Coming in From the Cold…
As many of you know, my interest in astronomy and stargazing goes back much farther than my career at Gateway Arch National Park- in fact all the way back to the space program of the 1960s. Throughout my long avocation as a stargazer, one of my Holy Grails has been the appearance of a “Great Comet”- bright enough to easily see with the unaided eye, with a prominent tail. I was rewarded as a teenager by Comet West, which I could see right through my window in suburban Chicago in March of 1976. Unfortunately, it was a twenty year wait until I could see the next two “Great Comets” in quick succession- Hyakutake in 1996 and Hale-Bopp in 1997. Both were amazing sights. In my opinion, there has not been another comet visible from the northern hemisphere that qualified for the “great” title since then although NEOWISE, in 2020, came close. Therefor my total is just three “Great Comets” in more than fifty years.
Perhaps some of you are thinking, “What about Halley’s Comet?” Halley (I pronounce it Hal-ee) is by far the most famous of comets, having been seen at every chance since 240 B.C., averaging 76 years between returns. There is a slight variation in the orbital period due to the gravitational effects of Jupiter and other planets. The 18th Century British astronomer Edmond Halley was the first to recognize that the recorded visits of several comets over the centuries were multiple returns of the same object. Although he knew that he would not live long enough to see it, Halley predicted that the comet would return in 1758. He was posthumously proved correct, and the comet was named after him. Since it was the first comet whose return was predicted, modern astronomers have given it the official designation of 1P/Halley.
You might possibly have seen some uninformed chatter on the internet about Halley’s Comet returning this year, but that is just about the opposite of the truth. In fact, the breaking news that I can share with you about Halley is that either this month or next (opinion is divided), the comet will reach aphelion- that is its farthest point of the Sun, about 3,300,000,000 miles from us. I expect and hope that the comet will be photographed by the Hubble and/or Webb Space Telescopes and large Earth-based observatories while at aphelion. Even in these instruments, it will appear as no more than an incredibly dim and tiny speck, but it still will be an important moment in history. Thereafter, Halley’s Comet will make the very long journey back following its huge cigar-shaped orbit, spending the vast majority of the time in the lonely and cold outer solar system. Very gradually, the comet will gain speed and brighten, with the pace increasing until finally with breathless speed, it makes its next appearance for Earth based stargazers in the summer of 2061.
To me, as a veteran stargazer, Halley’s Comet was an impressive sight at its most recent visit in 1986, probably fifth or sixth best out of the approximately fifty comets I have seen. Since I knew just where to look, I could easily find the comet. It looked somewhat dim with my unaided eyes from a dark sky location, with a short tail pointing outward that some people thought made it look like an ear swab. My best views took place when I woke up before dawn and traveled out on several mornings in March of 1986. I can’t honestly call it “great”- I had to carefully point Halley out so that others could spot it. Most of these people were a bit disappointed, although very glad that they had the opportunity to see Halley. The view resembled the picture shown below. I took some images quite a bit like this using my old 35mm camera and the old rolled film that you used to load in the dark onto the spools in the camera, but unfortunately I can’t find my own pictures from 1986 anymore.
Halley’s Comet, March 1986. Photo courtesy of European Southern Observatory
I wasn’t surprised at this less than stellar performance because as luck would have it, the geometry of Halley’s 1986 return was probably the worst in 2,000 years. When closest to the Sun and naturally brightest, the comet stood on the far side of our star as seen from Earth. It passed only moderately near our planet well before and after this perihelion. All this caused Halley to remain modestly bright for a long time, but it failed to ever become very bright. It so happens that the geometry of Halley’s 2061 return will be much better, by the way. One of the reasons that there are so few “Great Comets” is due to this geometry, as well as bright city lights and/or moonlight. There is a slim chance that Comet Tsuchinshan-ATLAS, discovered early this year, might put on an impressive show next October, but only time will tell. Comet predictions are based upon their brightness at a given distance from the Sun. However, quite a few comets have seemed to be unusually active and bright at a great distance, only to fall far short of expectations or to even disintegrate as they approach the Earth and Sun. The disappointments caused by Comets Kohoutek in 1974 and ISON in 2013 are forever etched into my mind. If it does look like Comet T-A will put on a good show, you will certainly read about it here, much closer to the event.
Although the parent comet won’t be visible to human eyes for over 37 more years, it is possible to see pieces of Halley every year. The comet leaves debris behind, and twice a year, in May and October, the Earth intersects its orbit, producing the Eta Aquarid and Orionid meteor showers. Unfortunately, neither of these is particularly rich in numbers, which is why I don’t think I have ever mentioned them in this blog before now. If you venture out to a dark sky location and have very clear skies, you might glimpse 10 or 15 meteors an hour from these two showers, if you are lucky. The Perseids of August and Geminids of December are much more plentiful, and rightly get the lion’s share of attention.
While objectively not all that impressive, thinking back on it, Halley’s Comet did produce some great memories for me in 1986. I was an “Astronomy Assistant” at a local college observatory at that time, and we were thronged with guests anxious to see the comet, diminished by city lights and the poor geometry though it was. In order to see Halley’s Comet twice in a lifetime, you need to have all of the “big three”- sufficient length of life, vision, and mind. My own chances of pulling this off this feat are not quite zero but certainly not good, as I will be turning 100 during the next return. In 1985 and 1986, I got to show Halley to a couple of people who had also seen it in 1910. I feel that this was quite an honor, and I also had the privilege of showing the comet to many children who will have that same opportunity in 2061. Maybe, just maybe, they will remember the youngish guy, probably long gone by then, who showed them Halley’s Comet so long ago.
The European Space Agency’s Giotto spacecraft caught this close up of Halley’s Comet during the 1986 return. The small rocky core of the comets is surrounded by dust and ice that vaporizes when the comet is close to the Sun. Courtesy of ESA.
The Gateway to the Stars program is complete for 2023. Monthly telescope viewing sessions combined with Ranger or expert-led sunset programs on astronomy and/or national parks are typically held from May through October. We also expect to present educational programs in March 2024 highlighting the total solar eclipse that will be visible on April 8 from close to St. Louis. One program is already tentatively set for March 23rd. Programs are presented by Gateway Arch National Park and our St. Louis Astronomical Society partners.