starmap

The naked-eye sky in a terminal, drawn in braille. Part of the Fe₂O₃ Rust terminal suite.

Two tables live in the library, so nothing is fetched and nothing is cached:

• 9,096 stars from the Yale Bright Star Catalogue, with Hipparcos distances for 7,369 of them, plus B−V colour, spectral type, HD / HIP numbers and IAU proper names.
• 150 constellation strokes from d3-celestial.

Two skies

use starmap::{panel, Opts, Projection, View};

// What is over your head right now.
let sky = View::new(Projection::Horizon { lst_deg: 212.4, lat_deg: 59.9 });
print!("{}", panel(&sky, &Opts::default(), &[], 1, 1, 100, 30));

// The northern half of the celestial sphere, as a map.
let map = View::new(Projection::Hemisphere { north: true });
print!("{}", panel(&map, &Opts::default(), &[], 1, 1, 100, 30));

Horizon puts the zenith at the centre and the horizon at the rim, north up and east to the left, which is what you get looking up rather than at a map. Hemisphere puts the pole at the centre and the equator at the rim, and reaches 30° past it so Orion stays whole on both halves.

Both are azimuthal equidistant, so zoom is a plain multiplication:

let mut v = View::new(Projection::Hemisphere { north: true });
v.zoom = 6.0;                       // six times in
v.pan = v.place(101.3, -16.7).unwrap();   // centred on Sirius

Picking a star

if let Some(p) = starmap::pick(map, Opts::default(), "Pick a star") {
    println!("{} at {:?} pc", p.star.label(), p.star.dist_pc);
}

Arrows walk a crosshair, + / - zoom about it, f flips north and south, c and n toggle the figures and the names, 0 resets, Enter takes the star under the cross. The star nearest the crosshair is named in the footer as you move, with its magnitude, spectral type and distance in light years.

What you get per star

pub struct Star {
    pub ra: f64, pub dec: f64,   // J2000 degrees
    pub mag: f64,                // apparent visual magnitude
    pub bv: Option<f64>,         // B−V colour index
    pub spectral: &'static str,  // "A1Vm"
    pub hd: u32, pub hip: u32,   // cross-ids, 0 if none
    pub dist_pc: Option<f64>,    // None where the parallax is not trustworthy
    pub name: &'static str,      // IAU proper name, or empty
}

absmag() gives absolute visual magnitude where the distance is known, which is what an HR diagram needs. label() always returns something to print: the proper name, else HD 48915, else HIP 32349.

Distance is None for 19% of the catalogue, either because the parallax came out negative or because it is worse than 20% uncertain. Betelgeuse is in that group: 7.63 ± 1.64 mas, which is exactly why its distance is still argued about. The library says it does not know rather than printing a number nobody should trust.

Drawing your own things on it

panel takes a slice of Body, for anything that is not a catalogue star:

let bodies = vec![starmap::Body {
    name: "jupiter".into(), ra: 128.4, dec: 19.2, rgb: (240, 205, 150), size: 1,
}];

That is how astro puts the sun, moon and planets on the sky it draws for the selected hour.

Cost

A frame is arithmetic over the two tables and one braille canvas: about 2 ms for a full screen, nothing at all between keypresses. The chart scales how faint it goes to the room it has and the zoom it is at, so a pane fifteen rows high shows the constellation stars and a full screen shows the sky.

Used by

• astro — the sky for the selected hour
• stars — pick a star off the sky and land on it in the Hertzsprung-Russell diagram

Data

Yale Bright Star Catalogue (public domain), Hipparcos parallaxes (ESA 1997, via VizieR), IAU Catalog of Star Names, and d3-celestial's constellation lines (BSD 3-clause, © Olaf Frohn). Full attribution in data/README.md.

License

Public domain (Unlicense), except the constellation-line table, which carries Olaf Frohn's BSD notice.

— Geir Isene