Published: 2021-01-13 14:06:00
Updated: 2021-01-18 11:36:41
By Tony Rice, NASA Ambassador
We could all use something interesting to look forward to this year. Astronomer Greg Leonard may have provided just that on January 3, 2021 with the discovery of a comet nearly 440 million miles from Earth.
Based on more than 100 observations in the following days, researchers worked out the orbit of Comet C/2021 A1 (Leonard) which brings it through the inner solar system later this year.
The comet will be at its closest to the Sun (perihelion) a year to the day of its discovery. It will be closest to Earth the evening of December 12, 2021, at a distance of more than 21 million miles.
On paper, this suggests a maximum brightness of 4.18 making it visible from rural areas, However, the comet will be very low on the horizon forcing us to look through much more atmosphere than if it were directly overhead. This will make it appear 6 or 7 times dimmer, even from very dark locations. But predicating the visibility of comets is tricky, especially so far out.
Through the end of December, the comet grow slightly dimmer is it moves away from Earth but it will also appear higher above the horizon making it easier to see in the dusky sky.
It could also grow brighter.
As the comet grows draws closer to the Sun, ice boils off the surface bringing dust and debris with it that can creating a tail hundreds of thousands of miles or more long. As the Sun illuminates the tail it can brighten significantly. Some comets, like NEOWISE last year, also form a second, often blue colored, tail of electrically charged gas.
However that same energy from the Sun which creates that brilliant tail can cause a comet to break apart, something that could happen tomorrow, as the comet nears the Sun, or not at all. As astronomer David H. Levy says, “Comets are like cats: they have tails, and they do precisely what they want.”