the inside lane of a track passing another in a lane farther out.) Because Mars’ orbit is more elliptical than Earth’s, the two planets don’t always approach at the same distance. This time it will be unusually close.