Petr Havel

About this profile

Who I am, what I teach, the things I refuse to post about, and a standing invitation to tell me my translations are wrong.

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.

Postmortem: 43 minutes of 502s and one very confident regex

Our gateway returned 502 for forty three minutes because of a regex I would have approved too. Full timeline, the pattern, and the dashboard that lied to me.

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.

Every projection is wrong, here is how much

Gauss closed this in 1827 and Tissot gave us a way to measure the damage. Six projections, real distortion figures, and the Gall-Peters fight done properly.

Same flour, same oven, four hydrations

Four doughs, one sack of flour, one bake. 65, 72, 80 and 88 percent hydration measured properly. 72 won, and the wettest dough lost badly.

218 hours on one galaxy

Three winters on NGC 891 from a Bortle 4 backyard. Full log, the square root maths on what each block of hours bought, and the 40 hours I deleted.

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.

Blitz ruined my calculation and I fixed it in 400 games

Four hundred tracked games, blunder rates by time control, and the two rules that halved mine. Includes every reason my own numbers should not convince you.

The five sentences in every fraudulent management letter

Five sentence archetypes I keep finding in letters management writes to auditors and boards, what each one is doing, and which one I circle in red.

Mapping my own light pollution

I put an SQM on a 1 km grid across Lisbon and made a lovely contour map of something that cannot honestly be contoured. Four months, one admission.