Time Seeds of Universe- 4
There was a Solar Eclipse in June 2020, and its path crossed Delhi. While I was slowly learning astronomical concepts, understanding the science of eclipses was awe-inspiring. Earth, Sun, and Moon are all in motion—orbiting, wobbling, and rotating, with their axes also experiencing precession.
Nothing in this universe is static. Everything is constantly in motion, taking various forms, and there is an order to that movement. However, do these celestial objects literally cross paths in the sky? Not in a physical sense, as their intersection would lead to dissolution! Instead, there is an alignment of celestial objects with respect to a reference frame, where one object appears to be blocked by another from the observer’s perspective. The universe must be filled with such alignments occurring every moment, somewhere in the deep sky for an observer sitting at the far edge of the celestial sphere!
Returning to Earth, what are eclipses? Eclipses are fascinating events that occur in the sky, changing how we perceive two of the biggest celestial objects—the Sun and the Moon—from our vantage point on Earth. For an observer on Earth, eclipses happen when the Earth, Sun, and Moon align almost in a straight line. In astronomy, the term “syzygy” is used to describe the almost straight-line configuration of three or more celestial bodies. During syzygy, two types of eclipses occur—Solar Eclipse and Lunar Eclipse. A Solar Eclipse happens when the Sun is eclipsed by the Moon, while a Lunar Eclipse occurs when the Moon is eclipsed by the Earth.
Solar Eclipse
A Solar Eclipse occurs during a new moon when the Moon comes between the Earth and the Sun while the three are in syzygy (Sun-Moon-Earth). It is as if the Moon gets in the way of the Sun’s light and casts its shadow on Earth. This phenomenon results in darkness during the day, and the Moon’s movement over the Sun becomes visible from Earth. This is known as a total solar eclipse.
Why don’t we see a solar eclipse during every new moon? The Sun, Moon, and Earth are not in syzygy for every new moon, and the Moon does not cast its shadow on Earth. This is due to the Moon’s orbit around Earth being tilted compared to Earth’s orbit around the Sun, with a tilt of 5.1° with respect to the ecliptic plane. Consequently, not every new moon results in syzygy. Therefore, we only get to see eclipses when the alignments of the three celestial bodies are almost in a straight line. There are three types of solar eclipses: total, partial, and annular, depending on the extent of the Sun’s coverage by the Moon as observed from Earth.
Total Solar Eclipse: A total solar eclipse occurs when the Moon completely covers the Sun, as seen from Earth. Totality during such an eclipse can only be seen from a limited area, forming a narrow belt. This total eclipse happens approximately once every year and a half somewhere on Earth.
Partial Solar Eclipse: A partial solar eclipse occurs when the Moon only partially covers the Sun’s disk. This type of eclipse happens at least twice a year somewhere on Earth.
Annular Solar Eclipse: An annular solar eclipse occurs when the New Moon covers the Sun’s center, leaving its outer edges to form a “ring of fire” or annulus.
But not everyone gets to experience every solar eclipse. Witnessing a total solar eclipse is a rare occurrence. The Moon’s shadow on Earth is relatively small, so only a small portion of the planet gets to see it. On average, the same spot on Earth only witnesses a solar eclipse for a few minutes about every 375 years!
Lunar Eclipses
During a Lunar Eclipse, when the Sun-Earth-Moon align, the Earth blocks the Sun’s rays from directly reaching the Moon. Since the Moon does not emit its own light and its brightness comes from reflecting the Sun’s rays, lunar eclipses only happen during a Full Moon. It’s a play of light and shadow that creates these celestial events. There are three types of lunar eclipses—Total, Partial, and Penumbral—that can be observed from Earth:
Total Lunar Eclipse: A total lunar eclipse occurs when Earth’s umbra, the central dark part of its shadow, covers the entire surface of the Moon.
Partial Lunar Eclipse: A partial lunar eclipse takes place when Earth’s umbra covers only a portion of the Moon’s surface.
Penumbral Lunar Eclipse: A penumbral lunar eclipse occurs when the Moon passes through the faint penumbral portion of Earth’s shadow.
Occultation and Transit
When a planet comes between Earth and the Sun, it is referred to as a transit. Mercury and Venus are the only two planets in our solar system whose orbits lie inside Earth’s orbit, allowing them to be seen transiting the Sun from our perspective on Earth. Two examples the recorded transits in recent time areTrasit of Venus as seen from Earth, 2012 and The Moon transiting in front of Earth as seen by Deep Space Climate Observatory on 4 August 2015. Studying eclipses and celestial events offers a profound appreciation for the dynamic and interconnected nature of our universe.
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Time Seeds of Universe is a series on understanding time. ‘TimeSeeds of Universe: Path, Light, and Shadows‘ is part 4 in this series. Following are the link to other blogs of this series :
Time Seeds of Universe-1 : A Journey of Self-Discovery
Time Seeds of Universe- 2: It is about Reference Frame
Time Seeds of Universe- 3: A Sphere with Infinite Radius
Time Seeds of Universe – 5: Quest for Salvation in the Wonders of Nature
