cosmo. Be an adult, use the terminal.

Motivation

There are several cosmology calculations that are frequently used in astronomy and cosmology calculators have become a staple. The most popular one being Ned Wrights cosmology calculator, which many people have improved upon, notably ICRAR's version by Aaron Robotham (which this tool is largely inspired by).

In addition, there are several software packages available in many languages for performing these same cosmological calculations, most popular by far the astropy cosmology module.

However, personally, if I want to quickly calculate a co-moving distance, or angular scale or the age at a particular redshift then I don't want to open a web browser or write python code! Instead, I just want to run a command in the terminal and have the answer instantly.

cosmo is a CLI tool that aims to address this niche and provides basic cosmological functions directly from the terminal.

Usage

cosmo has a very usable help function that can be used for the main command via cosmo --help which will list all the possible sub-commands. All of these also have --help which will describe the available arguments.

Adopting a cosmology

For all commands the cosmological parameters can be set with --omega-m, --omega-lambda, --omega-k, and the --hubble-const or their short equivalents -m, -l, -k, -H respectively. For example, calculating the co-moving distance at redshift 0.3, using the Plank 13 cosmology (H0 = 67.3, Omega matter = 0.315, Omega Lambda = 0.685, Omega k = 0.) can be done like this

cosmo codist 0.3 -m 0.315 -l 0.685 -H 67.3

The default values for cosmo is a vanilla 737 cosmology (H0 = 70, Omega matter = 0.3, Omega Lambda = 0.7, Omega k = 0.) Each one of these values will be adopted if they are not given explicitly.

At the moment cosmo is built for flat cosmologies and will raise an error for open or closed universes

Sub-commands

all

For most use-cases, cosmo all <z> will be sufficient. This returns a summary representation of the most common cosmological properties at a given redshift

cosmo all 1

This will also show additional values which haven't been included as an official sub-command.

Co-moving distance

Co-moving distance at a given redshift in Mpc.

cosmo codist 0.3

The -i --inverse flag can be used to calculate the redshift at a given distance which is given in Mpc.

cosmo codist -i 100

Luminosity distance

Luminosity distance at a given redshift in Mpc.

cosmo lumdist 0.3

The -i --inverse flag can be used to calculate the redshift at a given distance which is given in Mpc.

cosmo lumdist -i 100

Co-moving volume

Co-moving volume at a given redshift in Gpc³.

cosmo covol 0.3

The -i --inverse flag can be used to calculate the redshift at a given volume which is given in Gpc³.

cosmo covol -i 3.14

Look-back time

Look-back time at a given redshift in Gyr.

cosmo lookback 0.3

The -i --inverse flag can be used to calculate the redshift at a given look-back time which is given in Gyr.

cosmo lookback -i 3.14

Distance modulus

Distance modulus at a given redshift in magnitudes.

cosmo distmod 0.3

Physical angular scale

The physical on-sky angular scale at a given redshift. The default value is returned in kpc/arcsec.

cosmo angscale_phys 0.3

*The physical scale is also the default value for angular scale and can also be calculated just using angscale

cosmo angscale 0.3

The -M --mpc-per-arcmin flag can be used to return the value in units of mpc/arcmin instead of kpc/arcsecond.

cosmo angscale -M 0.3

Co-moving angular scale

The co-moving on-sky angular scale at a given redshift. The default value is returned in kpc/arcsec.

cosmo angscale_phys 0.3

The -M --mpc-per-arcmin flag can be used to return the value in units of mpc/arcmin instead of kpc/arcsecond.

Installation

Downloading the binary

The binary for cosmo is only available on mac-os but will be made available on Linux soon.

Installing dog is very easy

curl -L -o dog https://github.com/trystanscottlambert/cosmo/releases/download/v1.0.0/cosmo
chmod +x cosmo
sudo mv cosmo /usr/local/bin/

You may need to start a new terminal to get it working.

If you don't want to install the binary then you can compile the program from source using 'cargo'.

Compile from source

If you are using Linux or don't want to download a binary file then cosmo can be built from source using cargo.

First make sure you have rust installed:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Download the cosmo repo with git

git clone git@github.com:TrystanScottLambert/cosmo.git

cd into the cosmo folder cd cosmo/

You should be able to see the Cargo.toml file. From here compile using cargo (which would already be installed with rust.)

cargo build --release

Then simply move the binary file into your /bin directory

sudo mv target/release/cosmo /usr/local/bin

You may need to restart the terminal. You can remove the cloned repo if you wish.