Representative image of moon.
Credit: X@BenStiller
The full moon has always been an object of serenity associated with charm for poets, literati, and even laypersons. When it loses lustre and presents a night, though temporarily, melancholic thoughts creep in, as penned by various poets and philosophers of the past. This act of the full moon shying away from light, the eclipse, is looked upon as a bad omen, unfortunately.
The inquisitive minds of the past washed off such ideas and eagerly looked forward to the eclipse for a closer understanding. It is the best demonstration for establishing the spherical shape of the Earth. The duration of the eclipse itself is a measure of the extent of the shadow and, therefore, the distance to the moon.
The meticulous follow-ups over centuries revealed two periodicities—one of 176 days and another of 18 years and 11 days. Today, we have the answers in our textbooks.
The earth casts a shadow just as any solid body would do; however, a screen is essential to ‘see’ the shadow. There is no such screen in the sky, but we would see it when another object, such as the moon, passes into the shadow. Though the Earth is opaque, the atmosphere surrounding it can do many tricks with sunlight. It lets some tiny fraction of the light reach the moon. It scatters the white light—different colours into different directions—directing the red onto the moon in the shadow. Some orange and yellow also sneak through, making the moon look colourful before it turns pale.
The shadow is not as well defined as you would see that of an object held in candlelight. The eclipse commences when the moon enters the penumbral shadow. But the change in its brightness is barely noticeable. The show is for everyone; no prior knowledge of telescopes is required.
The colour of the moon during a total eclipse, when it is in the umbra, tells us about the Earth’s atmosphere. For example, a volcanic eruption just before the eclipse fills the atmosphere with thick gas and dust, making it less transparent. The moon will become so dull that it may be impossible even to locate it.
September 7 offers an excellent opportunity to witness this show by the moon. The routine red-orange moon (generally restricted to rising) will have a second show at midnight. By about 10.30 pm, one can see the edges fading; by 11 pm, an orange tint appears. By midnight, it turns pale. What will be the colour? Copper? Orange? Brown? Or just dark and barely visible? Let us watch and verify that it is not ‘bloody’. Should we miss this, the next opportunity would be only the last day of 2028!