## Tuesday, March 27, 2018

### Will the Falling Chinese Satellite Hit Someone?

As you probably know, the de-orbiting Chinese space station Tiangong-1 will soon fall to Earth.

This thing is 10.4 meters long and, on launch, weighted 8.5 tonnes.

What are the chances it will hit someone, or something important?

I don't know, and now that I'm reviewing this calculation I feel pretty sure I don't know, but here goes with my original idea.

The satellite will fall between the ± 43° latitude lines. But that's about all that seems known for sure right now.

That area constitutes 348 Mkm2, or 68% of Earth's surface area.

Much of this is ocean, but I don't know exactly how much. I'll assume, for better or worse, that it's the same percentage that the ocean makes up of Earth's total surface area, 70.8%, giving a potential land fall area of 102 Mkm2.

How many people are in this area? I don't know. All I know to do (without a lot of work) is assume it's the same percentage of the world population as is land, which, extrapolating this trend, was 7.46 B in 2017.

(Amazingly, 90% of the world's people live in the Northern hemisphere.)

When might a person be "hit" by a falling satellite? Let's say if it occurs within a 10 m radius of that person. Thus the danger zone around each person is 628 m2, and around all people living in the fall zone is (assuming independence) 3.20 Mkm2.

That's 3.1% of the satellite's potential landing zone. Small, but not tiny.

--

I suspect this number is an overestimate, because

(1) I've overestimated the number of people who live between -43 and +43 degrees latitude, since there's more ocean there than I've assumed, and
(2) I've assumed each person's "target zone" is independent of everyone else's (which is obviously not true in cities.)

Much of Europe and Russia lives above 43° N latitude, and all of Canada does -- and I do too, at 45-epsilon degrees. (I often drive past the a sign in North Salem announcing the 45° line, and based on my home's GPS coordinates I've calculated that I'm about 4.4 km south of this line, or at 44.960858° north latitude.)

So, there's a tiny chance of someone being hit by this satellite. 3% seems high -- but I doubt the chances are infinitesimal, even if I'm off by a factor of 10.

Still, good luck out there. Heads up.

### Free, Online Climate Textbooks

I've recently come across a few free, online climate textbooks, and thought it worth mentioning here.

A great introduction to the basics:

Introduction to Climate Science, Andreas Schmittner, Oregon State University.

Introduction to climate dynamics and climate modeling, by Goosse H., P.Y. Barriat, W. Lefebvre, M.F. Loutre and V. Zunz, (2008-2010).

I guess I can mention Pierrehumbert's textbook Principles of Planetary Climate, though I'm not sure it's on the Web legally. I bought the hardback version and have learned a great deal from it. I heartily recommend it.

## Sunday, March 18, 2018

### My Plastic Brain by Caroline Williams

From my mailbox:

My Plastic Brain: One Woman's Yearlong Journey to Discover If Science Can Improve Her Mind by Caroline Williams.

Amazon
Barnes and Noble

Author's Web site

From Kirkus Reviews:

"Readers hoping to improve their own cognitive abilities may feel a bit of a letdown by the author’s old-fashioned, down-to-earth advice: exercise your body, preferably outdoors, learn mindful meditation but also allow your mind to wander, engage in a mentally challenging hobby, and pick the skill you want to improve and practice it in real life."

Valar morghulis.

## Thursday, March 15, 2018

### 'Mind over matter': Stephen Hawking – obituary by Roger Penrose | Science | The Guardian

The best Hawking obit I've read:

https://www.theguardian.com/science/2018/mar/14/stephen-hawking-obituary

## Monday, March 12, 2018

### When the Statue of Liberty Gets Sea Walls

Last night I started watching The Expanse on Amazon Prime. It's been really good scifi so far, and has that nitty-gritty view of future space travel, more Firefly than Star Trek, but even grittier. It's set 200 years in the future, and in an early episode there was this short cut of the Statue of Liberty, with sea walls due to (presumably) global warming:

Another good idea (for the story, at least) was "gravity torture," where those who grew up off-Earth in a lower gravitational environment are tortured by being hung in Earth's gravity for hours:

In Kim Stanley Robinson's Mars Trilogy, kids born on Mars (where g = 38% of that of Earth) eventually become significantly taller than Earthlings.

I appreciate when writers think about the little things and subtly put them in their stories. It's fun to notice them. The Expanse does this very well, so far.

## Sunday, March 11, 2018

### Question About My Blog's Appearance

When you read this blog, is the page too wide for your screen?

Do you have to scroll right in order to see what's beyond the post itself -- the "About Me" module, "Blog Archive," "Good Links," etc.?

I do. So I'm wondering if everyone has the same problem. Other blogspot blogs read fine in my browser.

Thanks.

## Thursday, March 01, 2018

### Equations That Changed the World

A few years ago, mathematician Ian Stewart published a book titled 17 Equations That Changed The World. It's an interesting list:

I would go beyond these 17 and add:
• 1+1=2, which some unknown someone realized long ago was profound and incredibly useful. The logical proof of this assertion, though, didn't come until Bertrand Russell and Alfred North Whitehead three-volume Principia Mathematica. It's a crazy book -- the text looks almost alien or elvish, and it took them several hundred pages of work before they could prove that 1+1=2. Russel said his work on this book "had actually damaged his brain." Here's an interesting discussion of the Principia Mathematica from NPR in 2010.
• Newton's second law of motion, F=ma (really, F=dp/dt, the time rate of change of momentum).
• Planck's Law of radiation (probably).
• The Lagrangian of quantum electrodynamics, because it changed how quantum physics was done ever afterward.
• Einstein's equations of general relativity, because they changed our view and understanding of the universe, and for their sheer elegance and sophistication.
You?