Kreutz sungrazer-class Comet Lovejoy photographed December 22, 2011, at the European Southern Observatory in Chile. via
In November, Comet ISON is going to pass close enough to the sun that we’ll see it during the day without binoculars. It’s not unheard of to see a comet during the day, but it is extremely rare. Which means that if NASA’s estimates are correct (and I’m not inclined to distrust the agency on these things) we’re in for a real treat at the end of the year. NASA is holding a teleconference on Friday, February 8, to discuss the latest details on ISON, so for now here’s a look at the only nine comets that have been visible during daylight hours in the last 332 years.
First, a little bit about comets and brightness. The nucleus or core of a comet is typically made of ice or rocky ice coated with dust and organic material. As a comet gets closer to the sun, the ice melts and turns into gas forming a cloud around the nuclear called a coma. Solar radiation pushes dust particles away from the coma forming the familiar tail while charged solar particle ionize the tail. The tail is measured in miles (or feet if it’s small) or degrees – the whole globe of the sky is divided into 360 degrees, 180 degrees from horizon to horizon.
The coma and tail either reflect sunlight or glow by absorbing solar energy. The resulting brightness is expressed as magnitude with larger numbers representing dimmer objects. On this scale, the brightest stars are zero to first magnitude. Brighter objects have negative magnitudes while dimmer objects have positive magnitudes.
1680 – On November 14, 1680, German astronomer Gottfried Kirsch became the first man in history to discover a comet by telescope. Less than a month later, it was dim but visible with a 15 foot long tail by the naked eye. On December 18, observers in Albany, New York reported it as visible at midday as it passed just 744,000 miles from the Sun. Then it started to fade, its tail stretching to about 70 degrees as it melted, before disappearing from the daytime sky in early February 1681.
This one’s an interesting case; it’s orbit is strikingly similar to ISON’s. There’s some speculation that the two comets are either the same or from a similar place in space, but that’s pending confirmation
1744 – A dim comet was spotted on November 29, 1743, by Philippe Loys de Cheseaux of Lausanne, Switzerland. It got steadily brighter as it approached the Sun. By mid-January, it had a 7 degree long tail. By February 1, it was about as bright as Sirius (the brightest star in our sky in the constellation Canis Major) with a curved tail 15 degrees long. By February 18 it had gained a second tail and was giving Venus a run for its money as brightest celestial object. It peaked on February 27 as a -7 magnitude object clearly visible in the daytime. It’s closest point to the Sun came on March 1, and on March 6 it was seen in the morning sky with six tails spread out behind it like a fan.
The Great Comet of 1843 as seen by Mary Morton Allport in Australia. via
1843 – There’s a group of comets called the Kruetz Sungrazing Comet Group that have spawned some of the brightest objects in the sky. These comets orbit the sun such that they actually graze through its outer atmosphere, often getting too close to survive. One of these comets passed only 126,000 miles from the Sun’s surface on February 27, 1843, and was clearly visible in the daytime. It reportedly looked like an elongated white cloud with a short tail about 1 degree in length. As is moved away from the sun, the comet got dimmer but the tail lengthened eventually stretching to 200 million miles.
1882 – Another comet from the Kreutz Sungrazing Group, this one might be the brightest object ever seen. First spotted as a zero-magnitude body on September 1, it continued to brighten as it approached the Sun. By September 14, it was visible in daylight; it reached its brightest on the 17th when it passed just 264,000 miles from the sun's surface. The nucleus broke apart but the pieces stayed together, glowing in the morning sky as an immense object with a bright, long tail.
1910 — Workmen spotted this first magnitude object in the sky over South Africa on January 13, 1910. It was seen again, just before sunrise, two days later. On January 17, it was spotted above the Sun at sunrise and again, finally, at midday as a snow white object brighter than Venus. Over the next few days it dimmed as it moved further from the sun but it was still visible at night. A lot of people who saw this January comet thought it was Halle’s comet, but it wasn’t; that famous ball of ice wouldn’t make it’s predicted appearance for another three months.
1927 — Comet Skjellerup-Maristanny was first seen as a third magnitude object in early December of 1927. It started out dim but got steadily brighter as it approached the Sun, reaching its closest point on December 18. Passing 16.7 million miles from the surface, it was visible during the day as a -6 magnitude object. Then it faded quickly, it’s tail persisting and stretching to 40 degrees by the end of the month before it faded entirely from view.
1965 – Comet Ikeya-Seki, another Kreutz Sungrazer, was visible in the daytime on October 21, 1965, when it passed within 744,000 miles of the center of the sun. That’s really close, making it the undisputed champion of bright objects seen in the 20th century. Observers in Japan described it as being ten times brighter than the full moon; it had a magnitude of about -15 on the brightness scale. Like the January comet of 1910, the nucleus broke into pieces making it easier to see with the naked eye. But it faded pretty quickly, its 75 million mile tail visible through November.
Comet Ikeya-Seki appeared in the dawn sky in 1965. via
1976 – Discovered in photographs taken at the European Southern Observatory in Chile, by Danish astronomer Richard West in November, 1975, Comet West appeared in the morning sky in March of 1976. But the first daytime glimpses came days earlier on February 25. Seventeen hours after it passed 18.3 million miles from the Sun, Comet West was visible about ten minutes before sunset.
2007 – Comet McNaught, was discovered in August 2006 by astronomer Robert McNaught at Australia's Siding Spring Observatory. As it passed the Sun at a distance of just 15.9 million miles on January 12, 2007, it glowed. Brightly. Observers worldwide reported that the comet reached its peak brightness, magnitude 5.1, on Sunday, January 14 at around 7:00 a.m. EST (noon GMT). They also said Comet McNaught developed a fan-like tail, reminiscent of the 1744 comet.
It’s likely we’ll add another daytime sighting to the list in November. And given how infrequently this happens, it’s worth trying to catch a glimpse of ISON if you can.