Should we complain? Two Great Comets have garnished Southern Hemisphere skies within the past 8 years Comet McNaught in 2007 and Comet Lovejoy in 2011 while a generation of northerners have had just photos. We are now treated to a near constant barrage of magnificent comet photos, but be aware that most are from highly experienced amateur astrophotographers using telescopes and solid-state sensors, or from professional astronomers using big telescopes, or even from the International Space Station, above Earths obscuring atmosphere. Meanwhile, from the ground and with the eye alone? Not since Comet Hale-Bopp in 1996-97 has the Northern Hemisphere seen a magnificent comet. Whats more, some skygazers would not classify Hale-Bopp as a Great Comet. In that case, we northerners have to look back to Comet West in 1976 nearly 40 years ago to find a Great Comet.

Lets consider some of the incredible comets of recent times and historic records, to find out when the Northern and Southern Hemispheres might expect to see the next Great Comet.

A night under the stars and Comet Hale-Bopp. It remained visible to the unaided eye for 18 months. Photo 1997 Jerry Lodriguss / http://www.astropix.com. Used with permission.

First, how are we defining a Great Comet? Theres no official definition. The label Great Comet stems from some combination of the comets brightness, longevity and breadth across the sky.

For purposes of this article, to consider the question of Great Comets of the north and south and their frequency, well define Great Comets as those that achieve a brightness equal to the brightest planet Venus (magnitude -3 to -4) or brighter with tails that span 30 degrees or more of the sky.

We can consider some other major comets, too, those that reached magnitude 1 or brighter in other words, they became as bright as the brightest stars with tails spanning 15 degrees or more. These major comets would have been visible long enough for Earths citizenry to take notice (some impressive comets have such extreme orbits that they arent visible long, and hardly anyone besides astronomers notices them).

Halleys Comet in 1986 seconds before closest approach by the ESA spacecraft Giotto. The inset shows comets as depicted in popular illustration duration the time of Halleys 1910 apparition. Big difference! Photo via Giotto/ESA.

Consider, also, how humanitys ability to view the heavens has completely changed in the last 50 years.

In that time, space travel has become a reality and solid-state electronics have revolutionized photography. Space probes have been sent to comets beginning with the European Space Agency (ESA) Giotto spacecraft sweeping past Halleys Comet in 1986, and, most recently, ESAs Rosetta spacecraft which is currently spending many months orbiting and becoming intimately acquainted with 67P/ChuryumovGerasimenko.

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When is our next Great Comet?