Starting on Friday, December 8, we can finally confirm with certainty that Halley’s Comet is coming.
This most famous comet orbits the Sun in a flat, elliptical orbit that brings it close to the Sun and then takes it far beyond the outer limits of the Solar System. Since February 9, 1986, when it reached perihelion – the comet’s closest approach to the sun – it has begun its long journey back into deep space. From that time until the present, the comet has been moving relentlessly away from the Sun.
But at 8pm ET on Friday, December 8 (0100 GMT on December 9) that will end. Because at that moment, Halley’s Comet will reach apogee; The far end of its orbit – that location in space that places the comet furthest from the Sun: 3.27 billion miles (5.26 billion km). The comet will then be 472.2 million miles (759.8 million km) from the orbit of Neptune, the farthest known planet.
The last time Halley reached this point in its orbit was in April 1948.
Related: The Eta Aquarid meteor shower is the legacy of Halley’s Comet in the May night sky
When Halley reaches apogee, its orbital speed will have slowed to just 0.565 miles (0.909 km) per second; About 2,034 miles (3,272 km) per hour. Compare that to the time when the comet was orbiting the Sun at perihelion on February 9, 1986, at 33.77 miles (54.52 km) per second; About 121,572 miles (195,609 km) per hour.
So, after December 8, the comet will again – for the first time in nearly 38 years – approach the Sun. In agreement with Kepler’s second law of motion, a celestial body moves fastest when it is at perihelion and slower at apogee. So, once Halley passes through aphelion, its orbital speed will begin to increase — very slowly at first — on its way inward toward the Sun.
In the table below, we note the times at which Halley will cross the orbits of seven planets as it moves inward toward the Sun. The average distance for each orbit is given in astronomical units (AU). One astronomical unit is equivalent to the Earth’s average distance from the Sun, which is 92,955,807 miles (149,597,870 km).
| Planet orbit | Distance (Australia) | Transit date |
|---|---|---|
| Neptune | 30.6 | May 7, 2041 |
| Uranus | 19.2 | May 1, 2053 |
| Saturn | 9.54 | December 7, 2058 |
| Jupiter | 5.2 | June 25, 2060 |
| Mars | 1.52 | May 16, 2061 |
| Land | 1.0 | June 19, 2061 |
| Venus | 0.72 | July 9, 2061 |
Halley’s Comet will reach perihelion again on July 28, 2061.
We look forward to 2061
So, what can we expect from Halle’s next appearance 38 years from now? With the current average life expectancy for Americans nearing 79, if you were born after 1982, you have a better 50-50 chance of seeing Halley’s return in the summer of 2061.
On its way toward the sun, during late spring and early summer, it will be visible in the morning sky and favors viewers in the Northern Hemisphere.
Interestingly, 2061 is a mirror image of the comet’s last appearance in the winter/early spring of 1986. At that time, the comet was out of sight and on the opposite side of the sun in midwinter; But in mid-summer of 2061, the comet will be on the same side of the sun as us, and will appear fully visible, appearing at least ten times brighter! It will then descend rapidly, and as it enters the evening sky, it will gradually favor southern locations.
But for viewers at mid-northern latitudes, the comet should develop into a striking, albeit low, sight in the western and northwestern sky on early August evenings.
A two-month pageant
The main display in the morning sky begins in mid-June. On June 18, Halley’s Comet will be positioned in the constellation Taurus, 1.2 degrees northwest of the Pleiades. It will be fairly faint at around +5.6 and well-placed observers are unlikely to see its bluish ion tail much longer than 1 degree; An artifact that is 167 million miles (269 million kilometers) away from Earth.
But the comet will approach the Sun and Earth with increasing speed, so with each passing morning, it will appear to climb higher in a darker sky, becoming noticeably brighter.
By July 1, it brightened at magnitude +4.3 with a short tail perhaps two magnitudes long. By July 10, it will be 93 million miles (150 million km) from Earth, and its brightness will double to +3.5. After a week, with its strength now hovering around 2.5 degrees, the tail should appear more pronounced as it reaches about 5 degrees; Halley will race east-northeast across the pentagram of the constellation Auriga.
On July 23, the comet’s head may now be as bright as 1st magnitude, low in the northeastern dawn sky, with a short tail pointing almost upwards from the horizon.
By now, Halley will gradually move from the morning sky to the evening sky, and because it will appear to track about 21 degrees north of the Sun at perihelion, from July 25 to July 28, it will be visible against the late twilight sky. As a zero-volume body in the morning and evening. Now its brilliant white dusty tail that so impressed our ancestors begins to appear.
Evening show… Haley at his best!
At the beginning of August, the comet becomes an exclusively evening object. At first, its view will be obstructed by the presence of a full moon on August 1, but by the evening of August 4, the comet will finally shine in all its glory in a dark sky, low in the west as darkness sets in. .
In fact, August 4-8 may be the peak of 2061’s apparition: the comet’s head brightens as much as 1st magnitude, now accompanied by a straight, narrow tail that streams outward at an angle of 10 or 15 degrees.
In the following evenings, as Halley recedes from the Sun and Earth, its brightness will diminish. Also, as it tracks southeast through the stars of Virgo, it will dip to the horizon: magnitude +1.8 on December 10, and then a reward awaits skywatchers on the evening of December 18, when it forms an isosceles triangle with the crescent moon and Venus approximately four days old. ; It has now diminished to a magnitude of +2.8. Halley then passes within 1 degree of Venus on December 24, having by then faded to 3.3 degrees.
Light pollution is the wild card
With the current average life expectancy for Americans nearing 79, if you were born after 1982, you have a better 50-50 chance of seeing Halley’s return in the summer of 2061.
However, I am very hopeful that over the next 38 years, we will somehow be able to find a solution to dramatically stem the rising tide of light pollution.
If not, there is a very real risk that we will be “bulldozed” and the view of Halley will be obliterated by bright lights. As such, our children and grandchildren may end up being deprived of their legitimate opportunity to say hello to Halle themselves.
In short: Although we can give a pretty good assessment of what Halley’s Comet will do on its next scheduled visit, predicting the state of our night sky by then is a bit of a guess.
Joe Rao is an instructor and guest lecturer at New York University Hayden Planetarium. He writes about astronomy for Natural History Journalthe Farmers Almanac And other publications.
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