Using the @PhETsims Blackbody Spectrum simulator, you can employ the color of the very hot stage 2 booster engine on the Falcon 9 to estimate its temperature. It glows deep red, so its temperature is at least ~5000K. https://phet.colorado.edu/sims/html/blackbody-spectrum/latest/blackbody-spectrum_en.html https://twitter.com/drsekula/status/1328135745148751872/photo/1 https://chirp.cooleysekula.net/attachment/68925