Archive for November 2, 2011

Transfer Orbit

Posted in Cute Problems, The Universe and Stuff with tags , on November 2, 2011 by telescoper

From time to time I like to post nice physics problems on here. Here is a quickie that I used to use in my first-year Astrophysical Concepts course which has now been discontinued, so I don’t need to keep it to myself it any longer.

A simple way to travel from one planet in the solar system to another is to inject a spacecraft into an elliptical transfer orbit, like the one shown by the dashed curve, which is described by Kepler’s Laws in the same way that the planetary orbits (solid curves) are.

Kepler’s Third Law states that the  period of an elliptical orbit is given by P^2 \propto a^3 where a is the semi-major axis of the ellipse. Assuming that the orbits of Earth and Mars are both approximately circular and the radius of Mars’ orbit is 50% larger than Earth’s, and without looking up any further data, calculate the time taken to travel in this way from Earth to Mars.

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November Graveyard

Posted in Poetry with tags , , on November 2, 2011 by telescoper

All of a sudden it’s November and the arrival of the new month has found me in the mood for a bit of Sylvia Plath. This is November Graveyard, read by the poet herself in that uniquely unsettling voice of hers. Sylvia Plath was born in America but eventually moved to England after she married the poet Ted Hughes. Her accent sounds to me neither American nor British. Her diction, as polished as cut glass but also as brittle, is that of a person striving  to re-invent herself. And failing. Her voice sounds to me redolent with alienation, and its coldness gives this reading of this bleak poem an even harder edge than the text alone.  Plath took her own life in 1963 and was subsequently buried in the same graveyard referred to in the poem,  in Heptonstall, Yorkshire.

The text, as read, differs from some published versions:

The scene stands stubborn: skinflint trees
Hoard last  leaves, won’t mourn, wear sackcloth, or turn
To elegiac dryads, and dour grass
Guards the hard-hearted emerald of its grassiness
However the grandiloquent mind may scorn
Such poverty. So no dead men’s cries

Flower forget-me-nots between the stone
Paving this grave ground. Here’s honest rot
To unpick the elaborate heart, pare bone
Free of the fictive vein. When one stark skeleton
Bulks real, all saints’ tongues fall quiet:
Flies watch no resurrections in the sun.

At the essential landscape stare, stare
Till your eyes foist a vision dazzling on the wind:
Whatever lost ghosts flare,
Damned, howling in their shrouds across the moor
Rave on the leash of the starving mind
Which peoples the bare room, the blank, untenanted air.