Friday, October 21, 2016

Tuesday, October 18, 2016

Sunlight Through Colored Glass

The handled jug, gold bottle, and small sea green vase belonged to my Grandmama.  The cobalt blue is a replacement for a close match I gave it away as a sorry/replacement for a china vase that Scaramouche knocked down and broke.  The red was just because I love crimson:

Kamiyo mo kikazu
Kara kurenai ni
Mizu kukuru to wa
                                                                         -Ariwara no Narihira, Hyakunin Isshu, poem 17

 Impassionate gods
Even in their time was it heard
Tatsuta river
 such crimson
water dyed

Friday, October 14, 2016

Horrifying Thoughts: What If the Moon Were At the Same Distance From Earth as the International Space Station?

The animation:
 Phil Plait explains just why this is horrifying (spoiler: tidal forces would leave the Earth scoured, cracked, and sloshing, and would rip the Moon to pieces.)

But the chances of this ever happening are extremely low (as in, lots of zeros after the decimal point low).  An old end-of-earth fantasy book I read as a child got it wrong: the Moon is not falling, and is in fact currently receding from us at roughly 4 cm/year.  (That rate is not constant.)

The physics are complicated.  (Very complicated.)  But we can outline the basics by talking about tidal forces.  The Moon exerts a gravitational pull on the Earth, squishing the Earth to slightly more like a football than a sphere, an oblate spheroid.  Earth's oceans can deform more to this pull than land, but because the Earth spins more rapidly than the Moon revolves, the bulge of the oceans is whirled slightly ahead of Earth-Moon shortest distance line.  Crash Course Astronomy has a good animation at about 5:00.

But this bulge has mass, and so it exerts a gravitational pull on the Moon, hurrying the Moon along.  The Moon also pulls back on the bulge, which drags on the Earth and slows down its rotation.

The net effect is to transfer energy to the Moon, causing it to speed up, and because of Kepler's Second Law (orbiting bodies sweep out equal areas in equal time, seen better with an animation), this moves the Moon farther away from the Earth.

There are lots of complicating factors: the shape of the continents (not constant), friction between the Earth and its oceans (imagine trying to model tidal forces during a global ice age!), the forces exerted on and by Earth's atmosphere, every other non-negligible body in the solar system exerting its own gravitational force into the mix, orbital mechanics, etc.

Ask an Astronomer has a nice write-up without math.  I don't have a good source for those wanting math, but I'm starting with Lunar Orbital Evolution: A Synthesis of Recent Results from 1999 (I know, not that recent, but free.)  If you, gentle reader, have a relevant article that you found helpful, please leave the title and a link in the comments.

Tuesday, October 11, 2016

Things In My Garden

A tenacious rose.  After we hacked down and dug up the prickly holly bush that was in this spot, this rose appeared and is enthusiastically putting out new leaves.  I can't wait to see what color it is! 

Sunday, October 9, 2016

From the Minutes of the Cthulhu Prayer Breakfast with Muffins and Mimosas

It has been so concluded that it were a matter of horror should cockroaches contract the zombie plague. Upon considering the impossibility of sealing a spaceship, or anything else, against cockroaches, thus implying that fleeing a doomed and zombie cockroach-plagued earth would be impossible, as humans would inadvertently be transporting some cockroaches with them wherever they went, some of the members present considered fainting. This course of action was, however, abandoned with the very practical consideration that smelling salts have yet to be synthesized.