# astro bits

### Conversions

Convert Gaussian $\sigma$ to FWHM with $FWHM = 2.35482 \, \sigma$

The sky is 41252.961 square degrees, that’s $5.34638 \times 10^{11}$ square arcseconds or $2.35 \times 10^{-11}$ steradian per sq arcsecond.

### astro-ph

When submitting a MNRAS paper to astro-ph, to make it look nice on US letter paper (rather than A4) you should use these at the top of your TeX file.

\documentclass[usenatbib,letterpaper]{mn2e}
\usepackage[totalwidth=480pt,totalheight=680pt,layoutvoffset=0.5cm]{geometry}

### Codes

#### Mercury

John Chambers’ web page with Mercury doesn’t work any more, but the code seems easy enough to find. There is a binary star version around too. If you get it make sure you implement the bug fix, I found that the binary star version wouldn’t work sensibly until I added it (would die when anything was ejected).

#### Swift

Watch out if you change the swift.inc file in the standard download of swift, say for the number of test particles. The programs point to two different swift.inc files, one in the root dir and one in the main dir (and another in the tools dir). You could change them both, I removed the one in the main dir and made a symbolic link.

If you try swift you’d be silly not to check out SwiftVis, very clever but make sure you allocate lots of memory with -Xmx2000M or something.