

New comet might blaze brighter than the full Moon - tartarugafeliz
http://www.astronomynow.com/news/n1209/25comet/

======
tzs
I'm getting a little disappointed with astronomical events. The let downs have
greatly outnumbered those that have delivered.

DISAPPOINTMENTS:

Comet Kohoutek

Halley's Comet

Every meteor shower I've watched: at least an order of magnitude less than
they said I might see.

SUCCESSES:

Comet West: this one delivered. It wasn't a big comet, but it was bright and
beautiful in the dawn.

1975 nova in Cygnus: <http://en.wikipedia.org/wiki/V1500_Cygni>

FALSE ALARM:

I saw a very bright star-like object, fairly low in the sky. It was around
magnitude -4 or -5, much brighter than any normal star. This was in the east,
and it was around 10pm, so it could not be Venus. I watched for several
minutes and could detect no movement. I grabbed some binoculars for a closer
look. It still appeared as a point source, and still showed no movement.

I watched for a bit more and it finally started showing movement, ruling out
my guess that I was seeing a supernova.

Turns out it was a B-52, very far away, coming straight at me with its landing
light on. Those lights are quite powerful, and you can see them when the plane
is a couple hundred miles away or more. We lived about 5 miles from the
runways at Castle Air Force Base, and from where the plane was the angular
distance between me and the runway from the plane's point of view would have
been maybe half a degree, so it's not surprising that there would be an
occasional B-52 coming right at me.

~~~
jlgreco
Hale-Bopp in 1997 was very nice, as I recall.

~~~
rhizome
Naked-eye, even.

------
tokenadult
This would be very cool if it happened. I still remember spending all of my
childhood after learning to read waiting for Comet Halley to return, and then
having difficulty seeing it even in the desert of Arizona. Now I refer to that
comet as "Halley's Smudge." Comet Hale-Bopp was all right, and well visible
from Boston Common on a fine spring evening in 1997 when I was there on a
business trip. Simply put, predicting the visibility of a comet to the naked
eye is more wild guess than science, but when a comet is visible, it is a
delight to the eye.

AFTER EDIT, EXPLANATION OF ASTRONOMICAL MAGNITUDE SCALE:

[http://outreach.atnf.csiro.au/education/senior/astrophysics/...](http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_magnitude.html)

<http://www.icq.eps.harvard.edu/MagScale.html>

[http://csep10.phys.utk.edu/astr162/lect/stars/magnitudes.htm...](http://csep10.phys.utk.edu/astr162/lect/stars/magnitudes.html)

[http://www.skyandtelescope.com/howto/basics/Stellar_Magnitud...](http://www.skyandtelescope.com/howto/basics/Stellar_Magnitude_System.html)

Oddly, the historically developed magnitude scale (which goes back to the
ancient Greek astronomers) has the brightest objects ranked with magnitudes
that are negative numbers, and dimmer objects ranked with increasing numbers
that eventually become positive numbers. Of course the estimate of eventual
brightness of the newly discovered comet is just that, an estimate, and may
disappoint.

~~~
jeangenie
FYI the Greeks didn't have negative numbers. Philosophers were still arguing
whether zero could truly be a number (there wasn't really a need for zero as a
placeholder regardless, Greek numerals don't have a positional aspect).

Source: [http://www-history.mcs.st-
and.ac.uk/HistTopics/Greek_numbers...](http://www-history.mcs.st-
and.ac.uk/HistTopics/Greek_numbers.html)

------
Stratoscope
When I was five or so, my dad got excited one day and said there would be a
comic in the sky and we would go see it that night. I thought that was pretty
cool, and I thought about how they were going to set it up.

I'd seen searchlights many times used for advertising where you could see the
beam hit the bottom of an overcast, and I figured they had a way to use one of
those to actually project a comic up onto the cloud cover.

After dark, we drove out of town up to a hilltop. I was puzzled: it was a
perfectly clear night, so what were they going to project the comic onto?

Then he pointed and said, "There it is!"

But it was no comic, it was just a little star with a fuzzy tail.

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wtvanhest
Quick question for someone who knows more about this stuff. Is brightness
adjusted for size?

In other words: If the comet is 20% the size of the moon and the same
brightness, is it throwing off 20% as much light due to the lower surface
area?

~~~
z92
Brightness published for this comet in the article is in "magnitude" and it's
a logarithmic value of total brightness as used in astronomy. Not brightness
per unit area.

~~~
wtvanhest
So if the comet is much smaller than the moon, is it reasonable to assume that
it wouldn't reflect enough light to light the earth's surface like a full
moon?

~~~
Dylan16807
Why did you just ask the same question again? I guess you couldn't tell what
z92 meant?

Anyway the answer to your question is no. The article is talking about total
light, in Watts. Area is not a factor.

~~~
wlesieutre
Watts is not a useful measure of visibility for humans, I would hope they're
using lumens. Unless it's safe to assume that it reflects very similar amounts
of visible light to the moon, but I don't know if that's the case.

~~~
bostonpete
Isn't light a synonym for visible light...?

~~~
wlesieutre
In most contexts. But it's used frequently in "infrared light" too. Watts
include radiation across the entire EM spectrum, from radio up to gamma rays,
while lumens are normalized to human perception.

You basically take the number of watts at each wavelength and multiply it by a
factor that represents the eye's sensitivity at that wavelength. So 1 watt of
IR is zero lumens, and 1 watt of blue light is fewer than 1 watt of yellow.

Take a look at the spectral distribution of daylight [1]. You'll notice the
area under the curve in IR is pretty similar to the amount of visible light.

If the IR reflectivity of a comet were high and the visible were low (relative
to the moon), knowing that they were reflecting about the same wattage
wouldn't tell you much about relative brightness.

[1]
[https://upload.wikimedia.org/wikipedia/commons/4/4c/Solar_Sp...](https://upload.wikimedia.org/wikipedia/commons/4/4c/Solar_Spectrum.png)

------
T_S_
Anybody remember Kohoutek? Exactly. If I were a comet, my strategy would be to
underpromise and overdeliver. That's the best way to rally a comet's
soothsayer base.

~~~
groby_b
If you talk about this approach, the first commet that comes to mind is
Hamner-Brown. (Yeah, it's fictional. Still, it's the archetype of that
strategy :)

~~~
robterrell
Ha! I remember that book. I memorized several end-of-the-world survival
strategies from it. Like "you can drive a jeep on railroad tracks" and "when
packing for the apocalypse, don't forget liquor."

~~~
groby_b
Yeah. I keep telling myself I'm simply disaster-ready when I look at my liquor
cabinet, too :)

------
R_Edward
Then again, it might not. In any case, I'm polishing up my Galilieoscope and
hoping for the best. ("The best" meaning that I don't actually need my
Galileoscope, because I find it particularly difficult to aim and focus.)

~~~
cryptoz
I also have a Galileoscope. I find it really awesome if you use a tripod, but
otherwise totally miserable. And even with the tripod...yeah, focusing is
tough. But possible, and very very rewarding for a $15 scope.

------
ericxb
I predict that when the world doesn't end in December 2012 the doomsdayers
will latching on to this thinking the Mayans were off by a year and that this
comet will cause the end of the world.

~~~
DougWebb
I agree... this is going to have huge "star of Bethlehem", "Second coming",
and "we were off by a year on Mayan calendar" connotations. The timing is just
too perfect.

So... who's going to start a company to take advantage of this?

~~~
Raphael
Late to market. The myriad of religious institutions have it cornered.

------
genwin
Excellent! Hale-Bopp was so cool to see. I was hoping for a another great
comet to show my son.

------
andershaf
I'm not sure if this is correct. The moon has an average apparent magnitude of
-12.74 (which is a lot, you've seen it), and as Wiki says:

'At the time of its discovery, the comet's apparent magnitude was about 18.8'.
That's PLUS 18.8, but allright, at the time of its discovery.

...

'The comet may become extremely bright if it remains intact, probably reaching
a negative magnitude.'

If the comet reaches a magnitude of -1, the moon is more than ten billion
times brighter! I don't believe the uncertainty is within a factor 10^10, so
this is probably just bad journalism.

~~~
genwin
I think the article is saying that the predicted magnitude of the comet is
-16.

~~~
andershaf
Yes the article says so, but I really don't believe that it's correct. The
comet will at its closest be around 60,000,000 km away from the earth, that is
more than 150 times further away than the moon, and almost halfway to the sun.

What could possibly make the comet, which is very, very small compared to the
moon, be that bright? I think the journalist have misunderstood the
calculation or maybe read ~16 (approximately, which has been the current
magnitude) as -16.

From nasa.gov: "In the best case, the comet is big, bright, and skirts the sun
next November. It would be extremely bright -- negative magnitudes maybe --
and naked-eye visible for observers in the Northern Hemisphere for at least a
couple of months."

If NASA says it _might_ reach negative magnitudes, I'm pretty sure the -16 is
wrong.

~~~
ballooney

      What could possibly make the comet, which is very, very small compared to the moon, be that bright?
    

The tail, which is very, very big compared to the moon.

------
mhurron
Come on Universe, show us something unusually spectacular. A once in a
lifetime, awe inspiring event. Something wondrous to let people for a moment
see just how amazing everything around them is.

Honestly, I'm really hoping this comet hits closer to the fantastic side of
the predictions. Also hoping to be able to see it from the eastern US. It says
Northern Hemisphere observers are favored, so there's even more hope.

~~~
run4yourlives
Personally, I'm gunning for Betelgeuse. That would be awesome.

[http://en.wikipedia.org/wiki/Betelgeuse#Approaching_supernov...](http://en.wikipedia.org/wiki/Betelgeuse#Approaching_supernova)

~~~
russell
My personal favorite is Eta Carinae which could be 20 times the size of
Betelgeuse and may be big enough to be a hypernova. It may explode in our
lifetimes. Pretty pictures at <http://en.wikipedia.org/wiki/Eta_Carinae>

------
ianterrell
The dragons really are coming back to Westeros.

~~~
almog
The comet only means one thing, boy ;-)

~~~
HorizonXP
I just watched this episode today. Came here to find this comment, was not
disappointed.

Of course, this means that HN is becoming more like Reddit. :-P

------
anovikov
Just don't forget that -16 mag will happen VERY close to the sun. Comet won't
be visible from Earth at that time even at that magnitude, while it will be a
cool sight for SOHO cameras, possibly blinding the sensor.

