PakledHostage

I've tried to fix position by using several shadow length measurements obtained around noon time and plotted against time. The shadow length and time of the resulting curve's lowest point can then be used to calculate latitude and longitude. As I mentioned in my earlier post, the resulting fix isn't very accurate though. With a sextant on the other hand, each measurement yeilds a line of position. (It is actually a circle on the Earth's surface, but it looks like a line on the scale of most charts for all but the highest objects in the sky.) Take measurements of two different objects and you get two lines of position. Where the two lines of position cross is where you are located. And while the two lines actually cross at two locations, the second will usually be off the chart. It is also possible to shoot the same object (like the Sun) twice to get two lines of position, but you need to wait at least an hour or two between shots. Then if you're moving during that time, you have to offset one or the other of those lines of position based on your ded reckoning. This is called a running fix. Adding a third shot for a third line of position yeilds a triangle near your true position. It is traditional to plot the centre of that triangle as your celestial fix. It is possible to calculate a position within a few miles of your actual position using these methids, and you don't need to wait for a noon day sight to do it. You just need more complex math.

Then we'll have to agree to disagree.

I didn't intend any disrespect. I was only pointing out that the video's script was obviously biased in favor of the "Pluto is a planet" camp. There was no mention of Dawn's mission to two other dwarf planets (Ceres and Vesta) other than as an afterthought in the credits, and it pretty clearly stated that next month's flyby is the end of the first era of planetary exploration. I just thought that was interesting, given that there is still a contingent out there that is upset about the IAU's decision to demote Pluto. I am looking forward to next month's flyby just as much as everyone else, regardless of how Pluto is classified.

You're right that this debate is getting tiring, but I'm not sure your post puts a lid on it. As you say, we'd all get used to it if the whole world suddenly switched to some arbitrary system. But that's just it: The whole world switching to that arbitrary system would standardize measurements around the globe. As it is, the Metric system is used in 95% of the world, while the last hold-out has enough economic power that its stubbornness affects everyone else. It would seem to be the path of least resistance for the US to finally switch too, but that doesn't seem to be likely any time soon. And even if it was, there would be significant hurdles to overcome. That doesn't mean it is impossible though. Both Canada and Australia switched over in the 70's. Most of the Canadian prairie are still divided up into 1 mile by 1 mile sections and that isn't ever going to change, but the country survived the transition. On a per-capita basis, it probably wasn't any cheaper for Australia and Canada to make the change than it would be for the USA to do it, given their vast areas and relatively small populations. But you're right. You can come up with a million and one reasons not to get started, so we all may as well just suck it up and live it.

I didn't realize it was that much higher, but it makes sense when you think about it. Thanks for the correction.

True, but it wasn't when they made the video.

You'd have a tough time achieving any sort of meaningful accuracy. Remember that one degree of error in latitude is roughly 100 km. You'll have a hard time measuring anything to within a degree. And even if you're lost in the wilderness, you probably know your position within plus/minus 100 km anyway. By comparison, my sextant's worm gear and vernier allows measurements to within 1/600th of a degree (0.1 minutes). In practice, that type of accuracy isn't practical. Waves on the horizon and atmospheric refraction introduce larger errors than that. Errors due to height of the eye above the ocean surface (dip) are also significant, as are errors in time as small as 4 or 5 seconds. By carefully judging the location of the true horizon between the waves, compensating for atmospheric refraction and dip using lookup tables and accounting for known drift rates in my chronometer, I can fix a position within a few nautical miles of my GPS position, but it takes careful attention to detail. That's close enough to find the lights, but it also puts the achievements of guys like Frank Worsley into perspective. If you don't have a good horizon due to fog, haze or some other obstruction, you can use a tray of water as an artificial horizon, but you need to have previously measured how far below the true horizon your pan of water is, for some fixed relative position. It won't work on a moving boat though. You can also use a special scope on your sextant that has a built-in bubble level. Aircraft sextants have these because it is almost impossible to see a sharp horizon from up high.

I don't know... They don't seem to have been able to get over the fact that Pluto isn't a planet anymore.

I think you are confusing sapience and sentience... Sapience does allow you to control your body to an extent. Control of mind over body is central to a lot of sports like climbing, martial arts and even endurance sports like cycling and running. Persevering in the face of hunger, fear, thirst, pain etc are critical to doing well in those activities or even being able to do them at all.

There's a bit of a discission about ablative heat shield materials on the Atmospheric Entry wikipedia article. I was familiar with the Phenolic impregnated carbon ablator (PICA) that was used on Mars Science Lab and Stardust's heat shields, but I wasn't familiar with the SLA-561V ablative compound used on earlier Mars landers. Both MSL and Stardust's atmospheric entries were particularly demanding. Stardust because it was the highest speed entry ever and MSL because it was a direct entry from a hyperbolic trajectory by a massive lander. And even though an entry like MSLs into Mars' atmosphere was at lower speed than typical Earth atmospheric entry from LEO, I have read that Mars' carbon dioxide atmosphere reflects heat back to the heat shield during entry, rather than allowing it to cool by radiative heat transfer.

No, Kelvin is one of only seven SI base units. SI does not have any other base units. All other metric units are defined in terms of these seven: metre for length kilogram for mass second for time Ampere for electric current Kelvin for temperature candela for luminous intensity mole for the amount of substance. Notice that neither the nautical mile nor degrees Celsius are included in the list.

You can also find more information here.

I did read something once in a Douglas Adams book about a bowl of petunias having a thought... Does that count?

Erm? Kelvin IS an SI base unit just like the metre, second, etc. There are 100 K between the temperature at which ice melts and water boils, just as there are 100°C between the temperature at which ice melts and water boils (at standard sea level atmospheric conditions). The imperial equivalent to the Kelvin scale is the Rankine scale.

Here's the TED video for anyone who hasn't seen it: Also, does anyone have any updates? One report that I read earlier today said that data links between Rosetta and Philae were possible every 12 hours and 30 minutes. There should have been at least two windows by now since the first one. Are they getting more data or has Philae stopped transmitting again?

It operated for about 60 hours after it landed last November, so it was certainly in serviceable condition after it landed. They did what science they could back then before the batteries ran down and then they put it into hibernation in the hopes that this day would come. With this morning's news, Philae is transmitting, the batteries are now warm enough again that they can be recharged and the solar panels are generating 24 Watts or so. Things are looking up. With careful management and a bit of luck, they'll be able to pick up where they left off last fall.

The issue of decimal time, lat/lon degrees - minutes - seconds and the number of degrees in a circle are all straw men. The point of encouraging the US to switch over to metric is that it would standardize measurements across the world. The rest of the world could just as well switch to imperial, but nobody is (quite rightly) pushing for that. Metric was developed to be based on only a handful of reference units rather than a hodge podge of units that developed organically over centuries. This makes standardizing measurements around the world (and indeed anywhere else we may travel) simpler because most of those base units are defined in terms of physical properties that are invariant and can be established anywhere independently.

I'd always hoped this day would come! This is almost more exciting than the original landing. Congratulations ESA for sucussfully sheparding Philae through the past few months and for building such a robust probe in the first place!

I'll just leave this here: http://forum.kerbalspaceprogram.com/threads/116406-The-Martian-by-Andy-Weir?p=2005773&viewfull=1#post2005773

And it isn't unique to America either. Our government in Canada has muzzled all scientists who are federally funded. They aren't allowed to speak to the media without first having their responses vetted by the party to ensure they don't contradict party ideology. Science Under Seige - Part 1 Science Under Seige - Part 2 Science Under Seige - Part 3

Thanks for posting that. I watched it on my TV this evening via Chromecast. (You know you're a nerd when you crack open a bottle of beer on Friday night and watch a documentary about New Horizons...)

I agree. I haven't yet read the book but I will pick it up the next time I go by a library or book store (I am old enough that I prefer my books "analog"). I am hopeful that the movie will be faithful to what is by all accounts a great story. If they do at least as good a job at staying faithful to the plot (within the restrictions of a screenplay) as they did with Ender's game, it will probably be brilliant. Orson Scott Card was heavily involved in the production of Ender's Game and it showed. Hopefully Andy Weir's involvement in the production of The Martian will pay similar dividends.

Just for the record, some of us who thought that Interstellar and Gravity sucked had no problem with the "science" or the special effects. There was plenty in the cringe inducing plots to turn many people off those movies. It was as if the writers were trying to pack too much in - to hook as many people as possible with emotionally affecting scenes. They ended up coming across as contrived and clichéd instead. I honestly felt like I was being manipulated. Sometimes you have to look past any inaccuracies in the technical details and special effects that support a story. It is much harder to look past a story itself, when that story is badly flawed.

My car's speedometer and odometer are in km, yet my car still works on American roads. And if you can place a marker at a rather arbitrary 5km interval, why can't you place one at 1.6 km intervals? Heck, a lot of highway signs on the interstate in the western states already have both metric and imperial. It may be prohibitively expensive to change over all the signs and markers as a group replacement, but it can be done on an attrition basis for far less money. Why not get started? The journey of a thousand miles 1609 kilometers starts with a single step...

I think you guys both have a good point. The problem comes when it is taken to extremes. If it were up to me, movies would be judged on plot (hence my dislike of Gravity and Interstellar) rather than scientific accuracy and special effects, but I know that my position would also be unpopular if it were taken to extremes. A lot of Shakespeare's plays have great plots but I wouldn't waste my time going to see one... A movie version, sure, but not an actual play. I need some "special effects" just as I need some scientific accuracy to hold a story together.