8 rare phenomena to watch for during the total solar eclipse

If you can, find a clear view of the horizon for the event. In the few minutes before and after totality the moon will move across the sun triggering what will look like a unique 360-degree sunset.

Sunset, and sunrise, colors occur when sunlight passes through more of the atmosphere low in the sky and hits dust and moisture in the air. The light is scattered as a result, which makes it appear yellow, orange, and red.

During totality, light from outside the moon's shadow takes a similar path, and your eyes perceive it the same way, so the entire horizon will look like one giant sunset.

As the moon moves across the sun, it blocks more and more light, until only the thinnest outer edge of the sun's photosphere (a layer of the sun) is visible in the moments just before and after totality. This outer edge, called the limb, is cooler than the center of the sun and therefore looks different to our eyes.

So, when only the limb is visible just before and after totality, "the whole color of the sky changes," taking on a purple or silvery hue, Fienberg said.

Right now, the sun is approaching its highest level of magnetic activity, a time known as solar maximum that occurs about every 11 years. This means more sunspots, which are giant dark circles on the solar surface that can be many times the size of Earth.

Using binoculars or a telescope with a sun-safe filter, sunspots will be very obvious during the periods of partial eclipse, Fienberg said.

"You can watch as the moon gobbles them up and spits them back out." You can even track when and where sunspots will be on the day of the eclipse by visiting SpaceWeatherLive.com.

You can also turn your gaze to the sun's edge to potentially spot solar flares — giant prominences that shoot off the solar surface. They will look neon pink.

Back before eclipse glasses and solar filters, the only safe way to observe an eclipse before and after totality was through pinhole projection.

Here's how it works: when sunlight passes through a small area — like a pinhole, leaves on a tree, or holes in a colander — the shadow reflects the sun's crescent shape.

If you stand with your back to the sun, holding an item that has small holes (Fienberg suggests a Ritz cracker or a slotted serving spoon with holes), you'll see tiny crescent shapes amid the shadows on the ground.

"People have a lot of fun with that," Fienberg said.

In the moments before, during, and after the total eclipse, "two planets will become very obvious," Fienberg said. Jupiter will be to the upper left of the sun, and Venus (the brighter of the two) to the lower right.

Venus should appear first, about ten minutes before totality while Jupiter will become most obvious during totality, but might also be visible a few minutes right before and after.

As the moon passes over the sun, it obscures the light. But "the moon is not a smooth sphere like marble," Fienberg said. "It's rough," due to mountains, valleys, and craters. That leads to one of the most remarkable eclipse phenomena: Baily's beads, named for English astronomer Francis Baily, who explained them in 1836.

"Baily's beads are the last bits of sunlight visible through deep valleys on the surface of the moon, before it entirely covers the sun," Fienberg said. They appear like round blazes of sunlight about 10 seconds before and after totality.

Baily's beads explain another eclipse phenomenon: the diamond ring effect. This happens when the moon has almost entirely covered the sun, and there's only one more bead of sunlight uncovered.

At this point, the corona, or outermost layer of the sun, begins to be visible. The result is a stunning ring of sunlight with one large prominence, which looks just like a diamond solitaire in the sky.

Spotting the diamond ring effect can be difficult because it only lasts an instant and you won't see it if you still have your eclipse glasses on. But it's also important to keep your glasses on up to the moment totality begins, when the moon fully obscures the sun and it's safe to remove your glasses.

Because of that, Fienberg recommends looking for the diamond ring effect just after totality. Leave your glasses off, then reapply them right after the diamond ring appears.

Once the moon entirely covers the sun's surface, you'll be able to see the corona, or outermost part of the sun's atmosphere. It will appear like a bright, symmetrical glow coming from behind the moon's shadow.

Normally, our eyes can't perceive the corona because the surface of the sun appears too bright, so totality is a unique opportunity for this.

Plus, it'll be especially spectacular this year because the corona's appearance changes with the level of solar magnetic activity. Since the sun is approaching solar maximum, the corona will appear more vibrant, symmetrical, and larger in April than it has during past eclipses.

"It's really dramatic," Fienberg said.