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Comment: Re:1960s??!! You are so funny (Score 1) 140

by mbone (#47774113) Attached to: Underground Experiment Confirms Fusion Powers the Sun

Good god man, Hans Bethe worked out the fusion processes in the Sun in the late 1930s.

http://en.wikipedia.org/wiki/B...

Yes, but there was no direct observational evidence of it until the Homestake neutrino experiment in the 1960's. Theory is nice, but in physics the experiment's the thing. (And, when the Homestake experiment came up 66% short, there was no shortage of people claiming that Bethe was wrong in one way or another.)

Comment: Re:That's not how science works (Score 1) 140

by mbone (#47774079) Attached to: Underground Experiment Confirms Fusion Powers the Sun

It is in my experience rare to meet a physicist who cares much about mathematical rigor, or who uses proofs in their work. Occasionally it is important (e.g., in some "no-go" theorems), but I feel certain that most physicists would object to saying that "Mathematical proof is central to much of physics." It is in fact notorious that much of existing physics was done and completed before anything like mathematical rigor (and, thus, proof) was brought to the subject at hand, nor did the achievement of rigor actually change anything much in the physics.

An excellent, and familiar, example, is the Dirac delta function, where it took years before the mathematicians were convinced that such a thing could possibly make sense. Even today, vastly more physics students are taught about Brownian motion than the Ito statistical calculus...

Comment: It's all a matter of energy (Score 5, Informative) 140

by mbone (#47770059) Attached to: Underground Experiment Confirms Fusion Powers the Sun

It has been known since the 1960's that the Sun produces energy from fusion, but the actual neutrino's observed then (and until now) were high energy electron neutrinos that actually came from relatively unimportant fusion chains (from the standpoint of energy production), not the proton-proton chain though to produce most of the Sun's energy. Since there was a "neutrino problem" (the Sun appeared to produce only 1/3 of the neutrinos predicted by theory), some people did think that for whatever reason the main energy source - the proton–proton chain reaction - was for some reason mostly shut down, presumably as part of some long period oscillation in the Sun's deep interior (although Arthur C Clarke wrote a novel, "The Songs of Distant Earth," in which it was a permanent shutdown of the Sun's fusion, and a prelude to our Sun going supernova). At that time, the inability to directly see the pp chain seemed like a big deal, but since the discovery of neutrino oscillations (which nicely explain the factor of 1/3), and also with solar interior modeling from helioseismology, there has been a pretty solid consensus that the pp chain was running the Sun, even if there was no direct observation of it.

Now it has been proved. In 1990 that would have been a big deal, but now it is more a matter of just being satisfyingly complete in our observations of the Sun.

Comment: Put you money in the mount (Score 3, Interesting) 185

by mbone (#47739287) Attached to: Slashdot Asks: Cheap But Reasonable Telescopes for Kids?

Get the best (Ha-Dec) mount you can. (I would not get an Alt-Az mount for a beginner on a budget.) Most department store type scopes have adequate optics, but very crappy mounts, and that makes for a miserable viewing experience. Get a very sturdy mount with a cheap scope,and then if the kid wants to move up, they have the mount for it.

Comment: Re:Is it too late? (Score 1) 139

by mbone (#47738679) Attached to: 2 Galileo Satellites Launched To Wrong Orbit

Most major GPS chip sets now actively filter pulsar noise.

Got a link for that? I know that most pulsar observers filter out GPS and other satnavs (GLONASS sidebands are especially annoying) but I have not heard of GPS receivers having pulsar ephemerides.

 

The thing about pulsars is they are better clocks than what is being launched and they transmit on all frequencies. The ephemeris calculations are much harder but it has be used to 2 meter accuracy and it isn't even limited to working just around earth. I wonder why they spent so much money to duplicate two existing systems that weren't even state of the art when they started. Maybe it was because you can't license pulsar transmissions.

Or maybe because observing pulsars requires a substantially bigger antenna than a hand-held smart-phone - 170 m^2 (and 500 Watts!) for a phased-array radio dipole and 0.1 m^2 for an X-ray Pulsar Nav system in Becker et al. (and the latter could only be used in space, outside the Earth's atmosphere).

Comment: Re:ugh (Score 1) 139

by mbone (#47738551) Attached to: 2 Galileo Satellites Launched To Wrong Orbit

The Fregat has a reputation as being an incredibly reliable and accurate upper stage - I have heard of on-orbit accuracies on the order of 100 meters - and there were no initial reports of upper stage technical problems (such as a premature shutdown). That tells me that this is likely to be either a communications problem, or a simple screwup.

Comment: Re:Stupid metric system (Score 1) 139

by mbone (#47738491) Attached to: 2 Galileo Satellites Launched To Wrong Orbit

Not quite - it's more that there were a number of different units for different purposes and different locations - inches and feet and rods and yards and chains and furlongs and fathoms, etc. (and these are just for length - there are acres and oxgangs and virgates etc. for area, and on and on). Over time, some of these dropped out and the others got rationalized, leading to a bunch of different ratios.

At least some of the duodecimal units (and I believe all of the base 360 units, such as degrees) are straight from the Babylonians.

Comment: What a debacle (Score 5, Interesting) 139

by mbone (#47736417) Attached to: 2 Galileo Satellites Launched To Wrong Orbit

This will for sure mess up the constellation, which is designed to minimize the times where some places on Earth do not have 4 satellites above the horizon, and also the places where this is going to happen (i.e., coverage gaps over the far South Pacific are likely to be more acceptable than over Northern Europe) . Since these satellites are too low, they will have shorter periods and will thus not be commensurable with the existing constellation, and will drift in and out of place.

You can be sure ESA engineers are busily looking at orbits this weekend, to see what can be salvaged from this debacle. Now, they may be really lucky, and have gotten an orbit where these two satellites can be used to fill a hole in the current constellation. I would bet in that case that both satellites would serve to fill the spots normally filled by one satellite; so at best only one, but if (as is more likely) they are unlucky, two satellites will have to be launched to fill the gaps.

In other words, while these satellites are not a loss, and will be used, new launches are likely to be necessary to make the constellation whole, which will cost as much as if they were lost.

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