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Zodiacal lights or False Dawn

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Zodiacal Light intersecting the Milky Way near Black Mesa, Oklahoma

©iStockphoto.com/Neutronman

Zodiacal lights or false dawn, are rare optical phenomena that occur around sunset and sunrise, usually during early spring and late fall. They occur in the form of a hazy light extending in the skies from the horizon, usually in the shape of a triangle or a pyramid.

What are zodiacal lights?

Zodiacal lights occur when sunlight reflects off tiny space particles. These particles or cosmic dust are considered to be fragments of Jupiter family comets. Jupiter family comets are comets that are found revolving around the Sun in a path between the Sun and Jupiter. These comets have a short revolution period, generally less than 200 years, and have their aphelia – the point where they are farthest away from the Sun – close to Jupiter.

While cosmic dust can be found throughout our Solar system, zodiacal lights have been mostly observed in the zone around the ecliptic plane.

The ecliptic plane is an imaginary plane in space that follows the apparent path of the Sun in the sky. The plane looks tilted to about 23.5 degrees from the Earth’s spin axis. This is because the Earth spins around its axis at an angle of 23.5 degrees.

Because most planets in the solar system also have the same ecliptic as Earth, the Earth’s ecliptic plane is used by astronomers as a reference point for observing the planets and many constellations. Constellations that fall within the ecliptics are known as zodiac constellations.

Solar eclipses occur when a new moon aligns with the ecliptic plane, while a lunar eclipse occurs when a full moon aligns with the plane.

When and where to see zodiacal lights

Zodiacal lights are rare and can be observed around the Spring and the Fall Equinox at higher latitudes, and throughout the year in tropical regions.

Those in the Northern Hemisphere are the most likely to see these lights after sunset during spring in the western sky, and in the eastern sky before sunrise in the fall months.

People in the Southern Hemisphere, on the other hand, have the best chance of viewing these lights in the eastern sky after sunset during their fall months, and in the western sky before sunrise during spring.

Bright lights, artificial or natural, and air pollution are the biggest enemies of zodiacal lights watchers. Because these lights are very faint, any ambient light, even from the Moon, can hide them. The best time to observe these lights, therefore, is two weeks after a new moon.

False dawn

Zodiacal lights have a special significance for practitioners of the Islamic faith. Since zodiacal lights are best observed right before sunrise, they can sometimes be mistaken as the beginnings of dawn. This has implications for devout Muslims who have to pray at specific timings. Prophet Muhammed is known to have used the zodiacal lights to define the times of daily prayers.

It is thought that the term False Dawn was coined by Persian poet Omar Khayyám in the 12th century.

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