Monday, November 19, 2012

Not the Genie you want to dream of

A belated response to this video which did the rounds back in July, starting here it seems. I actually composed most of this IN July, but never got around to posting it until now.

The main reaction seems to have been "ZOMG they're standing under an A-bomb! That's CRAZY!".

I've had an odd interest in nuclear weapons and warfare since childhood (by-product of being terrified by them in the 80's), and from that perspective, there's crazy, and then there's crazy.

While it looks (and well, is to an extent) crazy, it isn't as crazy as it looks. For my money it definitely isn't as crazy as say advancing through ground zero, atomic interperative dance, or guys walking around with nuclear bombs on their backs, or even a nuclear powered aircraft (what could possibly go wrong?!).

The Bad Astronomer gives a good explanation of the technical aspects of why it wasn't so dangerous as it looked here, but the short version is it was a little bomb and they were a long way away from it due to the detonation altitude. How little? A teeny 1.5 kilotons, equivalent to 1500 tons of TNT (the NPR blog figure of 2kt is wrong, among other detail errors). There have been bigger man-made explosions that were non-nuclear. Thanks to the curious but slightly creepy Nukemap app, this can be represented graphically using the effects on poor old yardstick-of-doom Hiroshima. The effects of the 1945 bomb are here, and the bomb in the video here. See? Tiny.

As an aside, just for comparison/perspective this is what would have happened had Hiroshima been bombed using the strategies and weapons of the early 60's (sliiight overkill), and what a medium size strategic warhead would do to the place now (you need to adjust the scale a bit). Not so tiny.

So that's one bit of crazy. Another is that this was an era when nuclear weapons were openly tested above ground, by the dozens around the world. There are some who would argue that perhaps we should go back to the occasional above-ground demonstration, just to remind the powers that be what they are dealing with (many of those who witnessed tests maintained it was the only way to truly appreciate the power involved).

Another bit of crazy involves the reason for the test itself. It was for a defensive weapon (ponder for a minute the sort of situation where using nuclear weapons over your own territory becomes not only acceptable, but a good idea. . . ). In an era when accurate guided air-to-air missiles were in their infancy, someone reasoned there would be more return with a bigger bang. The weapon that resulted was the AIR-2 Genie, basically an unguided atomic skyrocket that would go off a certain amount of time after launch, hopefully somewhere near its intended target. US and Canadian interceptor aircraft would carry one or two of these should the need ever arise to knock incoming bombers out of the sky as quickly as possible (the Genie wasn't the only weapon built to this philosophy; defensive nuclear armed surface to air missiles were developed and deployed by both East and West in the Cold War).

Part of the reasoning behind placing the volunteers at ground zero was to demonstrate it was safe to use over friendly places, since inadvertently nuking your own cities in the process of preventing others from nuking them isn't that great a defensive strategy. You also want to keep the interceptor crews actually launching the thing alive as well though, which places another limit on the warhead size. While it's easy to think such a weapon might have been quickly rendered obsolete (perhaps by something that could actually be guided rather than aimed) and remained in the 50's and 60's, it actually stayed in frontline service until the mid 80's.

Wednesday, November 14, 2012

Partially eclipsed

 Image credit NASA, Nov 14 NZ Time, click to enlarge

The partial eclipse today was AWESOME. We didn't get treated to the full total thing like Cairns, but even at 76% obscuration like we had in Wellington it was spectacular. Which is good, because it will be 2025 before we get another one here anything like it :).
 Image credit Stardome

The further south you went the less eclipse you got, but to make up for it we had a perfect day, the only clear sunny day I can remember seeing an eclipse on, and this was the best I've ever seen. As not quite totality approached, there was a distinct sudden chill in the air to go with the eerie not-quite-right light level for a bright sunny day. Being able to both see and feel the eclipse was amazing.

Since direct observation with the naked eye is not an option with these things (unless you want to risk permanent eye damage, can't stress that enough), indirect viewing was in order. Around the science establishment I work at there were a few methods being demonstrated.

My attempt at making a pinhole viewer using a piece of paper on a clipboard and a piece of cardboard was successful, but unspectacular (although still cool since it was my first glimpse of the eclipse):
A colleague made a more effective one (I think the key might have been a thinner piece of cardboard to act as a lens).
Failing that you could always just use your hand, making the "OK" sign and allowing the sunlight to pass through the gap between your thumb and forefinger.
Or just find a tree, where the gaps between the leaves can be just as effective as pinhole lenses,  a phenomenon I'd heard about but never seen before today:
Pinhole viewer using just a tree (evergreen preferred) and a piece of paper:
A slightly more elaborate setup involving bigger cardboard, a tripod and binoculars also yielded good results:
Nothing was quite as good though as (safely) looking right at the sun and moon through a suitable filter, in this case a handy piece of mylar film that another colleague had thoughtfully prepared:
And this was the icing on the day for me, since when I put the mylar in front of my telephoto camera lens the result was spectacular (disclaimer, be very, very careful when you do this. Never ever look at the sun directly through unfiltered optics like telescopes, binoculars or camera lenses). With the settings adjusted you could even see sunspots (the little dots) and mountain ranges silhouetted on the moon.

One of the coolest things I've ever seen, let alone been able to photograph