While totality will mark the crowning moment of the Aug. 21 solar eclipse, several other phenomena leading up to this much anticipated climax will be worth experiencing.
The entire sequence — including the brief appearance of the visually stunning Baily's Beads and Diamond Ring Effect — will be an enchanting, multisensory encounter with one of nature's sublime spectacles.
At the Madras High School football field, where the Lowell Observatory Solar Eclipse Experience will take place, the fun starts at 9:06:42 a.m., when the Moon takes its first bite out of the Sun in a moment called first contact. This signals the beginning of the eclipse, though it initially is barely noticeable.
Using a filtered telescope, solar glasses, or other appropriate observing techniques, observers will soon be able to see a small chunk of the Sun blocked from view by the Moon. This darkened area will gradually enlarge over the 73-minute transition from the partial to total phases of the eclipse.
At about 10 a.m. — 20 minutes before totality begins — the visible part of the Sun will have shriveled to almost a point (rather than a disc), resulting in sharper shadows. Soon, when about 85 percent of the Sun is covered, the sky will have darkened to the point that the planet Venus will be visible with the unaided eye, 34 degrees to the northwest of the Sun. At about 10:10 am, fainter Jupiter will be visible, a little more than 50 degrees southeast of the Sun.
Soon, the darkening sky will make those witnessing the eclipse feel like night is falling, though the darkest part of the sky will be toward the Sun, rather than at the distant horizon. Observers may notice that birds will stop singing and other daytime animals will cease activity, as if night has truly arrived. Just like at actual nightfall, this period of silence might then be followed by the sounds of crickets, cicadas, frogs, and other nocturnal critters. The temperature will also drop, perhaps up to 15 degrees.
At about 10:19:32 a.m. — two seconds before totality begins — a few rays of the Sun will shine through valleys and other irregularities on the lunar limb (the edge of the Moon, as seen from Earth), resulting in several bright globules of light called Baily's Beads.
This feature is named after English astronomer Francis Baily, who in 1836 explained the nature of the phenomena. As with many instances in science, Baily was not the first person to observe or explain the effect; that honor goes to Baily's countryman Edmond Halley (namesake of Halley's Comet) in 1715.
The beads will be visible for only a couple of seconds. The last one glows brightly and looks like the diamond on a ring; it is thus called the Diamond Ring Effect. Totality begins at 10:19:34, a moment designated as second contact.
During totality — and only during totality, when the Sun is completely blocked from view by the Moon — observers can (and should) remove protective eyewear and safely look directly toward the blotted-out Sun. A bright halo will surround the dark, spherical form of the Sun. This halo is the solar corona — the Sun's outer atmosphere — and is not visible except during total solar eclipses or by using specialized instruments.
Viewing the totally eclipsed Sun can be mesmerizing, but observers should also take a few moments to glimpse Earth's horizons. They will all display sunset colors in what astronomers call a "360 degree sunset." Totality will end at 10:21:36 (third contact) when the Sun begins to emerge from behind the Moon.
During the exciting buildup to totality, observers might miss some of the features described above. Luckily, the Diamond Ring and Baily's Beads will reappear, in opposite order, when totality ends and the Sun is again only partially eclipsed. The Moon will eventually move completely past the Sun and the eclipse will end at 11:41:03 (fourth contact).
The Aug. 21 total solar eclipse will be a perfect opportunity to learn about the workings of the universe around us, as well as a rare opportunity to witness a stunning natural phenomenon that is truly the stuff of legends.
To make the most of the experience, observers should consider attending events such as the Lowell Observatory Solar Eclipse Experience at the Madras High School football field, where professional scientists and educators will explain the science behind such cosmic events. See www.lowellsolareclipse.com.