Starship Asterisk*

gmurray618 wrote:Can anyone explain why the upper part of Saturn is illustrated? My bets guess is reflected light from the rings. Is this correct?

APOD Robot wrote:Saturn itself [is] faintly lit by sunlight first reflected from the rings.

ceelias wrote:The accompanying text calls the rings "surprisingly thin". How thick (thin) are the rings?

According to Wikipedia the rings' thickness ranges from ten meters to one kilometre.

What does the equation look like, so to speak, that surmises Dawn will orbit Ceres for millions of years? Is that accurate and realistic to arrive at that determination? Just wondering... Newton's equation of motion and his law of gravitation. Given proper initial conditions (position and velocity)...

Another interesting feature of note in this photograph--It shows stars! At first I was puzzled, because daytime photos of Earth from ISS never show stars. Then I realized that this is not a daylight photo. (It is amazing how much it looks like one.) The exposure they used to make the auroral light ...

However, diffraction is always a wave phenomenon. It does not occur with rays or classical particles. No. Experimentally, diffraction occurs with particles (even a single particle) and can be treated by QM in both the wave and particle domain. Chris, now you confused me. To clarify, I talked about ...

Happy birthday! And thank you for bringing an APOD to us every day for 20 years.

And refraction is not a quantum effect, while diffraction is? No. Whether a phenomenon needs to be described by classical physics or QM depends on the scales of the problem. One such quantity is the de Broglie wavelength of the system. If the spatial extend of the system is comparable to it's de Br...

I did some searching and found this helpful article about lunar coronae by Les Cowley et al. . Here I give a brief summary: A lunar corona results from diffraction of moon light off water droplets. It is different from a rainbow in that the latter results from reflection, refraction, and dispersion ...

[...] Not everything is a quantum effect. But diffraction is. Diffraction is only fully understood by utilizing QM. Classical theory is only an approximation. It's a very good approximation in many cases (but not so good in the case of diffraction by small particles), but an approximation all the s...

Hi, can someone please explain to me (or just post a link) why this is a quantum effect? I am used to thinking of diffraction of light as something that can be explained using classical wave physics in the Fraunhofer regime (i.e. Airy disks and all that) and so I don't see the quantum nature here. ...

Just heard in the news that Philae has woken up.

Saturn appears to be oblong. Is this because we see its rings?

The drawing by Escherr reminds of a talk from one member of the Rosetta team. Since the comet is irregular shaped defining an equator etc. is non-trivial. Here is a map of the comet they came up with.

Chris Peterson wrote:Or not so fittingly named. It always brings the other end to mind for me.

Thanks, Chris! Now, how do I get this image out of my mind?

Although a liquid at room temperature Mercury (Hg) has an atomic wt. of 80 vs. Gold (Au) at 79 The atomic numbers of gold and mercury are 79 and 80, respectively, and are the number of protons inside the nucleus. The atomic weights are ~197u and ~201u, respectively, with 1 u being 1/12 of the mass ...

Thanks, all. I have a chemist friend who I keep forwarding articles to, asking if they're real or hyped. They're almost never not hype! Guess it's the same for astro-physics articles.... You could go through almost any article and cross out any words like "surprising" and "baffled&qu...

One main point that does seem relevant is that chemists continued to use the term atoms when describing matter. While I was off yesterday, I was re-viewing Sean Carroll's "Beyond the Higgs Boson" which he was reiterating the fact atoms really don't exist. They are only the result of stron...

APOD Robot wrote:As friendly as cows may be [...]

Believe it or not, but people have been killed by cows (in German). I haven't heard of something like this of goats, giving them another advantage over cows in space.

Solar System ephemerides are established by at least three different methods. Some are based on empirically derived series solutions, some are based on precise observations, and some are based on numerical simulation. These are regularly checked against each other. I don't see how the simulated sol...

... The time dependent gravitational field of a accelerating mass ... What exactly are you referring to here? Stars orbit the center of the galaxy in more-or-less elliptical orbits, hence they are constantly accelerated. And since the size of a galaxy extends over 100 light years, I wonder if one s...

When our Earthly view of a galaxy is at an oblique angle, is it true that we're seeing the far edge as it was tens of thousands of years before the light we're getting from the near edge ? Easy to think we're looking at the entire galaxy as it was 50 million years ago, but is there a temporal gradi...

I find it remarkable that we extended the scale of our knowledge since then. On the large scale the movie stops at 100 Mly, whereas today we have observations of the entire observable universe . On the small scale the movie ends with the speculation of the existence of quarks, the which is now fact .

Gravity wave interferometers are built to detect tiny distance changes between mirrors. Is this because it would take light more time to travel between them if the distance increases, or because the total number of wavelengths of light between them would change, with a passing gravity wave? I ask b...

I don't have access to the nature article, but judging form the abstract, it does not sound very new, indeed. Here is another paper on Bounds on length scales of classical spacetime foam models (free online here).

Thanks for bringing this up, geck. I am currently in the UK and might have a chance of experiencing a partial eclipse. My cousin trying to organise some goggles, but the demand is rather high at the moment. In case he can't get some, is there some way to improvise a filter?