A Beginners Guide To Eclipses

 

Ever since people first started looking up at the sky and tried to understand what they saw, eclipses have fascinated, awed, and terrified humans. Although the cause of eclipses are well understood today, for good reason they remain the most awesome and incredible events in nature. This handy guide will give readers the basics of what an eclipse is and why they happen, what to expect during an eclipse and how to view and record the event, along with ways to involve children safely, and a handy checklist to use to plan your own eclipse event.

One easy question to answer is, "Are eclipses worth the effort to see?"

Our favorite reply to this question is that while all eclipses are interesting, the difference between seeing a partial eclipse versus a total solar eclipse is like the difference between meeting someone nice, and marrying them. Put another way, if you have an opportunity and the means to see a total eclipse, you absolutely should make every effort to do so.

The Types of Eclipses

An eclipse occurs when one astronomical body passes into the shadow of another. On earth, there are two general types of eclipses that happen, lunar eclipses and solar eclipses. 

These two types are shown below, with a lunar eclipse at the top and a solar eclipse below.

In both cases there are two parts to the shadow that's cast by the eclipsing body: the umbra or inner shadow, and the penumbra or outer shadow. In the case of the lunar eclipse shown at the top, as the moon passes through the Earth's shadow the eclipse will be visible to almost everyone located on the night side of the Earth.

In the case of solar eclipses the moon passes between the sun and the Earth. Anyone in the penumbra will see a partial eclipse, while people located in the narrow path that the umbra traces out on the Earth's surface will see either a total solar eclipse, or an annular eclipse (for more on why there are different types of eclipses and how they differ, check out this page for more detailed information).

Eclipses occur and look the way they do from Earth because of a happy coincidence in the relative sizes of the sun and moon in the sky. Even though the sun is much farther away from the Earth than the moon, both appear to be about 1/2 of a degree in diameter.

How To View A Lunar Eclipse

Of the two major types of eclipses, lunar eclipses are by far the simplest to observe, requiring only clear skies and no other special equipment. All that's really required to view a lunar eclipse is to go outside and look up during one, weather permitting. If you're interested in photographing either lunar or solar eclipses, head over to our handy guide for more information.

Viewing Solar Eclipses

Solar eclipses are more complicated to observe and due to the sun's inherent brightness great caution must be used when observing them, though high cost need not necessarily be a factor.

WARNING: During the partial stages of any solar eclipse it's very important to use eye protection while observing because with even just 1% of the sun's disc not covered by the moon eye damage or blindness can result. Viewers should use only protection specifically made for viewing the sun's disc.

Many people decide to get solar eclipse glasses for each person in your group to view the eclipse and these allow a viewer to look directly at the sun, which usually appears orange. Normally the disc of the sun appears round using the glasses, but during a solar eclipse the moon will appear to "take a bite" out of the sun.

Another easy, low tech way to view a solar eclipse is to use a pinhole projector. The simplest way to do this is to take an ordinary kitchen colander like this one outside during the partial phases of a solar eclipse. The shadow that is cast will consist of many dots of sunlight. As the eclipse progresses, these small dots will take on a distinctly crescent shape. Even leaves from a tree can cast a shadow with many crescents on the ground.

You can also make a slightly more sophisticated pinhole viewer using the instructions here.

Besides using a pinhole projector, you can also use either a small telescope to project the disc of the sun onto a piece of white cardboard. First, if your telescope is larger than about 3 inches in diameter, you should consider using a circular mask to block some of the light from entering the telescope.

To make a mask, simply cut out a piece of cardboard large enough to cover the entire front end of the telescope, and make a round 1 inch hole in it and securely tape it to the front of the scope. The purpose of using a mask is to minimize the amount of sunlight entering the telescope that is brought to focus near the eyepiece. Even a modest 2.5 inch telescope can focus a tremendous amount of heat that can crack an eyepiece or start a fire.

After the mask is attached, just point the scope toward the sun. DO NOT LOOK DIRECTLY THROUGH THE TELESCOPE!

As you're pointing the telescope at the sun, hold a piece of white paper a few inches behind the eyepiece (to point the scope at the sun as you do this, just look at the shadow the scope casts on the paper, and try to make it as small and round as possible. At this point you should see a fuzzy white circle on the paper.

To focus the sun's image, just turn the telescope focus knob until the edge of the sun is sharp and well defined. You can control how large the image is on the paper by varying the distance from the eyepiece to the paper.

Be sure not to allow anyone to look through the scope, and keep a careful watch on children.

You can also use a small telescope with a solar filter. Many telescopes come with a "solar filter" that can be screwed into the end of a telescope eyepiece. If you have one of these throw it out immediately - using these can be quite dangerous because if you're looking through one, all of the heat and light is focused onto the glass filter, which can crack and break suddenly and without warning. If this happens anyone looking through the scope can be blinded instantly.

Instead, make a mask as described above to reduce the amount of light coming into the telescope, and then use a piece of solar film made for viewing the sun directly and tape it securely over the entire hole in the mask. Make sure the hole is completely covered for safety.

If you then point the scope at the sun as described above and look into the eyepiece you should see all or part of the sun's disc, and the moon passing in front of it.

If you're lucky enough to see a total solar eclipse, during totality it is safe to view the eclipse directly with your eyes, but you MUST put safety equipment back on before totality ends and any part of the solar disc is uncovered.

Sharing Eclipses With Children

Involving children in observing eclipses can be fun and educational, and can lead to a lifelong interest in science and nature. Eclipses afford an opportunity to talk about the distances from the Earth to the moon or sun, and the phases of the moon.

During a total solar eclipse there are many interesting things to point out too. The most obvious thing that occurs during totality is darkness at a time when it's not normally dark. As totality approaches observers looking west may see a "wall of darkness" rushing toward them at very great speed.

As totality actually begins, the air temperature often drops several degrees, and birds may stop singing. Brighter stars and planets will become visible in the darkened sky and online astronomy resources like Sky and Telescope magazine offer charts and guides describing how to find them.

Perhaps most disconcerting is that during totality, the sky appears something like it does during after sunset at twilight, except that the the twilight light comes from 360 degrees around you rather than only in the west. After a few moments, the observer may notice a wall of light rapidly approaching from the west, and as the first slim edge of the solar disc is uncovered daylight returns.

The important thing to be aware of with children observers is to make sure they are safe. Even with repeated warnings kids might forget to put the eclipse glasses back on as totality ends, so make sure to say out loud when it's time, and take a look to make sure they have done so.

Eclipse Resources

Sky & Telescope Magazine - Founded in 1941, Sky & Telescope is one of the best respected resources for astronomy related information for amateur astronomers.

Space Weather - Features useful information about solar related phenomenon including current sunspot numbers, aurora predictions, etc.

Time & Date 2024 Eclipse Page - A guide to the path, times, and circumstances for the total eclipse taking place on April 8, 2024.