New Delhi: A surya grahan or solar eclipse is one of the most striking astronomical events visible from earth, yet it does not occur every month. This
often surprises people, especially since the moon completes its orbit around earth roughly every 29.5 days. Each of these cycles includes a new moon, the essential phase required for a solar eclipse to occur. Logically, it may seem that the sun should be blocked just as frequently. However, the reality is more complex. The moon’s orbit is not perfectly aligned with earth’s path around sun.
Instead, it is tilted slightly, and this small difference prevents the precise alignment needed for an eclipse in most months. Only under specific geometric conditions does the moon move directly between earth and sun in a way that casts a visible shadow. These rare alignments happen during limited periods each year, which is why solar eclipses remain occasional and eagerly anticipated celestial events rather than regular monthly occurrences.
Science behind solar eclipse rarity
What creates solar eclipse
A solar eclipse occurs when the moon passes directly between earth and sun during a new moon. If the alignment is exact, the moon blocks part or all of sun’s light, casting a shadow on earth. This alignment must be extremely precise for the eclipse to be visible.
5-Degree tilt that changes everything
The moon’s orbit is tilted by about five degrees compared to earth’s orbit around the sun. Because of this slight angle, the moon usually passes a little above or below the sun during new moon, meaning no shadow falls on earth and no eclipse takes place.
Role of orbital nodes
The moon’s orbit intersects earth’s orbital plane at two points known as nodes. A solar eclipse becomes possible only when a new moon occurs close to one of these nodes. If the new moon happens away from these crossing points, the necessary alignment does not occur.
Eclipse seasons: Limited window
These favourable alignments happen during short intervals called eclipse seasons, which occur roughly every six months and last a little over a month. Only within these windows can the geometry line up precisely enough for a solar eclipse.
Why they feel even rarer
Although several solar eclipses may occur globally in a year, each one is visible only from a narrow path on Earth’s surface. Many regions may wait years before witnessing one, which adds to the perception that they are extremely rare.
Solar eclipses depend on more than the moon’s monthly cycle. A careful balance of tilt, timing and position ensures that the sun’s brief disappearance remains a rare and remarkable spectacle in the sky.
