Alpha Centauri A is the same spectral type as, and similar in size to the Sun.

This December, NASA is launching an instrument to the International Space Station to continue monitoring the Sun’s energy input to the Earth system. The Total and Spectral solar Irradiance Sensor (TSIS-1) will precisely measure what scientists call “total solar irradiance.”

They all agreed that it was a huge creature, luminous, ghastly, and spectral.

Satellite instruments measure light emitted or reflected back to space at different wavelengths and create spectral reflectance curves.