Obscure Comet Brightens Suddenly

Originally posted by Hal9000
That is farther away than Mars, so in order to be able to hit the comet, the mission to do so would have had to be launched a year and a half ago in order to hit the comet on the 23rd.

I don't want to be a party pooper, but what if they used a super secret high powered photon beam weapon...?

Originally posted by mythatsabigprobe
I don't want to be a party pooper, but what if they used a super secret high powered photon beam weapon...?

Do you mean one of Ronny's ray guns?

Well, if they could make one powerful enough, then all bets are off, and would also beg the question...Why?

I’ve been reading some incredible numbers with regard to the actual size of the coma of Comet 17P/Holmes, so I thought I would try to calculate it myself. Even though the comet nucleus is only 3.4 km in size, I’ve heard that the coma was seven times the size of Jupiter (1) and I also heard it was the size of the orbit of the Moon. I found one example of how to calculate the size on a forum, but the apparent size was wrong, so I did them myself from numbers I found in recent articles.

On Sky and Telescope (2) they said the apparent size of the coma as it looks in the sky was 10 arc minutes on Oct. 31, and from the JPL 3D orbital simulator (3), on Oct.31 the distance of the comet was 1.624 AU. So starting with these numbers I did the following calculations.

1 astronomical unit (AU) = 149,597,870 km
Distance to the comet = 1.624 AU
Distance to the comet = 242,946,941 km

Apparent size of coma = 10 arcmin
Apparent size of coma = 0.167 degrees
Apparent size of coma = 0.0029089 radians

Actual size of coma = the sine of the angle in radians times the distance
Actual size of coma = SIN(0.0029089) * 242,946,941 km
Actual size of coma = 706,703 km or 439,125 miles

Size of Jupiter = 142,800 km
This works out to be almost 5 times the width of Jupiter.

1 Lunar Distance (LD) = 384,403 km
Actual size of coma = 1.84 LD
This works out to be about 90% of the size of the Moon’s orbit.

So what I’ve been hearing is right. The coma is incredibly huge.

If anyone can find a problem with these calculations, let me know.


1) Spaceweather.com claiming the coma is seven times wider than Jupiter on Nov.1.
www.spaceweather.com...

2) Sky and Telescope article giving apparent size of 10 arcmin as of Oct.31.
www.skyandtelescope.com...

3) JPL 3D Orbital simulator giving distance at 1.624 AU on Oct 31.
ssd.jpl.nasa.gov...

edit: I have a correction to make.

The diameter of Jupiter is 142,800 km not 71,492 km, so that means the coma of the comet is the width of FIVE Jupiters not 10. I have changed the numbers accordingly.

[edit on 11/3/2007 by Hal9000]

Originally posted by NuclearPaul
WOW! The comet suddenly and unexpectedly brightens after 23rd October. What a coincidence the space shuttle was launched, against safety advice, on this day! Did they not send an explosive device into the Tempel comet in 2005? Scientists are speculating why the comet has "exploded". Come on...

Are you inplying that the shuttle launched some kind of probe toward the comet to blow it up?

Comet Holmes is somewhere between the orbits of Mars and Jupiter, and is almost on the other side of the sun from us. There is no way that any probe launched from the Shuttle could have gotten there that quickly (it would have taken months.)

Since this comet has a history of brightening like this (it did something similar in 1892), what makes you think that this time we humans had something to do with it?

And, by the way, they did not send "explosives" to Tempel 1. The probe that hit Tempel 1 did not have any explosives on board. Think of the probe as being a "bullet" or a high speed projectile that "smashed into" Tempel 1 (like shooting a rock with a rifle bullet.)



[edit on 11/3/2007 by Soylent Green Is People]

reply to post by Hal9000


Thanks for doing the calculations. I was getting confused myself by the many different ways of describing the size of this thing.

So its coma really is 10 times the diameter of Jupiter? Thats quite incredible, considering the size of Jupiter...

Jupiter is so large that it is hard for us to grasp just how big it is. Jupiter is about 142800 kilometers. in diameter, dwarfing Earth, which is about 12800 kilometers. in diameter. Jupiter is so large that 1300 Earths could fit inside it. Put another way, if you had a ball that was about the size of 10 cents, Jupiter would be the size of a soccer ball.

Source

And still growing it seems.

I found another site which backs your calculations up: Linkage. The guy says "The diameter has doubled since my last image 3 days ago".

Very interesting.


[edit on 3-11-2007 by Copernicus]

reply to post by Copernicus

Someone pointed out I had the wrong diameter for Jupiter and have made a correction. The size comes out to be 5 Jupiters wide not 10.

Also keep in mind the values are from Oct. 31, so it has expanded since then so others may have different numbers.

Any way you look at it, it's friggin huge.

edit: I was just out at the astronomy club and our president told me he was told the outer coma was 20 arc minutes wide, so now we are back to the size of 10 Jupiters. He said that the coma is divided up into layers and the size depends on which one you are referring to. Very confusing.

To put it into perspective, the Moon and Sun both have an apparent size of 30 arc minutes, so the outer coma is about 2/3rds the size of either of them.

[edit on 11/3/2007 by Hal9000]

www.Spaceweather.com has great information and pictures. Very good site.

?

Are there any photos of the comet taken from Hubble,
the ISS or SS Discovery ?? If not, why not ??


?

Originally posted by mythatsabigprobe
I don't want to be a party pooper, but what if they used a super secret high powered photon beam weapon...?

I am looking for those... care to link me to yours?

Well it's a secret.

You know how that goes.. if I told you I'd have to kill you.

reply to post by Hal9000


Yeah. Thats one big comet.

Even if there was a explosion, how do science explain that the coma has been growing for almost two weeks now?

reply to post by Copernicus

Some scientists say that a "collapse" or cracking of the surface of the surface of the comet could have exposed a sub-surface batch of ice that is being excited by the Sun's radiation, and is only now thus forming a huge cloud of gas.

Most comets flare up as they approach the sun, as their icy surfaces become heated. The difference with Holmes is that the ice may not have been exposed to the sun during it's approach, and is only now exposed to the Sun while it is moving away, because of the possible collapse of the surface.


EDIT TO ADD:
reply to post by Ivanova

Comet Homes is hundreds of Millions of miles away from us (it is between the orbits Mars and Jupiter). While it is true that the shuttle and ISS are in space, and thus don't need to look through the atmosphere when viewing an object, it is also true that the astronauts don't have powerful telescopes like we have on Earth. Since the ISS and the shuttle are only 200 miles in space, they are not really any closer to the comet, therefore a ground-based powerful telescope can get much better images that the orbiting astronauts.

As for Hubble...astronomers' viewing time on the Hubble telescope is in much demand and is scheduled years in andvance. Quite frankly, this comet is not important enough for those astronomers to give up their viewing time for their important projects. For some of these astronomers, their whole careers ( and the grant money they received) can hinge upon the short time they have been alotted using the Hubble Telescope. They don't want to give that up.

By the way, this is also true (but to a lesser extent) of the most powerful Earth-based telescopes. That is why most of the Comet Holmes photos have been from amateur astronomers.

[edit on 11/4/2007 by Soylent Green Is People]

reply to post by Copernicus

To add to what Soylent Green Is People explained, you have to keep in mind the comet nucleus is very small at 3.4 km. Because of the small mass and no atmosphere, it will not have any gravity like any planet so anything that shoots out of the nucleus will have no resistance, so it will continue to expand into space. As the vapor expands it is becoming less dense and is now starting to dim. I think after the main eruption, there is still a slow fizz happening, so the outer coma may dim out, but we may be able to see the comet center longer.

reply to post by Ivanova

I know Hubble was tasked on Oct.26th according to the following schedule.

2007.302 12:18:24 13:06:32 1141801 Weaver 01-001 17P-HOLMES WFPC2 IMAGE PC1-FIX F675W 400.00 01 01 02
2007.302 12:18:24 13:06:32 1141801 Weaver 01-002 17P-HOLMES WFPC2 IMAGE PC1-FIX F555W 400.00 01 01 03
2007.302 12:18:24 13:06:32 1141801 Weaver 01-003 17P-HOLMES WFPC2 IMAGE PC1-FIX F555W 40.00 01 01 04
2007.302 12:18:24 13:06:32 1141801 Weaver 01-004 17P-HOLMES WFPC2 IMAGE PC1-FIX F675W 40.00 01 02 02
2007.302 12:18:24 13:06:32 1141801 Weaver 01-005 17P-HOLMES WFPC2 IMAGE PC1-FIX F675W 400.00 01 02 03
2007.302 12:18:24 13:06:32 1141801 Weaver 01-006 17P-HOLMES WFPC2 IMAGE PC1-FIX F555W 400.00 01 02 04

www.stsci.edu...

I have not seen any images released yet, but when they do the images will probably be released on this site and I'm sure it will also appear on other astronomy news sites.


[edit on 11/4/2007 by Hal9000]

reply to post by C.H.U.D.


What I would like to know is why this comet can be seen to have different colours depending on who is photographing it? Just browsing through the pictures of it and you see it being blue, white, yellow, green etc.

Originally posted by mythatsabigprobe
Well it's a secret.
You know how that goes.. if I told you I'd have to kill you.

Yes I KNOW how that goes... but you have the line wrong... its really

"If I tell you, then they will shoot me, after my family and my dog..."

So how about you show me yours and I will show you mine? And I promise not to tell... really

Originally posted by Hal9000
I have not seen any images released yet, but when they do the images will probably be released on this site and I'm sure it will also appear on other astronomy news sites.

Or here...

hubblesite.org...

I've emailed my question to my brother who is a NASA scientist...
but I am not counting on getting much information from him either...
after all... although he is one of NASA's experts on deep space objects...
he does work for the government.

Originally posted by Copernicus
What I would like to know is why this comet can be seen to have different colours depending on who is photographing it? Just browsing through the pictures of it and you see it being blue, white, yellow, green etc.

Quite a few factors would influence this, including what camera/telescope/lens was used (and settings such as white balance). Then there is the sky conditions... from a dark rural location the sky would be free from artificial light pollution for instance.

The length of the exposure also plays a large part, especially by bringing out faint colors present in the coma and ion tail in the case of long exposures.

Post-processing techniques and work flow might also play a part. It's up to the photographer to decide what the final color should be, and I think most aim to reproduce what they saw through the view-finder as faithfully as possible, although in some cases such as the fainter colors which need long exposure times to be seen, this is obviously not possible.

With all those variables, (and lets not forget this is a transient event, so parts of the comet could be undergoing subtle changes in color) it's not surprising that no two photos look the same! In any case, if we want accurate color, there are always diffraction gratings, and the "normal" photographs can be still be used to give us clues about the fine structure and evolution of this phenomenon.

I would always caution anyone looking at any astronomical photograph, that in many cases the color may not be accurate, and in some it is entirely false, the photo having been taken by capturing wavelengths of light that our eyes are not even sensitive to.

Just saved an image of the comet tonight from Slooh.com. Very nice.