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Monday, January 16, 2017

Eclipses: Do you Know the Difference?


Students are familiar with the words solar and lunar. Solar refers to the Sun and lunar refers to the Moon. We understand what is meant by "solar energy" and "lunar landings" but we may not have a clear understanding of the difference between a solar eclipse and a lunar eclipse. You need to understand the difference before you take a quiz next week.

A lunar eclipse occurs when the Earth passes between the Moon and the Sun. The Earth's shadow blocks the moon completely or blocks a portion of it. Keep in mind that we are able to see the Moon because it reflects the Sun's light (refulgence). The Moon's albedo is 0.136, meaning that only 13.6% of sunlight incident on the Moon is reflected.

A solar eclipse occurs when the Moon passes between the Earth and the Sun, blocking all or a portion of the Sun. A solar eclipse can be total or partial. Wesleyan students can view a total eclipse of the Sun on August 21, 2017 if you go to the part of North Carolina shown on this map:

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You must be in the path shown between 2:00 and 2:30 pm in order to see the total eclipse of the Sun! This is a narrow path of only 43.6 miles in North Carolina. Hopefully, the weather will be clear. Please wear protective eye gear while viewing the eclipse.

Sometimes a solar eclipse is annular, that means that only the edge of the sun is visible as a ring of fire around the moon. Annular solar eclipses take place when these conditions exist:
  • The Moon is a new Moon.
  • The Moon is at or near a lunar node.
  • The Earth, Moon and Sun are perfectly aligned in a straight line.
  • The Moon is at its apogee.
The next annular solar eclipse will take place on February 26, 2017 and, weather permitting, it will be visible from a narrow path stretching from the southern tip of South America to southern and western Africa.

Related reading: Opposition Surge; The Great Solar Eclipse of 2017

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