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October 2005 Feature: Two Eclipses & Mars Closest to Earth

October 3rd Annular Eclipse of the Sun

The October 3rd annular eclipse starts in the early morning to the northwest of Spain in the North Atlantic Ocean, then travels southeast through Portugal and Spain, and then through Africa. Though the annular eclipse path is lengthy, it's not a lot more than 100 miles wide. (See map.) The partial phase of this solar eclipse, however, encompasses a much larger portion of the globe and can be seen from almost all of Africa and Europe. This map and animation help you to envision the wider scope of this eclipse. A wealth of information on the October 3rd annular solar eclipse is available at Fred Espenak's incomparable eclipse page.

Unlike a total solar eclipse -- where the Moon completely covers over the Sun's disk -- an annular solar eclipse finds the Moon is too far away to totally eclipse the Sun. Hence, in this scenario a ring -- or annulus -- of sunshine encircles the new Moon.

In fact, if the orbits of the Earth around the Sun, and the Moon around the Earth, were perfectly circular, all central (non-partial) solar eclipses would be annular, since the Moon would be too far from us to totally cover the Sun. The elliptical (oblong) orbits of the Earth and Moon, however, assure us that both annular and total solar eclipses happen, given that the Sun's distance from Earth varies by some 3 million miles during the year, and that the Moon's distance from Earth can vary by some 30 thousand miles in a single month.

We are closest to the Sun in early January and farthest in early July. Therefore, it's hardly surprising that annular solar eclipses are more common in December, January and February (when the Sun is nearer to Earth) and that total eclipses come more often in June, July and August (when the Sun is farther away).*

Since the Moon is receding from Earth at about 3.8 centimeters or 1.5 inches per year, it's forecasted that all annular (and no total) solar eclipses will be in store for the far distant future. How far distant? According to Jean Meeus (pages 127-128 of More Mathematical Astronomy Morsels), it'll be somewhere around 1.2 billion years from now! However, the author warns us that this figure presupposes the Moon receding from the Earth at a constant 3.8 meters per century, which he views as doubtful.

October 17th Partial Eclipse of the Moon

Much of the world that misses this month's solar eclipse will get to see the October 17th partial lunar eclipse. Western North America, eastern Asia, Australia, New Zealand and the Pacific get to watch the nearly hour-long show in its entirety. In North America the eclipse happens in the early morning hours before sunrise; whereas in Australia and Asia, this eclipse is seen in the evening after sunset. New Zealanders see the eclipse late at night, and in Alaska and Hawaii, the eclipse happens a few hours after local midnight. This map and site elaborate.

May the reader be forewarned. This is an extremely shallow umbral eclipse, with only the southernmost portion of the Moon dipping into the Earth's dark shadow (umbra). Even at mid eclipse, almost all the Moon resides in the penumbra, the very light shadow surrounding the umbra. This map shows you the Moon's position relative to the umbra (dark shadow) and the penumbra (light shadow).

Yet, it may thrill you to know that this is the very first umbral eclipse of saros series 146. Every 223 lunar months (223 returns to full Moon), there will be another umbral eclipse, till the final umbral eclipse of this saros series comes to pass on June 12, 2997. For an explanation of the saros cycle and its significance, you are invited to click here and here.

Mars Comes Closest To Earth

Throughout October, our faster-moving Earth closes the gap between itself and slower-moving Mars. Earth will lap Mars on the night of November 6-7, passing right between the Sun and Mars. This celebrated event is called an opposition, because the red planet is then opposite of the Sun in our sky, rising in the east at sunset and setting in the west at sunrise. Oppositions of Mars recur in a mean period of 780 days (2 years and 7 weeks).

At or near opposition, Earth comes closest to Mars, and the red planet, in turn, shines most brightly in our sky. In fact, if the orbits of Mars and Earth were perfectly circular, and if both these planetary orbits resided on the same plane, Mars and Earth would always be nearest to one another right at opposition. As it is, Mars comes closest to Earth this year on the night of October 29-30, a solid week before Mars reaches opposition.

Furthermore, if the orbits of Earth and Mars were perfectly circular, Mars would be the same distance from Earth at every opposition. However, since Mars has an highly elliptical (oblong) orbit, Mars' distance from the Sun varies by over 26 million miles throughout the Martian year. When Mars is at opposition and also near perihelion (Mars' closest approach to the Sun) -- as it was in August of 2003 -- the Martian opposition is especially close. On the other hand, if a Martian opposition coincides with aphelion (Mars' farthest distance from the Sun), the opposition is especially far out -- meaning distant. (This map of Mars' last 5 oppositions and orbit of Mars animation help to illustrate.) The most favorable oppositions are in late August and early September, whereas particularly distant ones occur in late February and early March.

Though Mars this time around doesn't match its historically close encounter on August 27, 2003, this year's showing is still a dandy. Mars will shine at its biggest and brightest until the year 2018. For a table listing the dates of Martian oppositions and distances, click here. For a much more detailed page on Martian oppositions, plus a table listing both the dates of oppositions and Mars' closest approaches to Earth, click here.

copyright 2005 by Bruce McClure

* page 70 of More Mathematical Astronomy Morsels by Jean Meeus

September 2005 Feature * November 2005 Feature

Halloween 2005: Arcturus, Ghost of Summer Sun

Past Eclipse Features:

April 2005: Jupiter at Oppostion & A Tale of Two Eclipses
October 2004: Total Eclipse of the Moon
October 2004: The Saros Eclipse Cycle
November 2003: November 8th Total Lunar Eclipse
May 2003: Total Eclipse of the Moon
May 2003: The Saros Eclipse Cycle

Past Mars Features:

August 2003: Mars's Hype & Hoopla
August 2003: Kepler & Mars
November 22, 2003: Mars and the Star 90-Phi Aquari