Saturday, April 18, 2015

Star Wars teaser far too tame

 The second biggest thing to hit the internet yesterday was the new Star Wars teaser. Like many, I clicked the link with interest.  But as a planetary scientist, I was disappointed from the first scene (via io9).

This is a wrecked star destroyer, half buried in desert sand.  The obvious implication is that the spacecraft has left space and crashed.  Is this realistic?  luckily, physics, and the internet, can answer this question.

According to this fan site a star destroyer weighs something on the order of 30-50 million metric tons. This makes it about 3000-5000 times larger that the meteorite which blew up over Chelyabinsk. If we assume the slowest possible re-entry, that from low orbit (about 8 km/s on Earth), then we can calculate what sort of impact this would have.  Better yet, we can use the internet to let the experts calculate it for us.

The Earth Impact Effects Program, by Marcus, Melosh, and Collins, simulates the effect of impactors of various sizes on Earth (our trusty stand-in for human-inhabitable worlds around the universe). Simplifying a star destroyer to a 1 km sphere with a density of 100 kg/m3 gives us the correct mass and a sensible size.  Falling from low Earth orbit, this object would need to dissipate 1.68 x 1018 Joules into the atmosphere or ground.  That’s about 400 megatons, or about 8 times more energy than the Tsar Bomba, the biggest nuclear weapon ever detonated.  Given a shallow impact angle, this object explodes in the atmosphere, raining small debris down onto the ground.

This, of course, is exactly what happened when real spacecraft suffered uncontrolled or malfunctioning re-entry: Skylab and the space shuttle Columbia (at ~70 tons, almost a million times smaller than a Star Destroyer) both broke up high in the atmosphere, raining debris down over very wide areas.

Of course, the die-hard fan might claim that the Star Destroyer is much tougher than a 20th century spacecraft, and would reach the ground intact.  In this case, the kinetic energy would be adsorbed by the ground, not the atmosphere.  We can simulate that as well, by using a solid iron meteorite of the same mass (only 232 meters across, due to the higher density), with a vertical descent.  It still imparts 400 megatons of kinetic energy on the planetary surface. But instead of an airblast, we end up with a crater 4.5 km in diameter, and half a km deep.  Nothing of this scale is evident in the Star Wars teaser.

As shown in the Chelyabinsk post a few years ago, the speeds- and energy- associated with space travel are so huge that even the most creative minds of Hollywood are unable to grasp their enormity and power. This was forgivable 30 years ago, before the internet, but in this day and age, fantastical videos that are tamer than reality are disappointing.

Related post: Viewing Imaginary Spacecraft from the Ground"

Wednesday, April 15, 2015

The expat Chestnut

The story of the American Chestnut is a real-life ecological morality play, that I have been familiar with ever since I was young enough to recognize the red moldering logs for what they were.  Whole books have been written about the destruction of Chestnut forests, and internet summaries abound. Since then, I have moved to Australia, settled down, and, in due course, bought a house and started playing with the yard. Australia is renown for its biosecurity, and there is no endemic chestnut blight here.  A few years ago, I started a search to see if I could find some American Chestnut trees, to see if they would grow here. 

Canberra is not the ideal climate for chestnut trees.  The annual rainfall here is about half what it is in the eastern US, and there are soil fungi in some areas which will kill their roots.  Never-the-less, after a few years of false leads, last autumn, I managed to get my hands on a few seedlings.  I planted three in my yard.  The first, planted in the chook pen, leafed out in spring, but never really grew much, and during the February-March dry spell, it turned brown and shriveled up.

The second tree is in the western corner of the yard, where it is exposed to both the hot westerly winds and the cold southerlies.  While it didn't grow much, It did hang onto its leaves until the first cold night, and it is now changing color.  I don't know how it will cope with the native acacias around it, and whether their shade will help reduce evaporation or their competition for moisture will hinder, but it seems to have made it through the first year.

The third tree is in a more sheltered position, where it gets morning sun but is sheded for the rest of the day by the neighbour's hedge.  It has only just begun to change leaf colors, and put on a decent growth this year.  By North American standards, the Canberra winters are not particularly harsh, so hopefully these trees will enter dormancy, sleep well through the winter, and continue to grow.
The half-dozen or so North American trees commonly planted here have a mixed history.  The tulip trees tend to suffer and die off at their tops during drought years, and the sweet gums and pin oaks also suffer during long dry hot spells.  But there are quite a few upland oaks which are doing OK. Only time will tell how Castanea dentata fares in this strange new world.

Wednesday, April 01, 2015

Book review: The Wife Drought

The Wife Drought, by Anabelle Crabb, describes the structural challenges women face in demanding careers due to the fact that male human workers with families are much more likely to get their partner to cover more of the familial duties than females are.  Ms. Crabb is envious of this, and covets a wife herself.  The book examines ways in which demanding careers are juggled with family responsibility, particularly by women, and the ways in which society can make it harder than necessary for men to bear more of the parental role.
  Crabb’s conception of a wife is best described in her own words:

“A `wife’ can be male or female.  Whether they’re a man or a woman, though, the main thing wives are is a cracking professional asset.  They enable the busy full-time worker to experience the joy and fulfillment of children, without the considerable inconvenience of having to pick them up from school at 3pm, which - in one of the human experience’s wittier little jokes – is the time that school ends, a time that is convenient for pretty much no one.  Having a wife means that if you get caught up at work, or want to stay later, either to get some urgent job finished or to frown at your desktop computer in a plausible simulacrum of working in order to impress a new boss while actually reading buzzfeed, it can be done.  Many wives work, but they do jobs that are either part-time or offer sufficient flexibility for the accommodation of late-breaking debacles.
            “In the olden days, wives were usually women.  Which is funny, because nowadays wives are usually women too.

After defining what a wife does, the book then probes how domestic duties are split among working family households (unevenly), how much of a professional asset a wife actually is, what the various means of coping without one are, and what societal pressures are preventing men from taking up wivery in any significant numbers.

The book is easy to read and extremely witty. Longtime readers of this blog will know that in the 9 years or so that I’ve been blathering here, I have had two children and four jobs, with weekly working hours varying from 1.5 to 7 days/week, in both office, lab and FIFO working environments. As my wife also works, figuring out how to juggle it all has been one of our greater challenges over the past few years.  So I found the content insightful and interesting, if not a bit sobering.  The sad fact of the matter is that there is no magic “have-it-all” solution.  Each week only has 168 hours, and they all need to be covered.  At the same time, this book makes it abundantly clear that, in many cases, it is women who are covering many of those hours, often by default.

There were a few things that I found somewhat odd, though.  In the middle of te book, Crabb intersperses data on average Australians with anecdotes of how people cope. However, very few of the people are average- they are mostly the once percent of the one percent- government ministers, high power lawyers, etc..  While this is not particularly surprising for someone of her profile, it is not necessarily that useful for the rest of us mere mortals.

The book winds up with a call to make it more socially acceptable for men to have more family time.  While I certainly agree with this sentiment, I have never encountered many of the cultural barriers that she describes. The closest thing I’ve had to a step-away-from-the-baby moment I’ve had was when I went to a Parents’ Group meeting when our daughter was small- They specifically called it Parents’ Group, not Mother’s group, so why not?  Afterwards the coordinator pulled me aside and said, “Look, I know it’s called Parents’ Group for political reasons, but some of the Mothers aren’t comfortable with dad’s around.”

I’ve been seeing those mothers at baby events, toddler events, and school for the last 7 years now, and not had any trouble from them, though.  Or their husbands.  Every employer I’ve had has been happy to offer family flexibility, although there has been a case where I’ve asked for family time and been given a raise to increase care instead.

On the other hand, most of the “manhood “ comments relating to hands-on parenting described in Crabb’s book seem to come from inner city paper pushers.  Most of the time when I was out and about with a baby was during my off weeks when I was working FIFO in the Northern Territory, so it maybe an outback industry job acts as a magic talisman against the pressed shirt preeners who measure their manhood by how hard they ride their cubicles. I never thought of this until I read this book, but it is the sort of book that makes one pause and shift one’s perspective of the framework under which we keep work and kids coexisting.  This is why I recommend that any of y’all with a job and a child read The Wife Drought.