Solar Eclipse What to See During an Eclipse

If you are lucky enough to find yourself inside the path of totality there's lots to see. Let's digress briefly and look at what there is to see on the sun itself.

Our thermonuclear furnace has a surface temperature of about 6000 degrees Celcius. The word "surface" is a bit misleading as the sun is not a solid ball, but rather a gaseous body. If you heat up a gas enough, it becomes ionized (the gas loses outer electrons) and the gas becomes opaque. This opaque and very bright surface of the sun is called the "photosphere." Because the gases of the photosphere are moderately dense, they give off an incandescent white light, like the filament of a lamp.

White-light solar image

 
The current white-light image of the sun from the Big Bear Solar Observatory (click for a larger version).
 
An image of the region around a sunspot. The mottled appearance is due to turbulent eruptions at the surface of the sun. (Photo courtesy National Solar Observatory, Sacramento Peak)
Before an eclipse starts—assuming you have the correct and safe viewing apparatus—you can view the entire face of the sun. This is a good chance to see sunspots. Sunspots are slightly cooler areas (about 1500 degrees C cooler) on the sun that look dark compared with the blinding photosphere. If you could move a sunspot off the surface of the sun and look at it all by itself, it would actually be very bright. It's just dark in comparison to the hotter surface near by.

 

Above the photosphere, the gases are cooler, more rarefied, and give off a spectrum of light that is representative of the chemical elements that compose that gas, mainly hydrogen. This thin layer, the upper atmosphere of the sun, is called the "chromosphere" because of its colorful nature. Normally you can't see the chromosphere, but the eclipse gives us just the right conditions to observe this beautiful phenomenon. There are always eruptions on the sun which throw huge amounts of glowing gas, often much larger than the earth, high above the sun's surface. These "prominences" are easily visible along the edge of the sun during the total eclipse. The whispy-thin and incredibly hot outer atmosphere of the sun, called the "corona," is also only visible during totality. So now let's get back to the eclipse!

Three Progressive Eclipse Photos

First Contact

The moon is up there in the sky too; you just can't see it during the day of the eclipse because the lit side is facing away from us (a phase called "New Moon") and the blue sky washes everything out. As the moon just "touches" the sun (actually coming between, us and the sun, not touching!) you see the first bite taken out of the edge of the sun's disk. This is called "first contact." This is where the partial phases of the eclipse start.

For about the next hour and a half the moon covers more and more of the sun's disk. As the total phase of the eclipse approaches, the lighting around you becomes very strange. It gets much darker, but unlike at sunset, the color of the remaining light does not become orangish and reddish. It just gets grayer. If there are animals around to observe, the daytime animals become quiet and prepare for sleep, while at the same time the nocturnal animals get ready to come out. This must be a very confusing time for them because their internal biological clocks must be telling them it's still daytime!

When only a sliver of the sun is left, with only a few minutes to go until totality, you might notice long, straight bands of shadows moving across the ground. These "shadow bands" form from refraction, or bending of light in the earth's atmosphere similar to what you might see on the bottom of a pool of water. This is the same thing that causes stars to twinkle. With the sun only a long slit of light, the distortions in the atmosphere become visible as moving bands, parallel to the remaining slit of sunlight. They are usually very low in contrast and it helps to spread a white sheet on the ground to help viewing. They are VERY difficult to photograph. We've never seen any pictures of shadow bands. Of course, this could be because everyone has their cameras trained on the main event about to happen which is, admittedly, much more spectacular.

Diagram: Contact Series
First, Second, Third, Fourth contact


Second Contact

Second contact occurs when the moon completely covers the sun. Now the action really heats up! The edge of the moon is not perfectly round. There are mountains and valleys that make the edge less than smooth.

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