How do eclipses of the sun and moon occur

Today, we enjoy the sky show with a healthy appreciation of the majestic forces that keep our solar system running. A total eclipse of the Sun is a spectacular sight and should not be missed.

However, it is extremely dangerous to look directly at the Sun: even a brief exposure can damage your eyes. Normally, few rational people are tempted to do this because it is painful and something your mother told you never to do!

But during the partial phases of a solar eclipse, the temptation to take a look is strong. Think before you give in. Still, there are perfectly safe ways to follow the course of a solar eclipse, if you are lucky enough to be in the path of the shadow. The easiest technique is to make a pinhole projector. The hole produces a fuzzy but adequate image of the eclipsed Sun.

Watching hundreds of little crescent Suns dancing in the breeze can be captivating. A kitchen colander also makes an excellent pinhole projector. Although there are safe filters for looking at the Sun directly, people have suffered eye damage by looking through improper filters, or no filter at all. For example, neutral density photographic filters are not safe because they transmit infrared radiation that can cause severe damage to the retina.

Also unsafe are smoked glass, completely exposed color film, sunglasses, and many other homemade filters. Figure 5: Total Solar Eclipse. This map of the United States shows the path of the total solar eclipse of On August 21, , the shadow will first cross onto the West Coast near Portland, Oregon, traversing the United States and exiting the East Coast in South Carolina approximately 90 minutes later, covering about miles in the process. You should certainly look at the Sun directly when it is totally eclipsed, even through binoculars or telescopes.

Unfortunately, the total phase, as we discussed, is all too brief. And, despite the ancient folklore that presents eclipses as dangerous times to be outdoors, the partial phases of eclipses—as long as you are not looking directly at the Sun—are not any more dangerous than being out in sunlight. During past eclipses, unnecessary panic has been created by uninformed public officials acting with the best intentions.

There were two marvelous total eclipses in Australia in the twentieth century during which townspeople held newspapers over their heads for protection and schoolchildren cowered indoors with their heads under their desks. What a pity that all those people missed what would have been one of the most memorable experiences of their lifetimes. On August 21, , there will be a total solar eclipse visible across a large swath of the continental United States.

Annular solar eclipse The Moon is a bit farther from Earth than average, so a ring of sunlight encircles the Moon as it passes between Earth and Sun. This illustration shows the Moon passing through Earth's shadow during a typical lunar eclipse. The Moon is slightly tinted when it passes through the light outer portion of the shadow, the penumbra, but turns dark red as it passes through the central portion of the shadow, called the umbra.

When the Moon passes between Sun and Earth, the lunar shadow is seen as a solar eclipse on Earth. When Earth passes directly between Sun and Moon, its shadow creates a lunar eclipse. An occultation happens when an object blocks your view of another object.

In this case, the Moon blocks your view of the Sun. That means during the day, the Moon moves over the Sun and it gets dark. This total eclipse happens about every year and a half somewhere on Earth. A total solar eclipse was visible over the continental United States on Aug. This image was captured in Hopkinsville, Kentucky during the eclipse. But not everyone experiences every solar eclipse. Getting a chance to see a total solar eclipse is rare.

You have to be on the sunny side of the planet when it happens. Because the moon appears to pass directly in front of the sun, total, annular and hybrid eclipses are also called "central" eclipses to distinguish them from eclipses that are merely partial.

Eclipses do not happen at every new moon, of course. This is because the moon's orbit is tilted just over 5 degrees relative to Earth's orbit around the sun. For this reason, the moon's shadow usually passes either above or below Earth, so a solar eclipse doesn't occur. But as a rule, at least twice each year and sometimes as many as five times in a year , a new moon will align itself in just such a way to eclipse the sun.

That alignment point is called a node. Depending on how closely the new moon approaches a node will determine whether a particular eclipse is central or partial. And these alignments don't happen haphazardly, for after a specific interval of time, an eclipse will repeat itself or return. This interval is known as the Saros cycle and was known as far back as the days of the early Chaldean astronomers some 28 centuries ago. After this interval, the relative positions of the sun and moon relative to a node are nearly the same as before.

That third of a day in the interval causes the path of each eclipse of a series to be displaced in longitude a third of the way around Earth to the west with respect to its predecessor. For example, on March 29, , a total eclipse swept across parts of western and northern Africa and then across southern Asia. One Saros later, on April 8, , this eclipse will recur, except instead of Africa and Asia, it will track across northern Mexico, the central and eastern United States and the Maritime provinces of Canada.

As a solar eclipse approaches, the mainstream media often will provide a variety of warnings and advisories against looking at the sun with bare eyes, as blindness could ensue. This has given most people the idea that eclipses are dangerous. The sun constantly emits invisible infrared rays that can damage your eyes.

Ordinarily, we have no reason to gaze at the sun. An eclipse gives us a reason, but we shouldn't. By far, the safest way to view a solar eclipse is to construct a "pinhole camera.

Binoculars or a good telescope mounted on a tripod can also be used to project a magnified image of the sun onto a white card. The farther away the card, the larger you can focus the image. Look for sunspots. Notice that the sun appears somewhat darker around its limb or edge. This method of solar viewing is safe so long as you remember not to look through the binoculars or telescope when they are pointed toward the sun; put another way, never look directly at the sun when any part of its blindingly bright surface is visible.

A variation on the pinhole theme is the "pinhole mirror. Open a sun-facing window and place the covered mirror on the sunlit sill so it reflects a disk of light onto the far wall inside. The disk of light is an image of the sun's face.

The farther away from the wall is the better; the image will be only 1 inch across for every 9 feet or 3 centimeters for every 3 meters from the mirror. Modeling clay works well to hold the mirror in place. Experiment with different-sized holes in the paper. Again, a large hole makes the image bright, but fuzzy, and a small one makes it dim but sharp. Darken the room as much as possible. Be sure to try this out beforehand to make sure the mirror's optical quality is good enough to project a clean, round image.

Of course, don't let anyone look at the sun in the mirror.