What is Solar Eclipse ?

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Positions of the sun, moon and Earth during a solar eclipse. Umbra and penumbra are regions of the moon's shadow.

A solar eclipse occurs when the moon passes in a direct line between the Earth and the sun. The moon's shadow travels over the Earth's surface and blocks out the sun's light as seen from Earth.

an eclipse to take place, the moon must be in the correct phase during an eclipse season; for a solar eclipse, it must be a new moon. This condition makes solar eclipses relatively rare.

A solar eclipse is a spectacular sight and a rare astronomical event. Each one is only visible from a limited area.

Solar eclipses can have a maximum point which is either partial, annular, or total. Hybrid eclipses have an annular and total maximum point in different locations.

An eclipse of the Sun happens when the New Moon moves between the Sun and Earth, blocking out the Sun's rays and casting a shadow on parts of Earth.

Partial solar eclipses occur when the Moon only partly obscures the Sun's disk and casts only its penumbra on Earth.

Solar eclipses are only visible from within the area on Earth where the Moon's shadow falls, and the closer you are to the center of the shadow's path, the bigger the eclipse looks.

Solar eclipses are usually named for their darkest, or maximum, point. The exception is the hybrid eclipse.

Solar eclipses are usually named for their darkest, or maximum, point. The exception is the hybrid eclipse.

The darkest point of solar eclipses is only visible from a small area. In most places and for most of the duration, total, annular, and hybrid eclipses look like a partial solar eclipse.

a solar eclipse to take place, the Sun, the Moon, and Earth must be aligned in a perfect or near perfect straight line–an alignment astronomers call syzygy.

The New Moon has to be near a lunar node. These nodes are 2 points where the plane of the Moon's orbital path around Earth meets Earth's orbital plane around the Sun–the ecliptic.

The paths meet because the plane of the Moon's path around Earth is inclined at an angle of approximately 5° to the ecliptic.

This will be the first total solar eclipse in the continental U.S. in 38 years. The last one occurred February 26, 1979. Unfortunately, not many people saw it because it clipped just five states in the Northwest and the weather for the most part was bleak. Before that one, you have to go back to March 7, 1970.

A solar eclipse is a lineup of the Sun, the Moon, and Earth. The Moon, directly between the Sun and Earth, casts a shadow on our planet. If you’re in the dark part of that shadow (the umbra), you’ll see a total eclipse. If you’re in the light part (the penumbra), you’ll see a partial eclipse.

A solar eclipse happens at New Moon. The Moon has to be between the Sun and Earth for a solar eclipse to occur. The only lunar phase when that happens is New Moon.

Solar eclipses don’t happen at every New Moon. The reason is that the Moon’s orbit tilts 5° to Earth’s orbit around the Sun. Astronomers call the two intersections of these paths nodes. Eclipses only occur when the Sun lies at one node and the Moon is at its New (for solar eclipses) or Full (for lunar eclipses) phase. During most (lunar) months, the Sun lies either above or below one of the nodes, and no eclipse happens.

Eclipse totalities are different lengths. The reason the total phases of solar eclipses vary in time is because Earth is not always at the same distance from the Sun and the Moon is not always the same distance from Earth. The Earth-Sun distance varies by 3 percent and the Moon-Earth distance by 12 percent. The result is that the Moon’s apparent diameter can range from 7 percent larger to 10 percent smaller than the Sun.

It's all about magnitude and obscuration. Astronomers categorize each solar eclipse in terms of its magnitude and obscuration, and I don’t want you to be confused when you encounter these terms. The magnitude of a solar eclipse is the percent of the Sun’s diameter that the Moon covers during maximum eclipse. The obscuration is the percent of the Sun’s total surface area covered at maximum. Here's an example: If the Moon covers half the Sun's diameter (in this case the magnitude equals 50 percent), the amount of obscuration (the area of the Sun's disk the Moon blots out) will be 39.1 percent.

Solar eclipses occur between Saros cycles. Similar solar and lunar eclipses recur every 6,585.3 days (18 years, 11 days, 8 hours). Scientists call this length of time a Saros cycle. Two eclipses separated by one Saros cycle are similar. They occur at the same node, the Moon’s distance from Earth is nearly the same, and they happen at the same time of year.

Everyone in the continental U.S. will see at least a partial eclipse. In fact, if you have clear skies on eclipse day, the Moon will cover at least 48 percent of the Sun’s surface. And that’s from the northern tip of Maine.

. It’s all about totality. Not to cast a shadow on things, but likening a partial eclipse to a total eclipse is like comparing almost dying to dying. I know that 48 percent sounds like a lot. It isn’t. You won’t even notice your surroundings getting dark. And it doesn’t matter whether the partial eclipse above your location is 48, 58, or 98 percent. Only totality reveals the true celestial spectacle: the diamond ring, the Sun’s glorious corona, strange colors in our sky, and seeing stars in the daytime.

1. You want to be on the center line. This probably isn’t a revelation, but the Moon’s shadow is round. If it were square, it wouldn’t matter where you viewed totality. People across its width would experience the same duration of darkness. The shadow is round, however, so the longest eclipse occurs at its center line because that’s where you’ll experience the Moon’s shadow’s full width.