Throughout December, a once-in-a-lifetime comet will be visible in the sky for the majority of the month, and is expected to pass closest to Earth on December 12. Comet Leonard, also known as Comet C/2021 A1, was discovered in early January 2021 and is currently on its way to achieving its closest approach to the Sun. The comet, which has a greenish coma, was discovered around the heart of NGC 4631, better known as the Whale Galaxy. With its closest approach to Earth (and even closer approach to Venus) still to come in December, comet Leonard will become brighter on January 3, 2022, whenit is expected to reach the Sun and fly out for a million years. Subsequently, it will become an interstellar comet, leaving our Solar System behind.
On December 12, when the comet will pass closest to Earth, just a few weeks before it achieves its closest approach to the Sun, it is expected to brighten and become visible to the naked eye, according to some estimates. While comets are notoriously difficult to predict, Comet Leonard will be visible a few hours before sunrise across the constellations Coma Berenices, Boötes, and Serpens Caput, low in the east-northeast sky. With a small telescope or a pair of binoculars, it will be easy to spot. As it approaches the horizon, it will pass between Arcturus and the handle of the Big Dipper, right around the time of its closest approach to Earth.
Throughout the month, Comet Leonard is best seen in the early morning before sunrise. To find it, one must look east one to two hours before sunrise. It will climb highest in the sky right before dawn, but the sky will also be lightest at that time. On December 12, go outside at sunset to look for the comet as it passes Venus and Mercury, then Saturn and Jupiter in the southwest.