# Tag Info

38

Barring whatever fantastic energies would be required to stop the mass of the Earth from rotating and then changing the direction of the rotation, one of the major things I can see changing would be the expectations of weather patterns. Part of what affects our weather is known as the Coriolis Effect. While there would certainly be effects from the ...

33

Briefly: Because the moon's orbit "wobbles" up and down, so it isn't always in the plane of the earth's orbit around the sun. There's a 2D plane you can form from the ellipse of the earth's orbit and the sun. This plane is known as the ecliptic. The moon's orbit is not exactly in the ecliptic at all times; see this (slightly overcomplicated) picture from ...

29

The highest resolution 3d printers I know of are around 1600dpi, which is a resolution of about 15$\mu m$. Telescope mirrors have to be smooth to fractions of a wavelength of light, so the resolution of current printers is nowhere near good enough. Whether 3D printers could one day be good enough is a different question, but given that the improvement in ...

28

Not quite like in the photo above, which shows more than what the naked eye can see, but yes, absolutely! Our galaxy (well, the chunk of it visible from these parts) is a naked-eye object. The fact that your question even exists shows how much time is now spent by people under light-polluted skies. It will not be visible from the city, however. You need to ...

27

I stumbled across this question, and while it is an old question and there are some halfway decent answers, I think it deserves a more in-depth response. I completely understand the question, which I think is am excellent question. Trying to understand the phases of the moon is much more difficult than most think. The short answer of it is that you cannot ...

26

Money and willpower. With any program (scientific, military, public works, etc.) it all depends on the amount of money someone is willing to put to it, and how much backing and protection that program has from getting money re-prioritized to other projects. You are making a false dichotomy of attempting to present our past actions as a justification for ...

24

The estimates I've read are similar to yours: 200 to 400 billion stars. Counting the stars in the galaxy is inherently difficult because, well, we can't see all of them. We don't really count the stars, though. That would take ages: instead we measure the orbit of the stars we can see. By doing this, we find the angular velocity of the stars and can ...

23

First of all, the universe is most certainly not shaped like an hourglass. It simply looks that way because the gas and dust in the plane of our galaxy obstruct our view of anything outside the galaxy in those directions. So we can only see other galaxies (and similarly distant objects) by pointing telescopes at some angle to the galactic plane. That gives ...

23

A typical giant galaxy, such as the one you've provided a picture of, has a radius of something like $10\;\rm kpc$ (kiloparsec - $1\;\rm pc \approx 3.2\;ly$). A supermassive black hole hosted in such a galaxy has a mass of something like $10^6-10^9\;\rm M_\odot$ (solar mass, $1\;\rm M_\odot \approx 2\times10^{30}\; kg$). The monstrous billion solar mass ...

23

One cannot tell by the light spectra. Hydrogen and antihydrogen would give the same lines in the spectrum. The prevalence of matter over antimatter from other evidence indicates matter is predominant in the observable universe, and here is a nice review. How do we really know that the universe is not matter-antimatter symmetric? The Moon: Neil ...

22

I have operated public observing nights at various universities for eight or ten years. These are the objects that have stood out for me. Saturn and Jupiter are the "stars" of the night sky. Bar none. Spec. Tac. U. Lar. If you can look at Saturn with nothing between it and your eye besides a few panes of glass, and see it hanging in the sky in all its ...

22

There are a variety of methods used to measure distance, each one building on the one before and forming a cosmic distance ladder. The first, which is actually only usable inside the solar system, is basic Radar and LIDAR. LIDAR is really only used to measure distance to the moon. This is done by flashing a bright laser through a big telescope (such as ...

22

First, the speed of other galaxies isn't too helpful. For example, the radial velocity of the Andromeda galaxy relatively to us is 300 km/s, i.e. 0.1% of the speed of light only. Moreover, internally, everything in that galaxy moves by pretty much the same speed and is confined to the vicinity of that galaxy which makes us pretty sure that no piece will ...

21

The moon does have a night and a day, but this isn't as fully connected to your question as you might think. The moon is tidally locked with the earth, meaning that the same side always faces earth. Since the moon also orbits around the earth (with a period of a lunar month), this means each side changes, over the course of a lunar month, between facing ...

20

Why don't we observe any relativistic asteroids? The answer to this question would not be complete without mentioning the virial theorem. Considering our galaxy as a system of $N$ gravitating objects, according to the virial theorem, twice the average total kinetic energy of all objects, plus the average total potential energy of these objects, adds up ...

20

Mauna Loa is an active volcano. The last eruption was in 1984.

20

Those code names all come from certain catalog. For example, NGC means 'New General Catalogue'. There are various catalogs aiming at different objects, like stars, nebulae, galaxies, etc, but not for the Earth, at least not yet. You can find almost all known astronomical catalogs and tables at CDS

19

Depending on your definition of "object," Neptune is currently the farthest. It was visited by Voyager 2 in 1989. New Horizons will be visiting Pluto in 2015 If by object you mean cosmic structure though, then Voyager 1 is currently in the Heliosheath and is expected to reach the heliopause by 2015. These are regions that describe interactions between the ...

19

Using the distance between the Sun and the Earth, at least for distances within the Solar system, just gives a better feel for the scales involved. You can't really imagine a distance of, say, 1000000000 kilometers -- or at least I can't. (I deliberately didn't include commas in that number, to illustrate the point.) But using a concrete physical distance ...

19

I suspect the question may be unanswerable, and possibly even meaningless. As I understand it, the giant impact that resulted in the formation of the Moon would almost certainly have also completely liquefied whatever crust the Earth had at the time, producing a global "magma ocean". Thus, there would've been no traces of the impact left — or rather, ...

19

The day/night cycle is the first obvious effect: Days and nights would both be longer (EDIT Or shorter, apparently I got it backwards) if the speed of rotation is the same. All life on the surface of the planet has evolved for day/night cycles of roughly the length we experience now, with leeway for the difference between summer and winter. A sudden ...

19

It's spherical because the main dish cannot be steered; steering is done by moving the receiver (the big thing hanging over the center of the reflector). A parabolic reflector would produce varying errors when aimed in different directions; a spherical reflector has the same error for all directions. Presumably the receiver is designed to compensate for ...

19

Wikipedia's page about gas giants says so. The paper where the computations are done is arXiv:0707.2895. I haven't read the paper in detail, but the figure you are interested in is figure 4 (p21), where you can see that the maximal size for a planet is roughly 1.5 Jupiter radius, for a planet made of 2000 $M_\oplus$ if hydrogen. Beyond this mass, the ...

18

Good question! As you guessed, nothing can escape from a black hole, so it is impossible to see one directly. (Quantum field theory does predict that black holes give off an extremely tiny amount of thermal radiation, but it's so little that it we can't detect it from Earth.) Scientists assume that black holes exist based mainly on the predictions of ...

18

The reason being closer to a heat source makes you warmer is the inverse square law. Think of it this way: If you have a $1~\mathrm{m}^2$ piece of material facing the Sun and located at Mercury's orbit, it will be quite hot. What does the shadow of this square look like at Earth's orbit (about $2.5$ times further away than Mercury)? Well, it will be $2.5$ ...

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