The Orbital Path of Halley's Comet
Where does Halley's Comet come from?
The Oort Cloud and Kuiper Belt
Credit: Donald Yeomans (JPL)
Comet Halley, like other comets, is thought to be 4.6 billion years old. Unlike the planets, some material couldn't form into planets and was hurled further and further outward by the large planets. This small, icy material eventually found a home in the "outer" solar system in places called the Kuiper Belt and the Oort Cloud.
The Kuiper Belt is a doughnut-shaped area of space 35 to 50 Astronomical Units ("AU") from our Sun. The Oort Cloud stretches from 1,000 and 100,000 AU and is spherical in shape.
Thousands of comets reach their furthest point from the Sun in the Kuiper Belt including the most famous comet of them all - Halley's Comet. Over a thousand objects have been definitively identified in the Kuiper Belt including three dwarf planets - Pluto, Haumea and Makemake. Although the Oort Cloud is beleived to contain billions of comets, not a single object has been observed in the Oort Cloud.
At some point thousands of years ago, a passing star disturbed the orbit of a comet in the Kuiper Belt. This comet was sent hurling into the "inner" solar system, where it eventually became known as Halley's Comet (1P/Halley). Since its entrance Comet Halley has embraced its newfound role, returning once every 75 to 79 years.
Halley's Comet Enters The Inner Solar System
The orbit of Halley's Comet (1P/Halley) compared to the ecliptic
Credit: Osamu Ajiki (AstroArts) modified by Ron Baalke (JPL)
Unlike the vast majority of other comets, Comet Halley has been visible to the naked eye during every orbit, since its first verifiable observation in 240 BCE. Some orbits, of course, are more spectacular than others. The "show" depends on the amount of material shed from the comet's nucleus and the distance between Halley's Comet and Earth.
The comet loses less than .1% of its mass during each orbit, so it puts on a consistent show and will continue to do so for centuries to come.
Comet Halley enters the inner solar system at an 18° angle relative to the ecliptic. The ecliptic is the relatively flat band of space through which all planets travel (see image). Due to occasional close encounters with a planet or a moon, Comet Halley's path can be altered.
Path of Halley’s Comet in 1910
As mentioned, Comet Halley spends the majority of its life in the Kuiper Belt. From Earth's perspective, the comet lies unseen in the direction of Canis Minor near Cancer. Each time, Halley's Comet enters the inner solar system, Earth's position relative to the comet determines when the comet first becomes visible with a telescope and, ultimately, to the naked eye.
Halley's Comet on April 20, 1910
Credit: Stellarium as seen from Sydney, Australia
Let's take a look at Comet Halley's "rediscovery" in 1910.
Halley's Comet's nucleus entered the inner solar system as it had done countless times before. The Sun heated its cold exterior between the orbit of Saturn and Jupiter and it began to shed material from its dark icy core. This shed material, in the form of water, gas and debris, formed the comet's coma and tails. The coma and tails reflected considerably more light than the dark nucleus, finally allowing the comet's to be observed by astronomers using telescopes. Comet Halley had returned from the Kuiper Belt, making its way toward the Sun.
Halley's Comet became visible to the naked eye in November of 1909, where it could be seen over the western horizon after sunset. In December, it traveled through Pisces and into Aquarius. In February, the comet lied in the direction of the setting Sun and "disappeared" in the Sun's brilliance. After several days, Comet Halley rose in the east before dawn. It was now moving away from the Sun.
Finally, on April 20, 1910 Comet Halley reached its closet point to the Sun. It occurred while the comet was in the constellation Corvus (see image).