skymap MiniHOWTO draft

README-skymap.md

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+# skymap Mini HOWTO
+HOWTO find a particular satellite for viewing with skymap
+for use with stvid imaging.
+
+From notes by Cees Bassa mixed with my misunderstandings.
+This example will use the Bluewalker 3 satellite, with NORAD ID 53807.
+
+
+First a TLE is needed. I get this from Celestrak, ala:
+
+```
+wget -O ~/devel/spacecruft/TLE/bluewalker3/bluewalker3.tle \
+  "https://celestrak.org/NORAD/elements/gp.php?CATNR=53807"
+```
+
+Should look something like this:
+
+```
+BLUEWALKER 3            
+1 53807U 22111AL  22323.16311390  .00001894  00000+0  10565-3 0  9997
+2 53807  53.2016 312.3504 0014195 129.0685 231.1577 15.18596984 10510
+```
+
+Run skymap (with my branch):
+
+```
+#!/bin/bash
+
+LENGTH=86400 # Seconds, 86400 = 1 day
+TIME="2022-11-12T12:50:00.000"
+TLE=~/devel/spacecruft/TLE/bluewalker3/bluewalker3.tle
+
+skymap									\
+	-s 9920								\
+	--no-stars							\
+	--width=1600							\
+	--height=1000							\
+	--all-objects							\
+	--nmax=128							\
+	-l ${LENGTH}							\
+	-c ${TLE}							\
+	-t ${TIME}
+```
+
+![skymap tutorial 1](img/skymap-tutorial-01.png)
+
+
+That's a 24h prediction for BW3 for your location. Grey tracks are in the shadow, orange tracks are in sunlight but during daytime, yellow tracks are in sunlight but during night time
+
+
+So you have two passes during night time. Low South East, and low South West
+Now in interactive mode, use `l` to change the track length to 3600 secs (1 hour)
+Then use `.` to move time forward with these 1 hour steps.
+
+At some point you'll get the first pass.
+then use `<` a few times to reduce the timestep size to something like 450 seconds and then step forward with `.` until it is above the horizon
+
+
+This is what I get moving time forward to 00:37:37
+pressing `i` with the cursor near 53807 gives you the az/el and RA/Dec to read off
+10:27
+
+I dumped the TLE for 53807 into a text file with tleinfo -i 53807 >53807.txt
+