Have not had a really clear day in about 4 days now.. anyone caught a glimpse yet?
some facts about it...
from..
http://www.slate.com/blogs/bad_astronomy/2013/11/21/comet_ison_12_cool_facts.html
1) ISON is a n00b.
Some comets are on long, elliptical orbits dropping them in to the inner solar system before sailing them back out to the depths of space. There, they slow, stop, then fall once again back into the warmth and light. Comet Halley, for example, is on a 75-year orbit that takes it out past Neptune.
But some are more extreme. If they get an extra kick on their way in perhaps from a collision, or a boost by a planets gravity their elliptical orbit gets turned into an open-ended hyperbola: they have more than enough energy to leave the solar system forever. Once theyre gone, theyre gone.
ISON is a hyperbolic comet, which means this is it: These next few weeks are our only chance to see it. After it swings back out, it aint coming back. This is likely its first tour of the inner solar system as well, which is why scientists are so excited about it; were seeing a pristine comet, billions of years old, a relic of the ancient solar system. Its a time capsule, letting us study what conditions were like when the Sun and planets were young.
2) ISON is a sun-diver.
The orbit of ISON passes very close to the Sun. This diagram shows what NASA/ESA's SOHO satellite will see; the various circles are the different fields of view of SOHO's cameras. Photo by NASA / ESA / SOHO
The orbit of ISON takes it very, very close to the Suns surface. Next week, on Nov. 28, it will skim a mere 1.1 million kilometers (about 700,000 miles) above the Suns surface. Given that the Sun is 1.4 million km across, thats a mighty close shave! The heat it feels will be intense, and it may not survive the encounter (see #10 below).
3) When it passes the Sun, it will be moving at 360 kilometers per second.
Imagine dropping a rock. The higher you drop it, the longer the Earths gravity has to pull on it, and the faster itll be moving when it hits the ground.
The fastest a rock can hit the Earth is if you drop it from infinitely far away. When it hits itll be moving at escape velocity and the physics of dropping it is reversible, so if you throw a rock at escape velocity it will continue on forever (hence the term "escape velocity").
Comet SWAN (left) on a death dive into the Sun in 2012. Photo by NASA / ESA / SOHO
The same is true for a comet rounding (or, in some cases, impacting) the Sun. Since ISON is falling from essentially infinitely far away, when it goes around the Sun itll be moving at the Suns escape velocity at that distance, or just about 360 km/sec (225 miles/sec). How fast is that? Well, it's hundreds of times faster than rifle bullet, for example, and over 1500 times faster than a commercial jet at that speed, the comet would cross the continental United States in about 15 seconds.
In fact, it will be moving at 0.1% the speed of light! Thats far faster than any human-made space probe has ever traveled. And the only propulsion it uses is gravity.
[CORRECTION (Nov. 22, 2013 at 16:15 UTC): I made an error in the calculation for this section, using the escape velocity for the Sun's surface, and not for the distance ISON will be from the Sun's center. This deserves a longer explanation, so I wrote a follow-up post about it, and simply corrected the problem here.]
4) The solid part of ISON is only about two kilometers across.
The nucleus of comet Hartley 2, seen up close during a flyby of the EPOXI spacecraft in 2010. You can see jets of material (ice turning into gas) from pockets on the surface. Photo by NASA / JPL-Caltech / UMD
Comets are actually lumps of rock, gravel, and ice mixed together. This solid part of the comet is called the nucleus, and some are huge; Hale-Bopp had a nucleus about 30 km (20 miles) across.
ISON, though, is tiny, only about 2 km (1.2 miles) across. Heck, plop it down in the middle of the Rocky Mountains and youd hardly notice it! The size has been estimated using images taken from the Hubble Space Telescope, which in reality only give us an upper limit. It might even be smaller.
Still, thats enough to make the comet visible to the naked eye even from a distance of a hundred million kilometers! How can that be? Why, its because
5) The coma is well over 100,000 km in size.
A very rough comparison of the physical size of ISONs coma and the Earth. On this scale, the solid nucleus of ISON would be about the size of a bacterium. Comet photo by Damian Peach
When you look at a picture of ISON (or any comet), youre not seeing the nucleus. Youre seeing the gas surrounding it that was once frozen beneath the surface. When the comet gets near the Sun this ice warms and turns directly into a gas. It escapes the weak gravity of the nucleus, forming the fuzzy coma around it.
Since the coma isnt solid, it doesnt have a sharp edge. But on Nov. 15, the coma for ISON was estimated to appear about 3 arcminutes across (thats a size on the sky; the Moon is 30 arcminutes across for comparison). Since ISON was about 140 million km (90 million miles) from Earth at the time, that would put the coma at a size of about 120,000 km (80,000 miles). Thats ten times the diameter of Earth!
6) The tail of the comet is (at least) 8 million kilometers long.
Comet ISON on Nov. 12, 2013. Photo by Michael Jäger
Once the gas (and ejected dust) in the coma is out in space, it can be affected by both the solar wind and the pressure of sunlight. It streams away, forming one or more long tails. Like the coma, this is extremely rarefied gas, so it doesnt really have an edge, but the tail of ISON has been measured to be at least 8 million km (5 million miles) long. Thats 20 times the distance of the Moon from the Earth.
7) The tail is essentially a vacuum.
Weirdly, despite being bright and obvious, a comets tail is incredibly ethereal. The density of atoms in a typical tail can run up to about 50,000 atoms per cubic centimeter. Sound like a lot? In a cubic centimeter of air at sea level, there are 10[SUP]19[/SUP] (10,000,000,000,000,000,000) atoms/molecules per cc! Compared to the air we breathe, a comets tail is a hard vacuum. Its only bright because its so big, and reflects sunlight.
The total mass of the comet is about 2 - 3 billion tons.
Ice isnt terribly dense; it floats on water! If ISON is a typical mix of ice and rock, it has a density of about 600 kg per cubic meters. Assuming its a sphere two km across, that gives it a mass of roughly 2 - 3 billion tons. That may sounds like a lot, but remember, ice is far less dense than rock. A small rocky mountain would be far more massive.
[Comet ISON over a 70-minute period on Nov. 14, 2013, taken by Bruce Gary].
9) ISON is shrinking.
Measurements of how much water ice is leaving the comets surface indicate its losing about 10[SUP]29[/SUP] molecules of water every second (bearing in mind this goes up and down all the time). Doing the math, I get that this is about three tons per second enough to fill an Olympic pool in about ten minutes. Thats a fair amount, but given the total mass of the comet, it would take about 25 years at this rate for the comet to totally disappear. Since its only shedding mass for the few weeks its near the Sun, its got mass to spare. Thanks to @SungrazingComets and the Comet ISON Observing Campaign for their help with this.
10) ISON may disintegrate
ISON sprouts "wings"! The arcs above and below the nucleus are common when pieces of a comet break off. In this case, though, no fragments were seen. Photo by Wendelstein Observatory of the LMU / MPS
That doesnt mean its safe, though! Some comets arent terribly solid; the ice is what holds them together. As they near the Sun and the ice starts to go away, big chunks can break off (called calving). In some cases the comet can disintegrate spectacularly. Even if they survive their plunge down to the Sun, some comets get so close they evaporate; weve seen that happen too!
Its not clear if ISON will survive its close shave with the Sun. As of right now it seems to be OK, but who knows what the next few days will bring.
11) ISON wont hit the Earth.
Nope. Photo by Shutterstock / buradaki (modified by Phil Plait)
Whenever theres a bright comet (or near pass of an asteroid), conspiracy buffs start thinking itll hit us. Dont worry about ISON. The closest it will get is on Dec. 26, 2013, when it will be about 60 million km (40 million miles) from Earth. Thats 150 times farther away than the Moon.
12) You can see it for yourself, and it may become visible in broad daylight.
Comet Pan-STARRS (between the trees, under the jet contrail) shortly after sunset on Mar. 19, 2013. Photo by Phil Plait
Right now, ISON is bright enough to see naked eye, and easily with binoculars. Its jumped in brightness twice just in the past week or so! As it gets near the Sun itll get brighter, but harder to find because, duh, its getting near the Sun.
However, sometimes comets like this get incredibly bright when they are close to the Sun. In 2007, I saw comet McNaught at noon. Yes, noon. It was difficult, and I had to be very careful; you dont want to wind up looking right at the Sun, especially in binoculars, unless boiled eyeballs is something you want. Seriously, dont just scan around with binoculars looking for the comet, because its very dangerous and can blind you.
Theres no way to know right now, but its possible that ISON will be visible in broad daylight to the naked eye for the short time its near the Sun. It could be possible to see it during the day if you position yourself so that the Sun is blocked behind a tree, or the edge of a house. It depends on the exact position of the comet relative to the Sun, of course.
Again, doing this is difficult and you shouldn't attempt it unless you know what youre doing. Ill note that in general, glancing briefly at the Sun wont hurt a normal eye with an undilated pupil, but its not a good idea to do it too much, and its more dangerous for kids (their lenses let through more UV light than adult eyes).
Your better bet is to wait a few more days. Once ISON rounds the Sun, itll be visible in the west after sunset for a few weeks for those of us in the northern hemisphere, so watching it will be far easier (right now you have to get up at about 5:00 a.m., before sunrise, to see it). Heres a finder chart (Sky and Telescope has another as well) thatll help you spot it; planetarium software for mobile devices are great too (I like Sky Safari, but there are many to choose from). You can find plenty more finder charts online. Ill note itll fade with time, but around Dec. 20 or so it should be out of the Suns glare, and (hopefully) easily visible with binoculars. [UPDATE (Nov. 22, 2013 at 16:15 UTC): I'll note that once it passes the Sun, the comet will still be visible in the east before sunrise in the morning as well as in the west after sunset in the evening. I explain this in a follow-up post.]
some facts about it...
from..
http://www.slate.com/blogs/bad_astronomy/2013/11/21/comet_ison_12_cool_facts.html
1) ISON is a n00b.
Some comets are on long, elliptical orbits dropping them in to the inner solar system before sailing them back out to the depths of space. There, they slow, stop, then fall once again back into the warmth and light. Comet Halley, for example, is on a 75-year orbit that takes it out past Neptune.
But some are more extreme. If they get an extra kick on their way in perhaps from a collision, or a boost by a planets gravity their elliptical orbit gets turned into an open-ended hyperbola: they have more than enough energy to leave the solar system forever. Once theyre gone, theyre gone.
ISON is a hyperbolic comet, which means this is it: These next few weeks are our only chance to see it. After it swings back out, it aint coming back. This is likely its first tour of the inner solar system as well, which is why scientists are so excited about it; were seeing a pristine comet, billions of years old, a relic of the ancient solar system. Its a time capsule, letting us study what conditions were like when the Sun and planets were young.
2) ISON is a sun-diver.
The orbit of ISON passes very close to the Sun. This diagram shows what NASA/ESA's SOHO satellite will see; the various circles are the different fields of view of SOHO's cameras. Photo by NASA / ESA / SOHOThe orbit of ISON takes it very, very close to the Suns surface. Next week, on Nov. 28, it will skim a mere 1.1 million kilometers (about 700,000 miles) above the Suns surface. Given that the Sun is 1.4 million km across, thats a mighty close shave! The heat it feels will be intense, and it may not survive the encounter (see #10 below).
3) When it passes the Sun, it will be moving at 360 kilometers per second.
Imagine dropping a rock. The higher you drop it, the longer the Earths gravity has to pull on it, and the faster itll be moving when it hits the ground.
The fastest a rock can hit the Earth is if you drop it from infinitely far away. When it hits itll be moving at escape velocity and the physics of dropping it is reversible, so if you throw a rock at escape velocity it will continue on forever (hence the term "escape velocity").
Comet SWAN (left) on a death dive into the Sun in 2012. Photo by NASA / ESA / SOHOThe same is true for a comet rounding (or, in some cases, impacting) the Sun. Since ISON is falling from essentially infinitely far away, when it goes around the Sun itll be moving at the Suns escape velocity at that distance, or just about 360 km/sec (225 miles/sec). How fast is that? Well, it's hundreds of times faster than rifle bullet, for example, and over 1500 times faster than a commercial jet at that speed, the comet would cross the continental United States in about 15 seconds.
In fact, it will be moving at 0.1% the speed of light! Thats far faster than any human-made space probe has ever traveled. And the only propulsion it uses is gravity.
[CORRECTION (Nov. 22, 2013 at 16:15 UTC): I made an error in the calculation for this section, using the escape velocity for the Sun's surface, and not for the distance ISON will be from the Sun's center. This deserves a longer explanation, so I wrote a follow-up post about it, and simply corrected the problem here.]
4) The solid part of ISON is only about two kilometers across.
The nucleus of comet Hartley 2, seen up close during a flyby of the EPOXI spacecraft in 2010. You can see jets of material (ice turning into gas) from pockets on the surface. Photo by NASA / JPL-Caltech / UMDComets are actually lumps of rock, gravel, and ice mixed together. This solid part of the comet is called the nucleus, and some are huge; Hale-Bopp had a nucleus about 30 km (20 miles) across.
ISON, though, is tiny, only about 2 km (1.2 miles) across. Heck, plop it down in the middle of the Rocky Mountains and youd hardly notice it! The size has been estimated using images taken from the Hubble Space Telescope, which in reality only give us an upper limit. It might even be smaller.
Still, thats enough to make the comet visible to the naked eye even from a distance of a hundred million kilometers! How can that be? Why, its because
5) The coma is well over 100,000 km in size.
A very rough comparison of the physical size of ISONs coma and the Earth. On this scale, the solid nucleus of ISON would be about the size of a bacterium. Comet photo by Damian PeachWhen you look at a picture of ISON (or any comet), youre not seeing the nucleus. Youre seeing the gas surrounding it that was once frozen beneath the surface. When the comet gets near the Sun this ice warms and turns directly into a gas. It escapes the weak gravity of the nucleus, forming the fuzzy coma around it.
Since the coma isnt solid, it doesnt have a sharp edge. But on Nov. 15, the coma for ISON was estimated to appear about 3 arcminutes across (thats a size on the sky; the Moon is 30 arcminutes across for comparison). Since ISON was about 140 million km (90 million miles) from Earth at the time, that would put the coma at a size of about 120,000 km (80,000 miles). Thats ten times the diameter of Earth!
6) The tail of the comet is (at least) 8 million kilometers long.
Comet ISON on Nov. 12, 2013. Photo by Michael JägerOnce the gas (and ejected dust) in the coma is out in space, it can be affected by both the solar wind and the pressure of sunlight. It streams away, forming one or more long tails. Like the coma, this is extremely rarefied gas, so it doesnt really have an edge, but the tail of ISON has been measured to be at least 8 million km (5 million miles) long. Thats 20 times the distance of the Moon from the Earth.
7) The tail is essentially a vacuum.
Weirdly, despite being bright and obvious, a comets tail is incredibly ethereal. The density of atoms in a typical tail can run up to about 50,000 atoms per cubic centimeter. Sound like a lot? In a cubic centimeter of air at sea level, there are 10[SUP]19[/SUP] (10,000,000,000,000,000,000) atoms/molecules per cc! Compared to the air we breathe, a comets tail is a hard vacuum. Its only bright because its so big, and reflects sunlight.
The total mass of the comet is about 2 - 3 billion tons.Ice isnt terribly dense; it floats on water! If ISON is a typical mix of ice and rock, it has a density of about 600 kg per cubic meters. Assuming its a sphere two km across, that gives it a mass of roughly 2 - 3 billion tons. That may sounds like a lot, but remember, ice is far less dense than rock. A small rocky mountain would be far more massive.
[Comet ISON over a 70-minute period on Nov. 14, 2013, taken by Bruce Gary]. 9) ISON is shrinking.
Measurements of how much water ice is leaving the comets surface indicate its losing about 10[SUP]29[/SUP] molecules of water every second (bearing in mind this goes up and down all the time). Doing the math, I get that this is about three tons per second enough to fill an Olympic pool in about ten minutes. Thats a fair amount, but given the total mass of the comet, it would take about 25 years at this rate for the comet to totally disappear. Since its only shedding mass for the few weeks its near the Sun, its got mass to spare. Thanks to @SungrazingComets and the Comet ISON Observing Campaign for their help with this.
10) ISON may disintegrate
ISON sprouts "wings"! The arcs above and below the nucleus are common when pieces of a comet break off. In this case, though, no fragments were seen. Photo by Wendelstein Observatory of the LMU / MPSThat doesnt mean its safe, though! Some comets arent terribly solid; the ice is what holds them together. As they near the Sun and the ice starts to go away, big chunks can break off (called calving). In some cases the comet can disintegrate spectacularly. Even if they survive their plunge down to the Sun, some comets get so close they evaporate; weve seen that happen too!
Its not clear if ISON will survive its close shave with the Sun. As of right now it seems to be OK, but who knows what the next few days will bring.
11) ISON wont hit the Earth.
Nope. Photo by Shutterstock / buradaki (modified by Phil Plait)Whenever theres a bright comet (or near pass of an asteroid), conspiracy buffs start thinking itll hit us. Dont worry about ISON. The closest it will get is on Dec. 26, 2013, when it will be about 60 million km (40 million miles) from Earth. Thats 150 times farther away than the Moon.
12) You can see it for yourself, and it may become visible in broad daylight.
Comet Pan-STARRS (between the trees, under the jet contrail) shortly after sunset on Mar. 19, 2013. Photo by Phil PlaitRight now, ISON is bright enough to see naked eye, and easily with binoculars. Its jumped in brightness twice just in the past week or so! As it gets near the Sun itll get brighter, but harder to find because, duh, its getting near the Sun.
However, sometimes comets like this get incredibly bright when they are close to the Sun. In 2007, I saw comet McNaught at noon. Yes, noon. It was difficult, and I had to be very careful; you dont want to wind up looking right at the Sun, especially in binoculars, unless boiled eyeballs is something you want. Seriously, dont just scan around with binoculars looking for the comet, because its very dangerous and can blind you.
Theres no way to know right now, but its possible that ISON will be visible in broad daylight to the naked eye for the short time its near the Sun. It could be possible to see it during the day if you position yourself so that the Sun is blocked behind a tree, or the edge of a house. It depends on the exact position of the comet relative to the Sun, of course.
Again, doing this is difficult and you shouldn't attempt it unless you know what youre doing. Ill note that in general, glancing briefly at the Sun wont hurt a normal eye with an undilated pupil, but its not a good idea to do it too much, and its more dangerous for kids (their lenses let through more UV light than adult eyes).
Your better bet is to wait a few more days. Once ISON rounds the Sun, itll be visible in the west after sunset for a few weeks for those of us in the northern hemisphere, so watching it will be far easier (right now you have to get up at about 5:00 a.m., before sunrise, to see it). Heres a finder chart (Sky and Telescope has another as well) thatll help you spot it; planetarium software for mobile devices are great too (I like Sky Safari, but there are many to choose from). You can find plenty more finder charts online. Ill note itll fade with time, but around Dec. 20 or so it should be out of the Suns glare, and (hopefully) easily visible with binoculars. [UPDATE (Nov. 22, 2013 at 16:15 UTC): I'll note that once it passes the Sun, the comet will still be visible in the east before sunrise in the morning as well as in the west after sunset in the evening. I explain this in a follow-up post.]
