Comet Definition and 154 Threads

A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° (60 Moons) across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.
Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star. Long-period comets are set in motion towards the Sun from the Oort cloud by gravitational perturbations caused by passing stars and the galactic tide. Hyperbolic comets may pass once through the inner Solar System before being flung to interstellar space. The appearance of a comet is called an apparition.
Comets are distinguished from asteroids by the presence of an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma (the central part immediately surrounding the nucleus) and the tail (a typically linear section consisting of dust or gas blown out from the coma by the Sun's light pressure or outstreaming solar wind plasma). However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids. Asteroids are thought to have a different origin from comets, having formed inside the orbit of Jupiter rather than in the outer Solar System. The discovery of main-belt comets and active centaur minor planets has blurred the distinction between asteroids and comets. In the early 21st century, the discovery of some minor bodies with long-period comet orbits, but characteristics of inner solar system asteroids, were called Manx comets. They are still classified as comets, such as C/2014 S3 (PANSTARRS). 27 Manx comets were found from 2013 to 2017.As of April 2021 there are 4595 known comets, a number that is steadily increasing as more are discovered. However, this represents only a tiny fraction of the total potential comet population, as the reservoir of comet-like bodies in the outer Solar System (in the Oort cloud) is estimated to be one trillion. Roughly one comet per year is visible to the naked eye, though many of those are faint and unspectacular. Particularly bright examples are called "great comets". Comets have been visited by unmanned probes such as the European Space Agency's Rosetta, which became the first to land a robotic spacecraft on a comet, and NASA's Deep Impact, which blasted a crater on Comet Tempel 1 to study its interior.

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  1. D

    Comet SL9 colliding with Jupiter

    Just curious how this impact would have happened ? Since Jupiter has no core & is all dense gas. Would the pressure have slowed it down until it just exploded? How did the impacts seen from telescope get so big? Was it the extreme winds blowing everything around? Or was it due to a lot more...
  2. T

    Is Earth in Danger from the Incoming Comet?

    Homework Statement A comet is observed in a distance of 100 Earth -radius away from the Earth. It is approaching with a speed of 15000 km/h in a direction only 50 off the line connection the two objects. Earth mass 5.97*1024 kg Earth radius 6.378*106 m Gravity constant 6.6726*10-11 Nm2/kg2 (The...
  3. B

    Calculating Min Δv for a Comet to Intersect Earth's Orbit

    Homework Statement A comet in a circular orbit around the Sun has speed v0 and radius r0 = aRE , where RE is the radius of the Earth’s orbit and α is a constant > 1. The comet has its velocity reduced by Δv in a collision that does not change its initial direction. Show that the...
  4. Q

    Mass/escape velocity of a comet

    Homework Statement On July 4, 2005, the NASA spacecraft Deep Impact fired a projectile onto the surface of Comet Tempel 1. This comet is about 9.0 km across. Observations of surface debris released by the impact showed that dust with a speed as low as 1.0 m/s was able to escape the comet...
  5. G

    Angular Momentum of a Comet Around the Sun

    Homework Statement (a) A certain comet of mass m at its closest approach to the Sun is observed to be at a distance r1 from the center of the Sun, moving with speed v1. At a later time the comet is observed to be at a distance r2 from the center of the Sun, and the angle between rvec2 and the...
  6. S

    Query - could a comet impact create a wormhole?

    probably a dumb question but could a comet or asteroid impact ever create a mini wormhole or mini black hole or the like? also what's worse in terms of impact damage? - a comet, asteroid or meteor? thanks
  7. M

    How Long Does It Take a Comet to Travel 80 Degrees Around the Sun?

    Homework Statement A comet passes the sun at a distance of closest approach R = 6 * 10^8 m and speed 8 * 10^5 m/sec. How long will it take to travel 80 degrees around its orbit from the point of closest approach. Homework Equations omega = velocity / radius The Attempt at a...
  8. S

    Speed update of a comet in an ELLIPTICAL orbit

    A comet is in an elliptical orbit around the Sun. Its closest approach to the Sun is a distance of 5e10 m (inside the orbit of Mercury), at which point its speed is 9e4 m/s. Its farthest distance from the Sun is far beyond the orbit of Pluto. What is its speed when it is 6e12 m from the Sun...
  9. O

    Speed of a comet around the sun.

    Homework Statement A comet is in an elliptical orbit around the Sun. Its closest approach to the Sun is a distance of 4.5e10 m (inside the orbit of Mercury), at which point its speed is 9.6e4 m/s. Its farthest distance from the Sun is far beyond the orbit of Pluto. What is its speed when it...
  10. F

    Huge comet seen on soho web page.

    This new comet is a sun grazer, remember comet neat in 2003? It was is almost 2 times the size of jupiter.. This one may be bigger, but there is no comet tail, why? More about this when it gets closer to the sun, 2 or 3 days?
  11. Q

    How Do You Calculate the Final Speed of a Comet in Orbit?

    Homework Statement (a) A certain comet of mass m at its closest approach to the Sun is observed to be at a distance r1 from the center of the Sun, moving with speed v1. At a later time the comet is observed to be at a distance r2 from the center of the Sun, and the angle between rvec2 and...
  12. C

    Calculating Halley's Comet Orbit Eccentricity & Semi-Major Axis

    Homework Statement Consider Comet Halley. At a particular instant in time, its position and velocity are given below, in units of AU and AU/yr relative to the centre of the Sun. (x,y,z) = 0.331060, -0.455488, 0.166180) (vx,vy,vz) = (-9.01154, -7.02645, -1.30645) There are a number...
  13. J

    Comet with eccentricity of 0.7 and 200 year period

    Homework Statement A comet of the star Sol has an eccentricity of .7. It takes 200 yrs to complete on orbit 1)find the average distance of the comet from Sol. 2) Find the perihelion and aphelion distances from Sol 3)find the velocity of the comet at perihelion Homework Equations...
  14. A

    Comet C/2008 O2 McNaught photos?

    Comet C/2008 O2 McNaught photos?? Hey guys, I was wondering why there aren't any photos of this comet around. It's quite bright (7.2 mag) and its position is very favorable towards the observers on the northern hemisphere- near the pole, actually... Usually, there would be some galleries on...
  15. O

    What is the Equation for Calculating Halley's Comet Eccentricity?

    Homework Statement I am given Rp=.6AU and need to find the eccentricity. Homework Equations Rp=a(1-e) The Attempt at a Solution I can find what Halley's comet eccentricity is (0.967) but I need to actually calculate it. What is the equation I need? I know I need to know Ra, or a...
  16. D

    Comet Orbit Astrophyiscs question

    Homework Statement "Supposing that at perihelion a comet is 1 Au from the sun and its speed at that point is 200km/s( in a frame of referance in which sun is stationary). Find its mean PE and KE to one sig digit. Does it satisfy the virial theorem? Homework Equations K= .5mv^2 U=-GMm/r...
  17. R

    If a comet kicks the moon out of its orbit and away from earth

    If a comet kicks the moon, or any celestial object for that matter, out of its orbit and away from the earth, would it alter Earth's rotational axis?
  18. Maroc

    Make a Comet Look-Alike - Step-by-Step Guide

    Yes you read right do you want to make a Comet look alike ? This is what you will need: - Water - Soy Sauce - Grind up Rocks - Dry Ice - Bag - Bowl - Regular Ice Directions Get a bag and place it opened into a bowl. add water say around 500 ml, then add ice, grind rocks, and...
  19. M

    Comet Tails: A Mystery of Solar Forces

    Did you know... ...that a comet's tail doesn't indicate the direction in which the comet is flying? I didn't, but having come across "Deep Impact" on TV yesterday made me wonder how a comet could have a tail formed from its coma when there is no friction to extend the dust to such a tail. And...
  20. R

    What makes an asteroid an asteroid and not a comet

    Hi all Have been thinking about this for sometime, what is the fundamental difference that makes an asteroid an object orbitting around the star at a lesser speed and not a comet? Hope my question is clear, framing it otherwise why do asteroids not turn into raging comets or comets into...
  21. E

    Why is the dust tail of a comet a tail?

    is it also due to solar wind? if so why is it in a different direction than the gaz tail?
  22. S

    The Next Naked Eye Comet: What to Expect & When

    When will the next comet apear for Earth viewers. I know that there is almost always a comet or two visable through a large telescope but when is the next one visable with the naked eye(I want to plan somthing import on that night.) . I wish i was around for comet Hale-Bopp but i was to young.
  23. sas3

    Stargazing Surefire Tips for Photographing Comet Lulin?

    Can someone take some pictures of Comet Lulin, I will not be able to make it up-North in time ( that’s where my telescope and camera are). I have been reading about it and see it has an anti tail. I never even heard of an anti tail, In some of the pictures I have seen on-line it seems to have...
  24. S

    Calculating Speed of Halley's Comet at Aphelion/Perihelion

    I am trying to figure out the speed of Halley's Comet in km/sec. at aphelion and perihelion... my answers just don't seem to be practical.. please help thanks... I am using v² = (4Π²a³) / (P²) * ((2/r) - (1/a)) where a = mean distance from the sun (semimajor axis of the ellipse) P=...
  25. C

    Orbit of Comet 17P Holmes - equations

    Im trying to learn how to calculate orbits. Comet 17P Holmes e: 0.432668 q: 2.053207 Ascending Node: 326.8586 w: 24.2856 Inclination: 19.1134 Epoch: 2454600.5 (2000) Tp: 20070504.5695 I can calculate Semi Major Axis, Semi Minor Axis, semi-latus rectum, Period in years a =...
  26. S

    Solving Kepler's Equation for Comet Orbit Time Around Sun

    Homework Statement A comet is 10 times farther from the sun than the Earth. Find the time it take to make its orbit around the sun. Homework Equations T^2/R^3 = K K= 3.36X10^18 The Attempt at a Solution I tried to create a ratio, but I honestly have no idea where to start...
  27. J

    Calculating the mass of a comet using the impact method

    [SOLVED] Mass of a comet problem On July 4, 2005, the NASA spacecraft Deep Impact fired a projectile onto the surface of Comet Tempel 1. This comet is about 9.0 {\rm km} across. Observations of surface debris released by the impact showed that dust with a speed as low as 1.0 {\rm m/s} was...
  28. S

    How close will comet come to earth

    I'm given the six orbital parameters for a comet and am asked to find how close it comes to earth, but I'm not sure how to go about this... Should I calculate the position of the comet and Earth and the comet's perihelion passage? If so, are there equations for this type of thing? The...
  29. C

    3 explanations of comet velocity. OK?

    [SOLVED] 3 explanations of comet velocity. OK? Homework Statement This is from Advanced Physics by Adams and Allday, spread 3.31. Explain why comets in very eccentric orbits move very slowly far from the Sun and very fast close to it. Give three explanations, one in terms of energy, one...
  30. K

    What is the speed of the comet when it crosses the Earth's orbit?

    Homework Statement There is a system of 3 bodies, consisting of the sun, the Earth and a comet. When the comet is at perihelion it is at a distance half that of the Earth's orbital radius. At this point it has a speed twice that of the earth's. Ignore the gravitational forces between the...
  31. K

    Position vector relation between comet and earth

    Homework Statement There is a comet that is at a position between the Earth and the sun that has an orbital radius half that of Earth's, this is the perihelion position for the comet. The comet's and Earth's orbits are coplanar. The comet's orbit crosses that of the earth's. When the comet...
  32. DaveC426913

    Is the sky map for Comet Holmes accurate?

    I went out and spotted Holmes tonight. Nice little blob next to Mirfak. Tomorrow I'll get out my scope. I want to see its track so I'm looking for a sky map that shows its path. http://en.wikipedia.org/wiki/Image:Comet_Holmes_trajectory_TLR1.gif" but there's something weird about the map...
  33. W

    What is the Naked Eye Comet in Perseus?

    Hey guys. If it is clear out in your part of the World, look to the left of Delta and Alpha Perseus. There is a naked eye comet there. Look for a fuzz ball (it doesn't have a tail) that makes a point in a equallateral triangle with delta and alpha. It is beautiful in a telescope.
  34. J

    Comet Orbit Around the Sun: Calculating Speed

    A comet is in an elliptical orbit around the Sun. Its closest approach to the Sun is a distance of 4.5 1010 m (inside the orbit of Mercury), at which point its speed is 8.9 104 m/s. Its farthest distance from the Sun is far beyond the orbit of Pluto. What is its speed when it is 6 1012 m from...
  35. E

    Troubleshooting Kepler's Third Law with Halley's Comet

    Homework Statement When I plug in all of the parameters for Halley's comet (from Wikipedia) into Kepler's third law a get a semimajor axis of 38.56 AU when it should be about 17? Can someone else try it and see if I am crazy?Homework Equations The Attempt at a Solution
  36. Saladsamurai

    Can You Hunt for Comets? Understanding the Art of Comet Hunting

    Question About "Comet Hunting" So I I was glancing at the Google sky site when I happened upon a little clip about the Messier catalog. It was interesting to see that that was how it got its name, from a man whom was "comet hunting" and happened to catalog these other celestial wonders. (I am...
  37. K

    Request: comet projectory calculating tool

    Hi (I hope I'm posting in the right place) In physics class we are currently working with projectories of comets etc. that reach the orbit of planets, and get pulled in by its gravity. My teacher is currently doing the work in an excel document, but has requested a better solution for...
  38. P

    Comet Decay: Understanding the Forces Impacting It

    I know that a comet often has a nuclea and a very long tail. the gravitation force of the core on the tail particles must be very weak and they will not have opportunity to come back to the core. So consequently, the comet will decay over time won't it? Is that right?
  39. N

    Why is a Comet More Dangerous Than an Asteroid?

    There's all sorts of speculations about Earth's distruction. Some say it's going to end as the words in the Bible and Mayan calendar say in 2012. No without majic the only way this cn occer is Science. An asteroid aside from a super volcano i s the only thing I know that could bring about...
  40. DaveC426913

    How is a Comet Defined?

    This seems a rather ignorant thing to say: http://www.physorg.com/news91889915.html They're talking about originally defining Pluto as a planet, but see bold: "...At the time, there was a debate about what to call this thing. There weren't that many options. Can you call it an asteroid...
  41. P

    Birght comets like Comet McNaught

    Some comets like Comet McNaught glow very brightly in the sky. However, they are not a sun, obviously. They are just large chunks of rock? It can't just be from the sun's reflection? Or is it as the bright ones have an ice coating around them. I know they have large kinetic energy but not enough...
  42. russ_watters

    Comet McNaught: The Brightest in History?

    ...and we in the northern hemisphere won't see it at its best. Comet McNaught is predicted to reach between mag -4 and -9. At -4 (I think it is already there), it is merely the brightest in 30 years. At -9, it could be the brightest ever recorded. People are taking pictures of it with...
  43. L

    Compute Aphelion from Eccentricity & Perihelion

    If I have the eccentricity and the perihelion of an orbit given, how can I compute the aphelion?
  44. George Jones

    Exploring the Night Sky: Observing the Current Comet

    I saw the comet earlier tonight using 15x70 binoculars in the middle of a small city. It's a brighter than (and not too far from) M13, and should be a fairly easy naked eye object in semi-dark skies. Anyone had any good views?
  45. Orion1

    Is This a Video of a Small Asteroid or Comet Impacting Earth's Atmosphere?

    Is this a video of a small asteroid or comet impacting Earth's atmosphere? Exactly what kind of scientific data is being displayed in this video? Reference: http://video.google.com/videoplay?docid=-9105627519592040246
  46. M

    Comet Impact on Earth May 25th - Is It True?

    Hey everyone, I am not sure if this is the right place to post, but here, it says that a commet will hit Earth on my 25th (in 4 days), and exactly, the atlantic ocean. That means, it will cause a mega tsunami... Everyone is talking about that here in Morocco (since "we are the first ones to be...
  47. P

    So, what would happen if a comet the size of our moon collided with Venus?

    Hello what if a big comet(let's say, as big as our moon), made mainly of ice(95%), hit venus, 1) Would this change the orbit of venus, and if it did, would there be any effects on Earth and any other planets. 2) Would the atmosphere of venus changed, if yes, what would be the...
  48. Z

    Aphelion/Perihelion of Halleys comet

    Q.Halley's comet is in an elliptic orbit about the sun. The orbit eccentricity is 0.967 and the period is 76 years. Taking the mass of the sun to be 2 \times 10^30 kg abd the usual value of G, determine the max and min distances of the comet from the sun. Now I've worked out teh answers but...
  49. Moonbear

    NASA Astrologist sues NASA over comet crash

    http://reuters.excite.com//article/20050705/2005-07-05T134242Z_01_L04309275_RTRIDST_0_ODD-RUSSIA-HOROSCOPE-DC.html :rolleyes: :smile: I feel bad for whoever the people are at NASA who have to actually deal with the legal nonsense, but I sure do wish I was there to see the expression on the...
  50. U

    Calculating Speed of Comet at Greatest Distance from Sun

    A comet moves in an elliptical orbit around the sun. It's closest approach to the sun is 0.59 AU and its greatest distance form the sun is 35AU. If the comet's speed at its closest approach is 54 km/s what is the speed when it is farthest away? Angular momentum is conserved and the gravitational...
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