We may sometimes forget that Holi, the festival of colours and spring, is actually defined as the day of the full moon closest to the spring equinox. Yesterday’s Holi was special: the full moon coincided with the equinox, and the moon’s closest approach to the earth happened at the same time. The moon looked spectacular, so I brought out my camera to take a photo. It’d been a long time since I turned a camera at the full moon, so I hadn’t realized how spectacular the result would be. You can see very clearly the dark patches which are lunar plains (fancifully called seas by ancient astronomers), the white spots of craters from which light-coloured lines radiate out, and the mountains and craters along part of the limb. In fact those mountains are high enough that the shape of the moon is not the perfectly round one we imagine.
People walked on the moon in my youth and I eagerly followed their paths in maps of the moon. This photo rekindled that interest. I put down the names of features I could remember: the large craters Tycho (so very visible), Copernicus, Kepler, and Aristarchus, the lowlands (mistakenly called seas and oceans) Tranquility, Serenity, Rains, and Storms, and the Apennines bordering the Sea of Rains. You can’t see the 4.7 Kilometers tall Mount Huygens, the highest visible point on the moon, in the Apennine highlands. You’ll need a better camera to see it.
I’d not kept track of what those Apollo missions of fifty years ago, and the exploration of the solar system by robots since then, taught us about the apocalyptic history of the solar system. A little reading brought me up to date. It seems that the lunar lowlands (seas) were formed by the cooling of magma created by a late heavy bombardment of asteroids around 3.9 billion years ago, when single celled life was beginning to take hold in the seas of the earth. All the inner planets contain scars from this era. Tycho crater, on the other hand, was formed a mere 108 million years ago, when dinosaurs flourished on earth. The astronomical origin of Tycho and the dinosaur-killer which hit earth about 65 million years ago are possibly connected. Spacecraft have opened a new golden age of solar-system astronomy. Discovering that was a wonderful way to close the day of the festival of spring. Happy Holi to you.