Wren Trelawny

Limiting magnitude from first principles

Where the fifth root of 100 comes from, why 5 log D is just Pogson again, and why every aperture table you have seen is a point source table.

I lost a won endgame and I want you to see it

A Lucena position I knew cold, and the one move on move 61 where I stopped asking which piece was supposed to move. Full annotation, clock times included.

Cape Wrath Trail, eleven days, and everything that got wet

Eleven days from Fort William to the lighthouse: the day by day numbers, the order in which everything got soaked, and the two days I would like back.

Your pack is four kilos heavier than you think

How to weigh a pack honestly, bin bag and wet tent included, and the point where cutting grams stops buying you speed and starts costing you sleep.

Marcus Aurelius at four in the morning

How the Meditations read on a night shift. Book 5.1 is written for people who choose when their day starts. 8.36 is the one that gets me to five in the morning.

Rust removal, five methods, one winner

I sheared a rusty belt guard into five coupons and gave each one a different treatment. Times, costs, mass loss, and what each did to the metal underneath.

My sky is not dark and I have the numbers

Two years of SQM-L readings from one hole in my lawn, the night a floodlight went up next door, and what 0.33 mag/arcsec^2 costs in hours.

How to read a supplement study in nine minutes

The order I read them in, the specific red flag at each step, and one clean trial walked through end to end. Most papers fail before minute three.

The Bristol Channel and a very confused datum

Chart Datum at Avonmouth sits 6.50 m below Ordnance Datum Newlyn. Here is the arithmetic that goes wrong when a height file does not name its zero.