Starship Asterisk*

JohnD wrote: ↑Sat Oct 20, 2018 9:44 am

Chris Peterson wrote: ↑Tue Oct 15, 2013 11:49 pm

Anthony Barreiro wrote:I've had the impression that because Comet ISON's orbit is hyperbolic, this will be it's one and only pass through the inner solar system. Have I been laboring under a misapprehension?

Yes, you have been somewhat under a misapprehension. In fact, most comets with hyperbolic orbits are actually periodic (although all long period comets which haven't been observed before are called non-periodic). So-called hyperbolic orbit comets typically have eccentricities only very slightly greater than one, and those eccentricities drop below one again once they are some distance from the Sun. The result is a comet with a period of hundreds of thousands or more years (there's no way to reliably determine the period of such comets), but definitely an orbit that will remain closed around the Sun. Only a very few comets have been observed on obvious ejection orbits.

C/2012 S1 is almost certainly periodic.

Revival of this thread, to ask about the difference between "non-periodic" comets, AKA never seen before, comets with very long orbits, and Oumuamua. Chris, you said above that some long orbit comets cannot have their period determined, but that some have been on ejection orbits. That was five years ago.
Oumuamua was unique in that it was clearly rocky, with little or no tail but was announced as definitely coming from outside the Solar System and heading away, never to return. Has orbit calculation improved since then, to allow such confidence? Or could previous icy, tailed comets have been extra-solar?
John

Chris Peterson wrote: ↑Tue Oct 15, 2013 11:49 pm

Anthony Barreiro wrote:I've had the impression that because Comet ISON's orbit is hyperbolic, this will be it's one and only pass through the inner solar system. Have I been laboring under a misapprehension?

Yes, you have been somewhat under a misapprehension. In fact, most comets with hyperbolic orbits are actually periodic (although all long period comets which haven't been observed before are called non-periodic). So-called hyperbolic orbit comets typically have eccentricities only very slightly greater than one, and those eccentricities drop below one again once they are some distance from the Sun. The result is a comet with a period of hundreds of thousands or more years (there's no way to reliably determine the period of such comets), but definitely an orbit that will remain closed around the Sun. Only a very few comets have been observed on obvious ejection orbits.

C/2012 S1 is almost certainly periodic.

Chris Peterson wrote:

Anthony Barreiro wrote:I've had the impression that because Comet ISON's orbit is hyperbolic, this will be it's one and only pass through the inner solar system. Have I been laboring under a misapprehension?

Yes, you have been somewhat under a misapprehension. In fact, most comets with hyperbolic orbits are actually periodic (although all long period comets which haven't been observed before are called non-periodic). So-called hyperbolic orbit comets typically have eccentricities only very slightly greater than one, and those eccentricities drop below one again once they are some distance from the Sun. The result is a comet with a period of hundreds of thousands or more years (there's no way to reliably determine the period of such comets), but definitely an orbit that will remain closed around the Sun. Only a very few comets have been observed on obvious ejection orbits.

C/2012 S1 is almost certainly periodic.

Ann wrote:I'll never forgive myself for missing Comet Hyakutake. The weather was brilliant during those few days when it was at its brightest. For some reason I didn't think I could see it. I didn't even look up to check. And when my neighbour asked me about it, I told him he couldn't see it.

And Hyakutake may have been the bluest comet ever, too. :( :( :( :(

Anthony Barreiro wrote:I've had the impression that because Comet ISON's orbit is hyperbolic, this will be it's one and only pass through the inner solar system. Have I been laboring under a misapprehension?

neufer wrote:

http://en.wikipedia.org/wiki/Comet_ISON wrote:
<<The comet's formal designation is C/2012 S1. The "C" indicates that it is non-periodic, followed by the year of discovery. >>

http://en.wikipedia.org/wiki/Comet_ISON wrote:
The names of famous short-period comets usually identify the astronomers who discovered them or clearly identified them as a periodic comet, such as Halley's Comet or Comet Swift–Tuttle. If that convention had been followed, "Comet ISON" would be referred to instead as Comet Nevski–Novichonok or C/2012 S1 (Nevski–Novichonok).>>

Anthony Barreiro wrote:

APOD Robot wrote:
... Currently, sky enthusiasts await Comet ISON's continued brightening in the coming weeks, unsure how interesting its first journey to the inner Solar System will be.

I've had the impression that because Comet ISON's orbit is hyperbolic, this will be it's one and only pass through the inner solar system.

• Indubitably

http://en.wikipedia.org/wiki/Comet_ISON wrote:
<<The comet's formal designation is C/2012 S1. The "C" indicates that it is non-periodic, followed by the year of discovery. The "S" represents the half-month of discovery—in the case of C/2012 S1, the second half of September—and the number "1" shows that this was the first comet found in that half month.The addition of "(ISON)" after its name merely identifies the organization where its discovery was made, the Russia-based International Scientific Optical Network. If the same organization had discovered a similar, but unrelated comet one day later, that one would have been named "C/2012 S2 (ISON)". Nevertheless, media sources have taken to referring to C/2012 S1 by its location of discovery, and consequently, this name will likely persist in use even though it may cause confusion with later discoveries made by the ISON organization. The names of famous short-period comets usually identify the astronomers who discovered them or clearly identified them as a periodic comet, such as Halley's Comet or Comet Swift–Tuttle. If that convention had been followed, "Comet ISON" would be referred to instead as Comet Nevski–Novichonok or C/2012 S1 (Nevski–Novichonok).>>

APOD Robot wrote:... Currently, sky enthusiasts await Comet ISON's continued brightening in the coming weeks, unsure how interesting its first journey to the inner Solar System will be.

neufer wrote:

Chris Peterson wrote:

BDanielMayfield wrote:
I was impressed by how radically the comet’s orbit had been changed, going from a period of around 4200 years down to only about 2400. This comet really was putting on the breaks, so to speak, to have reduced the period and therefore size of it's orbit by such a large amount. Why did it slow down so much? My quess would be outgassing jets, but is that the only force working to slow this object?

No, outgassing has nothing to do with it. Those forces are very small.
The orbit of Hale-Bopp (and many other comets) is unstable due to gravitational interactions with Jupiter.

• A velocity reduction near Jupiter of ~100 m/s is more than sufficient.

http://en.wikipedia.org/wiki/Comet_Hale%E2%80%93Bopp wrote:

<<Comet Hale–Bopp likely made its last perihelion 4,200 years ago. The comet may have been observed by ancient Egyptians during the reign of pharaoh Pepi I (2332–2283 BC). In Pepi's pyramid in Saqqara is a text referring to an "nhh-star" as a companion of the pharaoh in the heavens, where "nhh" is the hieroglyph for long hair.

Its orbit is almost perpendicular to the plane of the ecliptic, which ensures that close approaches to planets are rare. However, in April 1996 the comet passed within 0.77 AU of Jupiter, close enough for its orbit to be affected by the planet's gravity. The comet's orbit was shortened considerably to a period of roughly 2,533 years, and it will next return to the inner Solar System around the year 4385. Its greatest distance from the Sun (aphelion) will be about 370 AU, reduced from about 525 AU.

Over many orbits, the cumulative effect of gravitational perturbations on comets with high orbital inclinations and small perihelion distances is generally to reduce the perihelion distance to very small values. Hale–Bopp has about a 15% chance of eventually becoming a sungrazing comet through this process.

It has been calculated that the previous visit by Hale–Bopp occurred in July 2215 BC. The comet may have presented a similar sight to people then, as the estimated closest approach to Earth was 1.4 AU, but no records of it have survived. Hale–Bopp may have had a near collision with Jupiter in early June 2215 BC, which probably caused a dramatic change in its orbit, and 2215 BC may have been its first passage through the inner Solar System.

The estimated probability of impacting Earth in future passages through the inner Solar System is remote, about 2.5 x 10−⁹ per orbit. However, given that the comet nucleus is around 60 km in diameter, the consequences of such an impact would be apocalyptic. A calculation given by Weissman conservatively estimates the diameter at 35 km [thereby yielding] about 44 times the estimated energy of the K-T impact event.>>

unhappy memory wrote:
I remember Hale-Bopp for the news it made here in San Diego County. The Nut Cases who partied like there was no tomorrow, downing strange shooter concoctions and leaving bags of trash behind for the people still here to clean up. As I recall, they left the county riding on the tails of Hale-Bopp. Never a word back from them as to how the trip went.

• They're probably too busy taking in Vogon poetry right now.

http://en.wikipedia.org/wiki/Heaven%27s_Gate_%28religious_group%29 wrote:
<<Heaven's Gate was an American UFO religion doomsday cult based in San Diego, California, founded in the early 1970s and led by Marshall Applewhite (1931–1997) and Bonnie Nettles (1927–1985). On March 26, 1997, police discovered the bodies of 39 members of the group who had committed mass suicide in order to reach what they believed was an alien space craft following the Comet Hale–Bopp, which was then at its brightest. Heaven's Gate members believed that the planet Earth was about to be "recycled" (wiped clean, renewed, refurbished and rejuvenated), and that the only chance to survive was to leave it immediately.>>

http://en.wikipedia.org/wiki/The_Hitchhiker%27s_Guide_to_the_Galaxy_%28novel%29 wrote:
<<The Hitchhiker's Guide to the Galaxy by Douglas Adams was first published in London on 12 October 1979. The book begins with contractors arriving at Arthur Dent's house, in order to demolish it to make way for a bypass. His friend, Ford Prefect, tries to explain to Arthur that the Vogons, an alien race, intend to destroy Earth to make way for a hyperspace bypass. The two escape by hitching a lift on one of the Vogon demolition ships. This is, however, against Vogon regulations, and when the pair are discovered, they are tortured with hearing Vogon poetry, the third worst in the known Universe, and then thrown into space.>>

Chris Peterson wrote:I did get some nice images, but I regret deeply that this comet came around just a few years too early for the digital camera revolution. Film is such a limited means of collecting images, especially low-light images. To have a comet like Hale-Bopp again, with today's imaging technology!

Chris Peterson wrote:

neufer wrote:
I saw [Hale Bopp] from the dark skies of Skyline Drive.

My most memorable comet since Comet Mrkos in 1957 from the dark skies of Camp Pocomoonshine on Lake Champlain.

Hale-Bopp was a truly impressive sight, although I think I was less impressed by it than I would have been had I not seen Hyakutake just one year before. Hyakutake made Hale-Bopp look rather insignificant. To have two "comets of the century" so close together says something about statistics...

• Like many others, I wasn't so lucky with the weather.

http://en.wikipedia.org/wiki/Hyakutake wrote:

[b][color=#0000FF]Hyakutake on the evening of its closest approach to Earth on 25 March 1996[/color][/b]

---

<<Comet Hyakutake was dubbed The Great Comet of 1996; its passage near the Earth was one of the closest cometary approaches of the previous 200 years.

Hyakutake became visible to the naked eye in early March 1996. By mid-March, the comet was still fairly unremarkable, shining at 4th magnitude with a tail about 5 degrees long. As it neared its closest approach to Earth, it rapidly became brighter, and its tail grew in length. By March 24, the comet was one of the brightest objects in the night sky, and its tail stretched 35 degrees. The comet had a notably bluish-green colour.

The closest approach occurred on 25 March. Hyakutake was moving so rapidly across the night sky that its movement could be detected against the stars in just a few minutes; it covered the diameter of a full moon (half a degree) every 30 minutes. Observers estimated its magnitude as around 0, and tail lengths of up to 80 degrees were reported. Its coma, now close to the zenith for observers at mid-northern latitudes, appeared approximately 1.5 to 2 degrees across, roughly four times the diameter of the full moon. Even to the naked eye, the comet's head appeared distinctly green, due to strong emissions from diatomic carbon (C₂).

Because Hyakutake was at its brightest for only a few days, it did not have time to permeate the public imagination in the way that Comet Hale–Bopp did the following year. Many European observers in particular did not see the comet at its peak because of unfavourable weather conditions.

The Ulysses spacecraft made an unexpected pass through the tail of the comet on 1 May 1996. Evidence of the encounter was not noticed until 1998. Astronomers analysing old data found that Ulysses' instruments had detected a large drop in the number of protons passing, as well as a change in the direction and strength of the local magnetic field. This implied that the spacecraft had crossed the 'wake' of an object, most likely a comet; the object responsible was not immediately identified.

Based on the Ulysses encounter, the comet's tail is known to have been at least 570 million km (3.8 AU) long. This is almost twice as long as the previous longest-known cometary tail, that of the Great Comet of 1843, which was 2.2 AU long.>>

neufer wrote:I saw it from the dark skies of Skyline Drive.

My most memorable comet since Comet Mrkos in 1957 from the dark skies of Camp Pocomoonshine on Lake Champlain.

Chris Peterson wrote:

BDanielMayfield wrote:
I was impressed by how radically the comet’s orbit had been changed, going from a period of around 4200 years down to only about 2400. This comet really was putting on the breaks, so to speak, to have reduced the period and therefore size of it's orbit by such a large amount. Why did it slow down so much? My quess would be outgassing jets, but is that the only force working to slow this object?

No, outgassing has nothing to do with it. Those forces are very small.
The orbit of Hale-Bopp (and many other comets) is unstable due to gravitational interactions with Jupiter.

• A velocity reduction near Jupiter of ~100 m/s is more than sufficient.

http://en.wikipedia.org/wiki/Comet_Hale%E2%80%93Bopp wrote:

<<Comet Hale–Bopp likely made its last perihelion 4,200 years ago. The comet may have been observed by ancient Egyptians during the reign of pharaoh Pepi I (2332–2283 BC). In Pepi's pyramid in Saqqara is a text referring to an "nhh-star" as a companion of the pharaoh in the heavens, where "nhh" is the hieroglyph for long hair.

Its orbit is almost perpendicular to the plane of the ecliptic, which ensures that close approaches to planets are rare. However, in April 1996 the comet passed within 0.77 AU of Jupiter, close enough for its orbit to be affected by the planet's gravity. The comet's orbit was shortened considerably to a period of roughly 2,533 years, and it will next return to the inner Solar System around the year 4385. Its greatest distance from the Sun (aphelion) will be about 370 AU, reduced from about 525 AU.

Over many orbits, the cumulative effect of gravitational perturbations on comets with high orbital inclinations and small perihelion distances is generally to reduce the perihelion distance to very small values. Hale–Bopp has about a 15% chance of eventually becoming a sungrazing comet through this process.

It has been calculated that the previous visit by Hale–Bopp occurred in July 2215 BC. The comet may have presented a similar sight to people then, as the estimated closest approach to Earth was 1.4 AU, but no records of it have survived. Hale–Bopp may have had a near collision with Jupiter in early June 2215 BC, which probably caused a dramatic change in its orbit, and 2215 BC may have been its first passage through the inner Solar System.

The estimated probability of impacting Earth in future passages through the inner Solar System is remote, about 2.5 x 10−⁹ per orbit. However, given that the comet nucleus is around 60 km in diameter, the consequences of such an impact would be apocalyptic. A calculation given by Weissman conservatively estimates the diameter at 35 km [thereby yielding] about 44 times the estimated energy of the K-T impact event.>>

LocalColor wrote:We both remember Hale-Bopp and how we tried to get good photos of it.

BDanielMayfield wrote:I was impressed by how radically the comet’s orbit had been changed, going from a period of around 4200 years down to only about 2400. This comet really was putting on the breaks, so to speak, to have reduced the period and therefore size of it's orbit by such a large amount. Why did it slow down so much? My quess would be outgassing jets, but is that the only force working to slow this object?

Beyond wrote:

Otto Posterman wrote:Do you remember comet Hale-Bopp?

No. I missed it completely. I've only seen one comet and that one required binoculars. Now that i pay a little more attention to the sky, i find that it's usually cloudy when something occurs. As Walter Cronkite (remember him?) used to say, "That's the way it is", and then he'd add the date. I don't add the date, because where i am, that's almost always "The way it is".

With a well-established orbit, astronomers know the comet probably passed its last perihelion about 4200 years ago, and it will next pass perihelion after another 2380 years.

Otto Posterman wrote:
Do you remember comet Hale-Bopp?

http://en.wikipedia.org/wiki/Comet_Arend%E2%80%93Roland wrote:
<<Carl Sagan relates an anecdote on page 80 of his book Cosmos about being on duty in an observatory near Chicago in 1957 when a late night phone call from an inebriated man asked what was the "fuzzy thing" they were seeing in the sky. Sagan told the man it was a comet (Arend–Roland). The man asked what a comet was, and Sagan answered that it was "a snowball, one mile wide". After a long pause, the man said, quoting Sagan: "Lemme talk to a real 'shtronomer!".>>