From a historic midsummer total solar eclipse that swept across the United States to wonderful evening apparitions of Venus and Saturn to great performances by two of the best annual meteor showers, this year has been a good one for amateur astronomers.
Here's Space.com's look at the top skywatching highlights of 2017.
Eclipses
The big story of 2017, of course, was the "Great American Eclipse." Those living within a path roughly 70 miles (113 kilometers) wide and stretching from coast to coast across the United States got an opportunity to observe nature's greatest show — a total eclipse of the sun.
This was the first total solar eclipse visible from the contiguous (Lower 48) states since 1979. (Alaska had its turn in 1990 and Hawaii got one in 1991). In addition, the shadow track — better known as the "path of totality" — swept over just the United States (and no other country) for the very first time in modern history. [Amazing Photos of the 2017 Total Solar Eclipse]
Thankfully, the weather pretty much cooperated for most viewers along the eclipse path. Problematic weather in the form of overcast skies and scattered rain showers existed over parts of the central Great Plains, as well as along the coast of South Carolina. But almost everywhere else, the skies were pretty clear, and eclipse watchers young and old were not denied their spectacle.
A CNN poll indicated that about half of all Americans watched some part of the eclipse. About 12 million people lived in the path of totality, which stretched from Oregon to South Carolina. As to how many actually experienced totality, we can only make educated guesses. One estimate made in advance of the eclipse predicted that 2 million to 7 million people who lived within a day's drive of the path of totality would make the trek to see it. But in the aftermath of the event, there were suggestions that even 20 million was a very conservative estimate for just how many people experienced totality in person.
Then there was online viewing. NASA reported that 4.4 million people were watching at the midpoint of its eclipse webcast, making the eclipse the most-viewed event in the agency's history. And a September study estimated that about 215 million American adults — nearly 90 percent of the nation's adult population — watched the eclipse in some fashion.
Perhaps the most interesting statistic from CNN's poll found people's excitement about the eclipse to be consistently inversely correlated with age. Some experts likened the event's potential to inspire young people to that of the Apollo moon landings.
Ring of fire
About six months earlier, on Feb. 26, a different type of solar eclipse took place — an annular eclipse, in which the dark silhouette of the moon appeared ever-so-slightly smaller than the disk of the sun. The narrow eclipse path began in the South Pacific at sunrise, crossed Patagonia and then swept across a broad expanse of the South Atlantic before sweeping over three African countries.
A partial solar eclipse of varying extent was visible from the lower two-thirds of South America, southern and western portions of Africa and much of Antarctica.
In some cases, both the moon and local clouds took turns hiding the face of the sun. From Santiago, Chile, for instance, Patricio Leon commented, "The clouds had no mercy … but eventually a small clearing revealed the eclipse." In all, about 500 million people worldwide got a chance (local weather permitting) to view the eclipse. [The 8 Most Famous Solar Eclipses in History]
Shady little dramas
There was also a lunar eclipse on Feb. 10, but by normal standards it was somewhat underwhelming. This one was a "penumbral" eclipse: The moon passed through the pale outskirts of our planet's shadow (the penumbra) rather than directly through its much darker core (the umbra). At maximum eclipse, nearly 99 percent of the moon was immersed in the shadow, resulting in the upper half of the moon appearing noticeably shaded or smudged. Observers on every continent except Australia witnessed the shadow, if they cared to look.
Two weeks before the Great American Solar Eclipse, on Aug. 7, there was what could have been called the "Old World Lunar Eclipse." This event was visible exclusively from the Eastern Hemisphere, running east from much of Europe and Africa through Asia, Australia and New Zealand. The moon slipped partially through the northern part of the Earth's dark umbra, producing a dark "bite" covering roughly one-quarter of the moon's diameter on its lower limb. Wherever skies were clear, the full moon grazed the shadow of our planet for nearly two hours, giving skywatchers a leisurely view of the event.
Eclipses of a different kind
Sometimes the moon will cross paths not with the sun, but rather with a bright star. In 2017, North Americans could watch the moon eclipse or "occult" two of the 21 brightest stars in the sky.
On March 4 and again on Nov. 5, the moon passed in front of Aldebaran, the bright orange star marking the angry eye of Taurus, the Bull. And on Oct. 15, Regulus, the brightest star in Leo, the Lion was covered by a slender crescent moon before sunrise as seen from the United States and most of the Caribbean. On the year's penultimate day (Dec. 30), the moon will have a final rendezvous with Aldebaran in the North American early evening.
Meteor showers
2017 was a good year for two of the top three annual meteor showers. On Jan. 3, Earth passed through a stream of dusty debris from the shattered comet 2003 EH1, the source of the annual Quadrantid meteor shower.
Forecasts suggested that this year's shower would favor western parts of North America and islands across the Pacific. But, based on observations collected worldwide by the International Meteor Organization (IMO), the peak of the "Quads" came about 4 hours earlier than expected, giving those in Eastern North America the best views. Observers positioned under favorably dark skies could count nearly 80 meteors per hour.
Unfortunately, the moon was just past full when the peak of the popular Perseid meteor shower occurred on Aug. 12. For every bright fireball that streaked out of the constellation Perseus, there were dozens more ordinary meteors struggling to be seen through the moonlight. It will be a much different story in 2018: Next year, the Perseids will coincide with a new moon!
In contrast to the Perseids, the moon provided little or no interference with the recent Geminid meteor shower. Based on data from the IMO, the "Gems" peaked within an hour of their forecast time on Dec. 14, attaining an incredible hourly rate of 145 — more than two per minute! The Gems provided the very best meteor display of this year, by far. [The 2017 Geminid Meteor Shower: Amazing Photos by Stargazers]
The planets
Venus was certainly the planet to watch when 2017 opened. This most brilliant of planets dazzled evening skywatchers during January and February, setting nearly four hours after the sun and soaring high into the western sky. It became so intensely brilliant that in dark, rural locations it even cast faint shadows.
Venus dropped back toward the sun during March but appeared as a beautiful slender crescent even in binoculars. For a few days around the beginning of April, it was visible both as an evening and a morning object. Venus then fully transitioned to the morning sky as a magnificent predawn object for almost the balance of this year.
Meanwhile, Saturn, the "Lord of the Rings," spent much of the spring and summer in excellent position to be viewed during convenient evening hours. More importantly, its famous and beautiful ring system turned wide open, tilting about as far toward Earth as possible and affording a spectacular sight for viewers even through small telescopes. The rings were, in fact, at their very best since 2003, at a maximum inclination of 27 degrees on Oct. 17.
Jupiter put on a fine evening show for much of the spring and summer, then arrived in conjunction with the sun in late October. When it returned to visibility in mid-November, Venus was the first to greet Jupiter on the 13th: About 45 minutes before sunrise, low to the east-southeast horizon, the two brightest planets rose side by side, separated by only 0.3 degrees and therefore appearing as a spectacular "double planet." Truly a beautiful sight!
Finally, there was Mars, which went on a "summer sabbatical" from June through September, disappearing completely out of sight in the glare of the sun. But next summer will be much different, as the Red Planet will make its closest approach to Earth in 15 years and will appear as a dazzling fiery-hued light in our southern sky.
Comets
There were no bright and spectacular comets this year, but there were several small ones that tried to call attention to themselves.
On Feb. 11, green-hued comet 45P/Honda-Mrkos-Pajdusakova flew past Earth at a distance of only 7.4 million miles (11.9 million km), making the eighth-closest comet flyby of the Space Age. Unfortunately, the comet was invisible to the naked eye; in fact, even observers with telescopes had trouble seeing it. After losing many of its volatile gases when it flew past the sun in December 2016, the depleted comet was a disappointment and ended up much fainter than forecasters expected. [In Photos: The Snow Moon Lunar Eclipse & Comet 45P Close Encounter]
In late March and early April, attention turned to another greenish comet, 41P/Tuttle-Giacobini-Kresak, which passed between the Big and Little Dippers and was visible all night long. At its closest approach on April Fool's Day, this comet was just 13 million miles (21 million km) from Earth — an easy target for backyard telescopes and nearly visible to the naked eye.
And there was a surprise for comet observers from April 4 through April 5, when something happened to comet PanSTARRS (C/2015 ER61), which was more than 112 million miles (180 million km) from Earth at the time. The comet brightened more than six-fold, from magnitude +8.5 to +6.5, suddenly reaching the verge of naked-eye visibility despite its great distance from our planet.
In mid-June came comet Johnson (C/2015 V2), a dim eighth-magnitude comet which made its closest approach to the sun at 149 million miles (239 million km) on June 16. But this solar encounter set the stage for an infinite departure. Gravitational perturbations placed comet Johnson into a hyperbolic orbit, which means that it will never return to the inner solar system. It has now disappeared, on a course to travel through the depths of space forever.
To sum up: 2017 was an action-packed year, celestially speaking. Let's hope for more of the same in 2018!
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmer's Almanac and other publications, and he is also an on-camera meteorologist for Verizon Fios1 News, based in Rye Brook, NY. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.
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