If you set an astronomy app<\/a> to \u2018Show all comets\u2019, your screen will fill with so many dots you won\u2019t be able to see the stars!<\/p> Find out what comets and asteroids are in the sky tonight<\/a>. Discover the greatest comets of recent times<\/a>.<\/em><\/strong><\/p> People used to be very afraid of comets.<\/p> They thought comets were harbingers of doom<\/a>, terrifying cosmic visitors that carried terrible disease, caused calamities like floods, earthquakes and plagues and even heralded the deaths of rulers when they appeared in the sky.<\/p> Today we know that comets are huge, dark, dirty, dusty bodies \u2013 a cross between icebergs and snowballs.<\/p> For most of their existence we can\u2019t see them, because most lurk out in the Oort cloud<\/a>, many thousands of times further from the Sun than Earth, and never leave it.<\/p> Occasionally, a comet is nudged out of the Oort cloud to travel in toward the Sun.<\/p> If it comes close enough to thaw out, it can release huge amounts of glowing gas and reflective dust.<\/p> This can brighten the comet to the point it becomes visible through telescopes and sometimes to the naked eye.\u00a0<\/p> Comets orbit the Sun like the planets do, except their orbits are usually much more elliptical than the roughly circular orbits of the planets.<\/p> Some comets take a long time, others only a very short time \u2013 astronomically speaking \u2013 to orbit the Sun.<\/p> Comets that take less than 200 years to orbit the Sun are classified as short-period comets<\/a><\/strong>.\u00a0<\/p> Comet 2P\/Encke has the shortest period (or year), taking just 3.3 Earth years to complete one orbit of the Sun.<\/p> But the most famous short-period comet is Halley\u2019s Comet<\/a>, which takes 76 Earth years to orbit the Sun.<\/p> Unlike most comets traditionally named after their discoverer(s), this was named after the astronomer Edmond Halley.<\/p> In 1705, Halley\u2019s calculations suggested that the comet had appeared in our sky at regular intervals through history and would reappear again in 1758.<\/p> It did, but unfortunately Halley died before then, so never got to see the comet that bears his name.\u00a0<\/p> Other comets take much longer to orbit the Sun and these long-period comets<\/strong> tend to be the brightest and most active.<\/p> This is because they don\u2019t thaw out so often, so they are still relatively fresh each time they come close to the Sun and release more material.\u00a0<\/p> The most famous long-period comet is Hale\u2013Bopp<\/a>, which was a beautiful sight in our sky in 1997.<\/p> Hale\u2013Bopp takes around 2,530 years to go around the Sun. That\u2019s a long time, but other comets take much longer.<\/p> Comet Hyakutake, which appeared in our sky a year before Hale\u2013Bopp, has an orbital period of around 70,000 years, while the great comet of 1976, Comet West, has an orbital period of about 250,000 years.<\/p> So don\u2019t hold your breath waiting to see that one again!<\/p>![\"Diagram](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2024\/09\/long-period-comets-orbits.jpg\")
Comets orbiting the Sun and brightening<\/strong><\/h2>
Short period comets<\/strong><\/h2>
![\"Comet](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2019\/02\/2P_170123_2400-ffda530.jpg\")
Long-period comets<\/strong><\/h2>
![\"Long-period](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2024\/09\/comet-hale-bopp.jpg\")
![\"Comet](\"https:\/\/c02.purpledshub.com\/uploads\/sites\/48\/2024\/09\/GettyImages-1153507849.jpg\")