Starship Asterisk*

As far as I know, SN1987A in the Large Magellanic Cloud is the closest observed supernova since Kepler's supernova of 1604.

So I'm wrong about gravity crossing space at the speed of light? What is the physical nature of the information in gravity that does cross at the speed of light? Changes in the gravity field propagate at speed c . However, in your scenario, where the entire Universe is created at some t=0, insistin...

There are some technical problems with making your model work. The equations of the general theory of relativity not only governs how spacetime evolves after you've started it; they also constrain which possible shapes a single instant-slice of spacetime can have, given what's in it. And, as far as ...

I've also wondered about the fact that we find ourselves inside a spiral galaxy, given the seeming abundance of elliptical galaxies out there. Are they really abundant? I was sure I knew most galaxies were elliptical, too, but just the other day I found this: Elliptical galaxies are believed to mak...

I was just looking at an animation of Saturn; it reminded me of an old question I've had since I was a little girl, 45 yrs ago. Why are so many orbits flat discs? Why isn't Saturn within a bubble of snowballs, rather than rings? Why do planets orbit Sol in a relatively disc shaped order? There are ...

I do not have a mind trained in mathematics, physics or geometry, so conceptualizing this is difficult for me. I heard, don't know where, that the universe is something like a Mobeus strip, turning back on itself, and that we are on the surface. A Möbius strip is probably a step weirder than you ne...

The man added that he had come to believe that nutrients in the soil weren't very important for the health of trees. "Access to plenty of water and daylight is what matters," he told me. As long as there are enough nutrients in the soil, even more of them are not going to cause greater gr...

No one needs to fertilize for sawgrass or switchgrass. 2) Replenishment of nutrients & organic matter can be accomplished by regular crop rotation with some green manure crop like clover or vetch which will be plowed under. Sawgrass and switchgrass certainly do need nutrients to grow. They can ...

I follow the APOD RSS feed (http://apod.nasa.gov/apod.rss) and in normal use every day i see the new APOD, but i also see yesterday's APOD appear in the feed again. ... Anyone else have this problem? It's even worse if you use Google Reader. There I only ever see yesterday's picture. Apparently it ...

APOD Robot wrote:On September 21st (Universal Time) Jupiter will be at opposition,

Precision is a good thing. We wouldn't want anyone to misunderstand it, so they went out and looked up on September 21st CEST, for example. They might miss it.

Chris Peterson wrote:It isn't certain that black holes are described by the Kerr-Newman metric.

I thought the point of the "no-hair theorem" was that they would have to be? But I've only seen popular accounts of that theorem, so it is possible that it has assumptions that are doubtable.

If my calculations above are correct (somebody please check them!), I was a bit confused what solar wavelength range you were integrating over, Oh, the entire spectrum. That's a bit lazy (it's what it was quickest to find a figure for), but I figured that whatever filter the hypothetical alien astr...

Maybe that's the Moon? There are stars to the left of it. Doesn't the full Moon come up just before the sun goes down? Yes (or just after), but not while the sun is still as high in the sky as the shadows on the sails indicate. Once the moon rises the 5-or-so degrees above the horizon it is shown a...

The Universe is flat (thanks to inflation) but it can still (topologically) be a "cylinder." What if the Universe is a long cylinder with the fine structure constant slowly varying along the length of the cylinder. I don't see how inflation could change the global topology of the universe...

Optical SETI supporters have conducted paper studies of the effectiveness of using contemporary high-energy lasers and a ten-meter focus mirror as an interstellar beacon. The analysis shows that an infrared pulse from a laser, focused into a narrow beam by such a mirror, would appear thousands of t...

are you sure that some alien scientist is not right now painfully yelling about some stupid people on this distant plant burning his eyes with a laser. Quite sure. The laser outputs 17 W at 589 nm. Even ignoring the atmosphere, the beam will not stay exactly parallel to the stars, but will diffract...

beyond wrote:AH, so the 'suck' factor is just the result of a really strong gravity caused by all the mass that has been sucked up?

Black holes do not suck! Or at least, do not "suck" any more (or any differently) than the same amount of mass in any other form would do.

Question: Why do artists always seem to depict a black hole as being below the plane of the incoming material? Is it a misunderstanding of the gravity well? I don't think it's "always". But in those cases where they do, your hypothesis is probably as good as any. In this APOD I'm more con...

Amir wrote:What happens when Light or Matter Arrives at the edge of the universe?

The universe has no edge.

In the real world, a black hole pretty much always has an additional attribute: an accretion disk. That's a rather bold claim. The ones we know of have one, because otherwise they'd be invisible, and we wouldn't know they were there. But is there any reason to think a black hole must be able to mai...

At the risk of sounding a bit dumb, are you saying that a charged particle can not transmit information at all, or just not when IT is going faster than c ? No. He's saying that light sometimes goes slower than c. Light in the atmosphere is one such example. It travels very slightly slower than c. ...

Look up 2012, Mayan doomsday prophecy. This is supposed to be when the Sun goes back up across the galactic plane. It is all over the history channel shows. Again, who does that supposing? Wild-eyed crackpots, mostly. Followed by a flock of media people who don't care whether what they say is true ...

On average: 1) the stars in our stellar neighborhood should be moving perpendicular to the galactic-center radial 2) and the sun is moving just ~20 km/s relative to them so the earth is moving within 5º of the perpendicular to the galactic-center radial http://en.wikipedia.org/wiki/Sun However, the...

On Dec,21, 2012 the sun is supposed to cross the galactic equator. And thus, Doomsday! Supposed by whom? Certainly not by anyone with the least bit real knowledge of astronomy. The IAU defines a "galactic coordinate system", according to which the galactic equatorial plane by definition p...

bystander wrote:

Ann wrote:skiftnyckel?

Wrench in general, or an adjustable spanner (crescent wrench) in particular?

Skift means something like "change", so definitely adjustable. Amusingly, in Danish this is known as a svensknøgle: "Swedish wrench".