Driftless Dark Skies: Halfway for Halley

2061 sky view graphic created with Starry Night software. Orbit graphic by Ian Ridpath.

Driftless Dark Skies: Halfway for Halley

Humans have been awed by Comet Halley for generations. Every 75-79 years it returns and is visible to skywatchers on Earth. There is a special event in its journey to mark this month. On Saturday December 9, Halley will reach its greatest distance from the Sun (aphelion) and will slowly turn and move closer to Earth.

We won’t be able to see this event, but it’s easy to imagine. Picture a ball of rock and ice 5-9 miles in diameter and 3 billion miles distant orbiting at 2000 mph. That’s beyond the orbit of Neptune and in the frozen realm of the Kuiper Belt with Pluto, Haumea, Makemake, Quaoar, Orcus and so many other worlds. It’s so distant that the sunlight reflected by Comet Halley takes almost five hours to reach us. Even our best telescopes won’t spot it. At magnitude 34.7, it’s 15 million times dimmer than the faintest star we can see with our unaided eyes.

All the same, I am encouraging skywatchers to head out the second weekend of December and look towards Halley. It will rise in the east around 9pm and be about ten degrees (one fist held at arm’s length) below and to the left of the bright star Procyon. Take time to remember previous visits of Halley and imagine the future ones. I would love for folks to share their memories of seeing the comet in 1986 and what they think it will be like in 2061.

For most of us, the sight of Halley’s Comet is a once in a lifetime experience. Except for the fortunate cohort of GenXers who could have seen it as youths in 1986 and may again as elders in 2061. Its orbit of ~76 years is a bit more than the three score and ten of the psalm and average human life expectancy. Seeing this comet puts us in the good company of the hundred generations of skywatchers who have been observing and recording it for over two millennia. But we are brightening our skies at 10% a year with artificial light at night. If we do not make smart lighting changes, the skywatchers of 2061 will be the first generation unable to see and greet Comet Halley for themselves.

Comet Halley will be closest to the Sun (perihelion) and Earth on July 28/29, 2061 when it orbits by at a speed of 120,000 mph. It will be visible in the twilight sky of summer as it passes below the Great Bear in the northwest following a path similar to Comet NEOWISE in July 2020. Halley is predicted to be three times brighter than NEOWISE and ten times brighter than it was in February 1986. It may be at its best August 4-8 when no moonlight brightens the sky, and it appears above dazzling Venus in the west.

It is possible to see bits of Comet Halley as we await its return. As comets orbit the Sun, they leave a debris trail of dust and rock behind them. Earth crosses this trail twice a year, and we see pieces of Halley briefly lighting up the sky as meteors. In 2024, these will peak as the Eta Aquariid shower on May 5/6 and the Orionids on October 20/21.

Comet Halley will be even brighter (5X) in 2134 when it passes within 9 million miles of Earth on May 7. But why care about an astronomical event that we may not live to see? Because we know people who will. One of the many things I love about stargazing is how it encourages us to consider deep time and motivates us to be good ancestors. Like some of you, I have known and spoken with people born in the nineteenth century who remembered that “there once was a sky full of stars” even in urban areas. Now I meet and educate young people who will be alive in the twenty-second century. I like to tell them how my great-grandfather was there to see Halley in 1910, how so many of us saw Halley’s Comet in 1986, and how they should watch for it in the summer of 2061. But when it returns, we need our skies to be dark enough for them to be awed. And we want them dark enough for their children and grandchildren to be wowed by Halley’s Comet in 2134. Until then, Happy Halfway for Halley Day!

 

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. He volunteers with NASA/JPL as a Solar System Ambassador , with the International Dark-Sky Association as an Advocate, and the International Astronomical Union as a Dark Sky Ambassador. For more information about stargazing in southwest WI, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies.