Starship Asterisk*

badsocref, the simulation is amazing. I really appreciated it. Although, my question has not been explained, can anyone? Do the publishers of APOD just take the stars out? No. The image is exposed to show the Earth and the lunar surface, which are many, many times brighter than the stars. The stars...

I didn't realize Holmes, (and I appreciate your calling it Holmes and not Comet Holmes) only orbited the Sun between the orbits of Jupiter and Mars, so it therefore does not qualify to be called a Comet, like all the media is calling it. It is a comet by any accepted definition. Comets are just sma...

How does one define the "edge" from which one determines the size of the coma? Is the "edge" of the coma where light transmissivity falls below some value for some frequency, or is it where the particle density falls below some # per m**3 or what? Is this also the standard defin...

Today's APOD still has the size of Holmes's coma wrong. As of Nov 21, the diameter of the dust coma is 3 million kilometers. On the date of the image, Nov 14, the diameter was 2.1 million kilometers. If you include the region of gas outside the dusty coma, those diameters are even larger. My profil...

One possibility is that the photos were not taken on the stated date. They might have been taken years before. But in Alaska early on the morning of 4 October 2007, the Moon was just past its last quarter; this is consistent with its culminating sometime in the wee hours before sunrise. Note that t...

Is the 'dust' of Holmes' coma 'finely divided' dust? I'm not sure what you mean by that, but the dust is certainly very fine. I'm planning on trying to estimate the size of the dust using the basic equations defining comet dust ejection velocities, but haven't had time yet for this. Has there been ...

Could your word 'gas' also be a euphemism for 'plasma'. If Holmes is outgassing plasma, the Sun's electric field in the solar system, which accelerates the solar wind, would also be accelerating Holmes' outgassed plasma. This would easily explain why the coma is increasing its size at an increasing...

Reports about the comet tend to run a little late, but today's APOD is substantially off in its estimate of coma size. As of November 17, the dust coma is 2.5 million kilometers in diameter, not 1.4 million. That makes it 80% larger than the Sun. I've been measuring the growth since the first day of...

1.) Launch tugs to deorbit old satellites (spendy...might be able to piggy back the tug with the replacement satellite). Most geostationary satellites are operational. It is part of their mission design that when they reach the end of their service life, they are boosted into a slightly higher orbi...

The APOD caption says it was a meteor, but I remember watching Cosmos when Carl Sagan was talking about it, and he said it was a piece of a comet. He even named the comet, but I don't remember the name now. A meteor is the energetic release of energy in the atmosphere by a high velocity object from...

Is it not the case that the only mechanisms for cometary activity is sunlight light pressure and heat, collisions and close encounters with planets ? Depends what you mean by "activity". Certainly, all those things can influence the appearance of a comet. But by far the dominant mechanism...

but what a sight in the night sky I think most of what is going on would be invisible from either galaxy, just as most of our own galaxy is invisible to us. You'd certainly see nothing in the sky brighter than the Milky Way, although from the inner edge of the galaxy on the right, it looks like you...

in the full resolution picture, there are three background galaxies in a line more-or-less tangent to the top of the face-on galaxy. i'd expect more-distant galaxies to be both smaller in apparent size and more red-shifted in colour. why then is the one on the right both bigger and redder than the ...

Isn't it possible that the "Halo" that we are seeing IS the tail ? I don't think so. A comet's tail isn't a simple cone, but a complex, structured collection of individual streams. We have simply been seeing the expanding coma. The tail is pointing away from us, and hints of it have been ...

yahoooooooo the tail has a comet attached. I just found the pictorial of the orbit and it is way above the ecliptic. Assuming a lot of dust in the ecliptic plane, does that imply increased sunlight above ( or below ) the ecliptic ? It seems like this comet is reacting quite strongly despite the gre...

Many comets have two tails, one dust, the other plasma (?- electrically charged, anyway) that curves. If we can't see that curving tail, then Holmes doesn't have one. What does this tell us about Holmes? Both a dust tail and ion tail are starting to show up in images. Presumably, the comet's distan...

So far so good, but I still have a bit of a problem with the spherical theory, if stuff is ejected (or diffuses out) at low speed it would still have the orbital velocity of the comet superimposed, so it should be ellipsoidal/sausage shaped, elongated fore and aft, but with a circular crossection a...

I am wondering why it appears so symmetrical, circular even (although spaceweather.com calls it spherical, dunno how they know that in 3d !? ) I have read of various possibilities such as impact/collision and collapsing sink-holes/caverns but would that not require the coincidence of 'it' happening...

the bloody thing hit something. Bet you a an ice cold one. rare collisions does not imply no collisions. :P I don't know how to collect on that bet! But if hitting something at all is rare, doing so twice in a century is truly unlikely. And there are perfectly reasonable mechanisms that can explain...

I know this is a long-shot, but is there any possibility that it increased in brightness due to a collision? Given that it orbits in the asteroid belt, surely this is a possibility? Of course it is possible, but I think in this case very unlikely. Collisions are rare in any case (even in the astero...

Among other things, you can see just how much is now known about the variation in appearance of stars (at least wrt starspots), for a significant subset of stars, even though there are direct, visual waveband, images of only a tiny number of stars ... I've recorded starspots for dozens of fast rota...

Not even the LMC or SMC? Not even close. The Hubble is capable of a resolution of a bit better than 0.1 arcsec; larger ground-based telescopes using adaptive optics can do a little better than that. But that resolution, impressive as it is, only allows a few of the very closest, largest stars to be...

This nebula, like others I have seen here, has light emanating from the fringes of the dust-gas cloud. I have assumed that that light comes from stars that are hidden by the nebula but their light shines at the edges of the cloud. My question is, can light be emitted from a celestial body that has ...

I believe that Betelgeuse is appriximately the same diameter as Jupiter's orbit. If we were capable of imaging its surface with any clarity, we should also then be able to resolve Jupiter sized planets in jupiter sized orbits around closer "sun sized" stars. It's still very difficult. 2M1...

It's amazing that we've never actually seen a star other than our own Sun. That depends what you mean by "see". We have learned vast amounts about other stars by studying their light. However, I assume you mean "resolve"? In fact, a few stars have been resolved telescopically, a...