Starship Asterisk*

G'day from the land of ozzz The Pleiades Star Cluster June 20, 1995 Its amazing to find that these stars formed at the same time. How could this be so? It is actually normal and expected. Groups of stars (sometimes quite large) form together, in regions where the conditions are right. Eventually, t...

It is fascinating to contimplate this... everything constantly moving... for a long time we thought the Earth was rock steady and everything else moved. Now we know better. Nothing is at a static state... and only 'nothing'. So how fast are we 'really' moving? (Relative to the Universe) Do we measu...

Do galaxies every just break apart and stop rotation? On any reasonable time scale we can deal with, galaxies are stable structures. They may be disrupted by a collision with another galaxy, but the resulting structure or structures eventually reconsolidate. Largely due to the conservation of angul...

Must be quite a sight for someone sitting on a parallel planet, orbiting a parallel sun in a similar location as us here but over there Probably not. All they would be likely to see would be something like a pair of Milky Way bands across their sky. It wouldn't be particularly bright or spectacular...

I’ve got a question that’s been puzzling me for a while. Current theory is that we are in an expanding universe and it will expand continuously forever or until the Big Rip. Dark energy, in addition to the initial momentum from the Bib Bang, is one of the phenomena that is pushing our galaxies apar...

I wonder if one added water (e.g., mined from underground or in the base of polar craters) whether it might harden and make a decent building material. Nope. The lunar regolith is an abrasive dust which is mainly basaltic, with many grains partly coated in glass. It might make a good component of s...

Now where on the topic. Do you think it might be possible to make a 3D image of our milkyway by making one foto in june and one foto in december of the same patch of sky and then superimposing them? Maybe a foto of Proxima century, because you have the best chance of it standing out from the backgr...

Is there any "real" (whatever the definition of real is) evidence of the existence of dimensions greater than the number that we as humans actually experience, or is all of this just the result of playing with mathematics? The idea that the Universe is four-dimensional in structure, calle...

That whole balloon theory is so overused. No, it is often misused . It provides an excellent analogy, ala Flatland , of the 3D appearance of a 4D universe. If our galaxies were all on a two-dimensional plane, aren't there 'sides' to the balloon? Because galaxies are not on a two-dimensional plane. ...

I know this is off topic, but I've been wondering this semi-subconsciously for a long time. Why is the term accretion used, instead of accumulation? Mainly history, I think. English is a very rich language, and there are often multiple words that could be chosen. In science, at least, once a certai...

The likelihood of two stars colliding is so extremely small. Okay, why? My guesses are: 1. Small cross-section to hit versus a lot of empty space. That's the primary reason. You could build a star gun, and shoot stars into galactic cores or globular clusters, and those stars will come out the other...

Is it possible for the event to have been caused by the direct collision of a larger star and a smaller star where the smaller star is obliterated and its mass can't be entirely absorbed by the gravity of the larger star? The likelihood of two stars colliding is so extremely small. I'd say that the...

What is the difference between this apparent explosion 165 years ago, and a nova or supernova? A nova is caused by the accretion of hydrogen from a companion star onto the surface of a white dwarf. When enough material builds up, it fuses, producing a sudden release of energy. Although material is ...

It does seem to make intuitive sense that the at the moment of the big bang some material was propelled first and therefore fastest... Ah, but intuition easily fails us when we start talking about cosmology. The problem is, no "material" was propelled outwards by the Big Bang. We tend to ...

My comment is more a question than an comment. Regarding the "red tinted debris" that is visible and "travelling fastest" of all. I have always wondered if such debris emited from the 'big bang' travelling fastest, and therefore furthest from the center, has not also cooled the ...

There is a reason NASA is not sending probes to Venus, at 90 times the Earth's atmospheric pressure and temperatures reaching 450 degrees C Venus is not a trip to Grandma's house either. Absolutely. Getting a probe to survive for any period of time on Venus is a much greater problem than it is on M...

My memory may be misled, but I recall Venus as having 600 mph winds, and for sure the atmosphere is so thick it can't be seen through. That thick atmosphere is precisely what makes getting to the surface easier. Actually landing required a degree of luck, since the earlier landers didn't really hav...

Considering the difficulties the Soviets faced in sending back pictures from Venus 30 years ago Phoenix was not much of an accomplishment .. almost like a walk to the corner store. Mars is an extremely difficult planet to land on- much more so than Venus. The combination of fairly high gravity and ...

Qev wrote:It's a bit of sloppy language, really. The parahelic arc always appears on the sky at the same 'height' from the horizon as the Sun.

"Altitude" is precisely the correct word, no sloppiness at all. However, "height from the horizon" is a little sloppy <g>.

Currently we don't know how heavy elements form Actually, we have a very good idea about mechanisms that produce heavy elements, and they are well supported by theory and observation. This issue with gold relates to another mechanism (in parallel with better understood mechanisms) that helps explai...

I don't agree irregulars are necessarily the result of mergers (SMC & LMC). Irregular galaxies may not "necessarily" result from mergers. That is simply the process that produces most of them. It's possible that there are other causes as well. The LMC, for instance, which is an irregu...

For my own interest in the APOD. The footnote says, since stars are so far apart, they don't collide during galactic interaction. Does this mean none collide, as an absolute? Surely this isn't right. Of so many, surely some must collide. No. Even at the core of a galaxy, the volume of empty space i...

I never click on the Digg links, and don't bother with the Digg site. It's a kind of social networking I'm not interested in. But it certainly doesn't bother me to visit sites that have Digg links- why should it? If it provides some value to you, as the APOD authors, great. It can be viewed as eithe...

How is the orientation of the photos decided? Many of the galaxies are "tilted", and would otherwise look very similar if the photos were rotated to lay them all flat. Most professional images are oriented north up, meaning that if you drew a line upwards, it would eventually hit the cele...

First of all, can anybody explain what this means? Preliminary indications are that the meteor stream is quite stable in time but variable in meteor abundance. Here's my interpretation: meteor streams vary in the stability of their orbits. That is, some streams are more influenced by gravitational ...