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'Tis the season to look for eclipses

What season is it? Eclipse season! Yes, we are in one of two eclipse seasons that occur each year, and there will be a total eclipse of the sun Thursday. It will not be visible from Utah, but some Utahns will enjoy it by traveling to places where the shadow of the moon sweeps along the surface of the Earth.

The total eclipse will begin on Earth as the moon's shadow touches Earth in the middle of the Pacific Ocean, then races across 3,500 miles of water in about 11/4 hours to touch land in the Gallapagos Islands. Then it will cross more water to reach the junction of Central and South America, cross the southern tip of Panama, northern Colombia and northwestern Venezuela, move out into the Caribbean Sea where it will fall on several islands including Aruba and Curacao. The shadow will then trace another long stretch of water to reach the Leeward Islands, move out across the Atlantic and finally leave Earth as the sun sets west of the Canary Islands.For a moment, let's understand why the eclipse will occur Thursday. We are in an eclipse season, but what does that mean? We know that Earth glides along in a great annual orbit around the sun, held to the star by the force of gravity existing between the two bodies. Twice each month there is an approximate alignment between sun, Earth and moon: When the moon stands nearly between Earth and sun, we have a new moon and when it is on the other side so that Earth is nearly between sun and moon, the moon is full. It is at the time of new moon that we might have an eclipse of the sun, and when the moon is full, it might be eclipsed in Earth's shadow. Why, then, do we not have eclipses each month?

The answer is, of course, that the three bodies do not quite line up at most new and full moon times - they nearly do, but not quite. This is because the orbit of the moon around Earth is tilted to the plane of Earth's orbit around the sun. Thus, at most new moons the moon passes either above (north) or below (south) of our line of sight to the sun, and at most full moons the moon passes north or south of Earth's shadow.

There are two places along the lunar orbit where the moon cuts through the plane containing Earth and sun. Twice, each month, then, the moon crosses through this plane, and this is usually not at new or full moon times. Being on Earth moving round the sun, we see the sun appear to change its place around the heavens, moving through the constellations of the zodiac, in an apparent annual orbit. This is, of course, a matter of perspective. If we were to observe Earth from the sun, we would see Earth move in this pathway, but being on Earth it is the sun that seems to change and it is this apparent change that causes the seasons.

From our perspective, then, the sun seems to change in our sky and twice each year it reaches one of the points where the moon's orbit intersects the plane of Earth's orbit. These two times are the eclipse seasons, the times that eclipses of sun and moon can occur. All we need during one of these seasons when the sun is at one of these crossover points is to have a new moon or full moon take place then. If it is a new moon at one of these seasons, we will experience an eclipse of the sun. If it is a full moon, we will see the moon go into eclipse. It is possible to have both types of eclipses during an eclipse season. It is even possible to have three eclipses during one eclipse season, two solar eclipses and a lunar one. For this to happen we must have new moon at the beginning of the eclipse season, full moon will occur at the middle of the season and we might have another solar eclipse at the very end of the season. Not all of these eclipses, however, can be total eclipses.

During the eclipse season we are currently in, there are actually two eclipses, but one of them is a lunar eclipse where the moon only slips part way into the partial shadow cast by Earth, the so-called penumbral shadow. This penumbral lunar eclipse will not be much to see: only a slight darkening of part of the moon. It occurs on March 13.

The more interesting eclipse of this eclipse season is the one taking place Thursday, a really nice alignment of sun, moon and Earth that will cause a total solar eclipse for those able and willing to travel to where it can be seen. For up to four minutes, depending on where one is along the eclipse path, day will turn to night and present some of the most glorious sights ever seen by human eyes.

There is so much to see during a total solar eclipse, and this is especially true for this one. Remember the grouping of planets we recently had in the southwest evening sky? That massing of planets still exists, but some of them have moved into the glow of the sun. During the total phase of the eclipse, however, it will be possible to see them: Brilliant Venus will be about 42 degrees west of the sun; Jupiter and Mercury, both very close to the sun, should be visible; dim Mars will be off to the east of the sun and brighter Saturn will be still farther east. In addition to the planets, it should be possible to see several bright stars. The primary feature that everyone will be oohing and ahhing about will be the sun itself, or rather the part of it that will be visible when the brighter solar disk is covered. The wonderful corona will flare out into the sky around the black hole left by the mask of the moon. Having seen several total solar eclipses before, I will not even attempt to describe this. I will only say that one has to see it to believe it. The quality of light combined with the textures of the outer gaseous solar layers, the cooling of the air and the reaction of all living things in the area present a degree of beauty and excitement that can not be adequately put into words.

Yes, I have seen several total solar eclipses before, and I will travel in hopes of seeing this one. Each time I have been so busy taking pictures that afterward I have felt that I had been somehow cheated from experiencing the phenomenon. So, this time I have vowed that I will stand and look around, attempting to more fully comprehend what it means to be in alignment with the greatest bodies of our sky. I made this vow once before, but as the event approached, I weakened. I said to myself, "I will just take a few photographs," but I found myself even changing lenses during the totality, and once again felt that I had shortchanged myself in trade for getting memories on film. This time I will remain true to my vow and let others with bigger and better equipment take the photographs. I, for one, hope to observe one of the most captivating of all phenomena we ever see on Earth: I will watch the delicate pearly corona; I will see brilliant pink prominences at the edge of the solar disk; I will look around at the planets and bright stars; and I will take a moment to enjoy the expressions bubbling out of other people around me, many of them clicking shutters. During those three minutes I might even be able to hear and see reactions from wildlife in my vicinity as they, too, sense the mysterious moment when night comes during the middle of the day. Of course it might be cloudy, but even if that occurs there will be things to experience standing in perfect alignment: sun, moon and me on that particular little plot of Mother Earth.