One of the most spectacular sights to behold once every 18 months, solar and lunar eclipses are fascinating to the human eye. However, a total solar or lunar eclipse would occur only once in 50-80 years. Depending on where you are located on Earth, some locations are like a diamond box in a Cricket stadium that enables you to view a total eclipse in all its glory. When people observed the Moon during an eclipse, they saw the Earth’s shadow on the Moon, which led to the discovery that the Earth was round.
Scientists still continue to discover more about the Moon from lunar eclipses. In 2011, NASA’s lunar reconnaissance orbiter obtained data of how instantly the Moon’s dayside cools during a lunar eclipse. This helped scientists understand the Moon’s surface better. Also, solar eclipses pave the way for astrophysicists to learn more about the Sun’s corona, its top layer.
Both the solar and lunar eclipses depend on the position and movement of the Earth and the Moon while orbiting the Sun. The Moon obstructs the Sun’s rays during a solar eclipse, and its shadow falls on Earth. In a lunar eclipse, the inverse happens, where the shadow of the Earth falls on the Moon, causing it to appear red. Come, let’s dive into the principle of eclipses and how they occur.
How Does the Moon Revolve Around the Earth?
To understand the cause of Eclipses, we need to understand how the Moon orbits the Earth. If you are an avid sky gazer, you might notice that the Moon keeps the same side facing our planet. This is because the Moon is tidally locked to our planet as it orbits. Most planets that are relatively close to each other in orbit are tidally locked in orbit with synchronized rotation. For instance, the planet Mercury is tidally locked to the Sun due to its close proximity and the enormous gravitational force and mass of the Sun.
The Moon orbits Earth with a 5-degree tilt; its orbit determines the portion of the Moon that is visible to the Earth. For instance, if the Moon reaches point B in the image below, then it would appear crescent-shaped when viewed from the Earth. This is because the side of the Moon exposed to the Sun is only faintly visible from Earth, thereby appearing as a crescent. The same principle applies to half-crescent, half-moon, and gibbous Moon. The whole cycle of the Moon’s orbit around Earth is 27.5 days, approximately 28 days.
What is a Solar Eclipse?
Now that we know how the Moon revolves around our Earth and how its orbit impacts our perception of it, it would be easy for us to understand how solar eclipses occur. When the Moon orbits Earth, its orbit also traverses between the Sun and our Earth. At this moment, our Moon blocks the sunlight that reaches us and results in a solar eclipse. The Moon casts a shadow onto Earth.
As the Moon obstructs the Sun’s rays, its shadow gets smaller as it reaches Earth. Umbra is the dark centre of the Moon’s shadow. People who are witnessing a total Solar Eclipse will be standing in the umbra. Penumbra is the lighter outer part of the Moon’s shadow. People who stand in the penumbra will only see a partial eclipse due to the outer shadow. A total solar eclipse is an umbral eclipse, and a partial solar eclipse is known as a penumbral eclipse. A perfect total solar eclipse will look like a ring as the Moon obstructs the Sun’s rays. Since the Moon is smaller than the Sun, the outer portion of the Sun’s rays would seep through the Moon’s edges, making it appear like a beautiful ring studded with a precious gemstone.
A total solar eclipse usually occurs in certain parts of the globe that are perfectly positioned under the umbral shadow of the Moon. They occur once in two years, and people in certain locations could be fortunate enough to see total solar eclipses more frequently than others due to their proximity to the umbra. Unlike lunar eclipses, solar eclipses last for a few minutes. If you plan to see the Sun during an eclipse, think again, as the Sun’s harmful rays could damage your retina badly, causing permanent blindness. Make sure to use solar viewing goggles or a solar viewer to enjoy the show.
What is a Lunar Eclipse?
As Earth’s natural satellite, Moon governs many aspects of our planet, from marking festivals to affecting tidal currents. When manifesting as a Full Moon, the cold, rocky body comes directly opposite to the Sun. When the Earth comes between the Sun and the Moon, it blocks sunlight from reaching the Moon. This specific alignment casts the Earth’s shadow on the Moon’s surface, causing a total lunar eclipse (the Earth eclipsing the Sun’s light from the Moon). Hence, a total lunar eclipse requires a Full Moon and the straight alignment of the Sun, Earth, and Moon.
Full Moons come around every month roughly. But why don’t we get to see the lunar eclipse every other month? Since the Moon’s orbit is inclined by 5° to the Earth’s orbit around the Sun, it usually passes above or below Earth’s shadows, totally unaffected by them. Only around two to four times a year, the Moon comes in the path of the Earth’s shadows causing either partial or total lunar eclipse (governed by the portion of the Moon affected by the Earth’s shadows).
Well, if the Earth blocks sunlight from falling on the Moon’s surface, how are we still able to see it? Thanks to the bending of light waves, sunlight passes the Earth’s atmosphere and lights up the Moon’s surface. Add to that the dynamics of light- refraction, scattering and absorption, the Moon appears deep red during the lunar eclipse. Unlike a solar eclipse, you don’t need aid to watch the Moon on a lunar eclipse. Your bare eyes will do!
Myths and Superstitions about Eclipses
Humans have always built cultural and religious myths around celestial events – eclipses are not an exception.
• Some believe that solar eclipses produce harmful rays capable of robbing one’s eyesight. But scientists disregard the notion on the grounds that the faint light crossing 150 million kilometres of space can cause, at the worst, retinal damage but not blindness.
• It is widely believed that pregnant women shouldn’t watch the eclipse as its radiation might damage the foetus. Scientists completely dismiss this myth stating that the electromagnetic radiation reaching the Earth from the Sun is perfectly safe.
• Another classic myth is that eclipses will poison any food prepared during the event. Experts suggest not to pay heed to this folklore and keep going about your life as any other normal day.
• A few religious texts strongly recommend against taking baths during the lunar eclipse. Since this is a baseless superstition, please take a bath for the sake of those around, if not for you.
• “You should not sleep during the eclipse,” Indian astrologers point out, considering the event to be a bad omen. Yet, science reaffirms, “You sleeping on your bed has nothing to do with the Moon.”
We might have come far from the ages of folktales and misinformation, but myths and superstitions continue to persist among us. Now that you know how eclipses occur keep looking forward to the numerous eclipses ahead without fear or concern, but only wonder and excitement.
Space Age 