🌌 astroterm

astroterm is a terminal-based star map written in C. It displays the real-time positions of stars, planets, constellations, and more, all within your terminal—no telescope required! Configure sky views by date, time, and location with precise ASCII-rendered visuals. See usage for all supported options!

astroterm is constantly improving, and we'd love to hear your ideas! If you have a suggestion or find a bug, please open an issue and share your feedback.

The night sky above above Singapore on January 2, 2025

Table of Contents

• 🌌 astroterm
  • Features
  • Installation
    • Homebrew
    • Nix (unstable)
    • Prebuilt Executable
  • Building from Source
    • Linux, macOS & WSL
    • Windows
  • Usage
  • Troubleshooting
  • Citations
  • Data Sources

Features

• 🔭 Highly Customizable: Choose any date, time, and location to explore past, present, or future celestial events
• 📐 Accurate Rendering: View the moon, stars, and planets with as much precision as terminal graphics allow
• 🌘 Moon Phases: Precise lunar phases in real-time
• 🌌 Constellation Figures: Detailed constellation shapes
• ⚡ Performance Optimized: Lightweight and fast ASCII rendering

Stars over Sydney, Australia on January 6, 2025

Installation

Several installation methods are provided based on your platform. If none of these fit your needs, you can always build from source. Refer to troubleshooting for help resolving any issues.

Homebrew

You can install Astroterm directly from the custom Homebrew tap:

brew tap da-luce/astroterm
brew install astroterm

Nix (unstable)

As of January 15, 2025, astroterm has been merged into the main branch of nixpkgs. It may take a few days to propagate to the unstable branch. Once it is available, you can install it using:

nix-channel --add https://nixos.org/channels/nixpkgs-unstable unstable
nix-channel --update
nix-env -iA unstable.astroterm

Prebuilt Executable

Unix

1. Download the latest executable using wget

   wget -O astroterm "https://github.com/da-luce/astroterm/releases/latest/download/astroterm-<os>-<arch>"

   • Replace <os> with the appropriate platform:
     • Linux: linux
     • macOS: darwin
   • Replace <arch> with the appropriate architecture:
     • Linux: x86_64 (arm64 support to come after Ubuntu arm64 runners are avilable)
     • Apple Silicon (M-series): aarch64
     • Intel-based Macs: x86_64
   • To view all supported combinations, see the Releases page.

2. Run the executable

   chmod +x ./astroterm
   ./astroterm

Windows

1. Download the latest .exe file using PowerShell's Invoke-WebRequest:

   Invoke-WebRequest -Uri "https://github.com/da-luce/astroterm/releases/latest/download/astroterm-win-x86_64.exe" -OutFile "astroterm.exe"

2. Run the .exe

   .\astroterm.exe

Building from Source

Linux, macOS & WSL

Requirements

Important

When building, you must install the development version of the runtime requirements, which provide the headers and libraries necessary for compiling and linking. These packages are typically marked with a -dev or -devel suffix.

• Unix-like environment (Linux, macOS, WSL, w64devkit, etc.)
• C compiler
• ncurses library
• Some common CLI tools
  • wget or curl
  • xxd (is also commonly packaged with vim)
  • pkg-config

Install

1. Clone the repository and enter the project directory:

git clone https://github.com/da-luce/astroterm && cd astroterm

2. Download star data:

curl -L -o data/bsc5 http://tdc-www.harvard.edu/catalogs/BSC5

3. Build:

make

Windows

Warning

Building on Windows is more involved than other platforms.

Requirements

• w64devkit
• pdcurses*

Install

1. Clone the repository and enter the project directory:

git clone https://github.com/da-luce/astroterm && cd astroterm

2. Download star data:

curl -L -o data/bsc5 http://tdc-www.harvard.edu/catalogs/BSC5

3. Build:

make

Usage

Options

The --help flag displays all supported options:

Usage: astroterm [OPTION]...

  -a, --latitude=<degrees>  Observer latitude [-90°, 90°] (default: 0.0)
  -o, --longitude=<degrees> Observer longitude [-180°, 180°] (default: 0.0)
  -d, --datetime=<yyyy-mm-ddThh:mm:ss>
                            Observation datetime in UTC
  -t, --threshold=<float>   Only render stars brighter than this magnitude
                            (default: 5.0)
  -l, --label-thresh=<float>
                            Label stars brighter than this magnitude (default:
                            0.25)
  -f, --fps=<int>           Frames per second (default: 24)
  -s, --speed=<float>       Animation speed multiplier (default: 1.0)
  -c, --color               Enable terminal colors
  -C, --constellations      Draw constellation stick figures. Note: a
                            constellation is only drawn if all stars in the
                            figure are over the threshold
  -g, --grid                Draw an azimuthal grid
  -u, --unicode             Use unicode characters
  -q, --quit-on-any         Quit on any keypress (default is to quit on 'q' or
                            'ESC' only)
  -m, --metadata            Display metadata
  -r, --aspect-ratio=<float>
                            Override the calculated terminal cell aspect ratio.
                            Use this if your projection is not 'square.' A value
                            around 2.0 works well for most cases
  -h, --help                Print this help message
  -i, --city=<city_name>    Use the latitude and longitude of the provided city.
                            If the name contains multiple words, enclose the
                            name in single or double quotes. For a list of
                            available cities, see:
                            https://github.com/da-luce/astroterm/blob/main/data/
                            cities.csv
  -v, --version             Display version info and exit

Example

Say we wanted to view the sky at 5:00 AM (Eastern) on July 16, 1969—the morning of the Apollo 11 launch at the Kennedy Space Center in Florida. We would run:

astroterm --latitude 28.573469 --longitude -80.651070 --datetime 1969-7-16T8:00:00

Finding the precise coordinates can be cumbersome, so we could also use the nearest major city to achieve a similar result:

astroterm --city Orlando --datetime 1969-7-16T8:00:00 -m

While we're still waiting for someone to invent time travel, we can cheat a little by using Stellarium to confirm that this aligns with reality.

If we then wanted to display constellations and add color, we would add --constellations --color as options.

If you simply want the current time, don't specify the --datetime option and astroterm will use the system time. For your current location, you will still have to specify the --lat and --long options, or provide the nearest city with the --city option.

For more options and help, run astroterm -h or astroterm --help.

Tip

Use a tool like LatLong to get your latitude and longitude.

Tip

Star magnitudes decrease as apparent brightness increases, i.e., to show more stars, increase the threshold.

Troubleshooting

Release Won't Download via Curl

For some reason, curl does not follow the latest release redirect. Use wget to download the latest release or hardcode the tag in the link using curl. Or, just download via the releases page.

Broken Unicode on Linux

If Unicode characters do not display correctly in the terminal, you may need to configure your system's locale to support Unicode.

1. Temporarily set the locale (add this to .bashrc or equivalent to permanently enforce)

export LC_ALL="en_US.UTF-8"
export LC_CTYPE="en_US.UTF-8"

2. Install and configure locales (example for Ubuntu/Debian)

sudo apt update
sudo apt install -y locales
sudo dpkg-reconfigure locales

During configuration, select en_US.UTF-8 as the default locale.

Development

Testing

Run make check.

Citations

Many thanks to the following resources, which were invaluable to the development of this project.

• Map Projections-A Working Manual by John P. Snyder
• Wikipedia
• Atractor
• Jon Voisey's Blog: Following Kepler
• Celestial Programming: Greg Miller's Astronomy Programming Page
• Practical Astronomy with your Calculator by Peter Duffett-Smith
• NASA Jet Propulsion Laboratory
• Paul Schlyter's "How to compute planetary positions"
• Dan Smith's "Meeus Solar Position Calculations"
• Bryan Weber's "Orbital Mechanics Notes"
• ASCOM
• A Fast Bresenham Type Algorithm For Drawing Ellipses

Data Sources

• Stars: Yale Bright Star Catalog
• Star names: IAU Star Names
• Constellation figures: Stellarium (Converted from Hipparchus to BSC5 indices using the HYG Database—see convert_constellations.py)
• Cities: GeoNames (Filtered and condensed using filter_cities.py)
• Planet orbital elements: NASA Jet Propulsion Laboratory
• Planet magnitudes: Computing Apparent Planetary Magnitudes for The Astronomical Almanac