References:
https://lco.global/spacebook/galaxies/history-discovery/
https://science.nasa.gov/people/edwin-hubble/
https://www.eso.org/public/blog/first-rung-on-cosmic-distance-ladder/
https://www.aanda.org/articles/aa/full_html/2019/08/aa35980-19/aa35980-19.html
https://arxiv.org/pdf/1710.06489.pdf
https://link.springer.com/article/10.1007/s00407-006-0118-4
https://pwg.gsfc.nasa.gov/stargaze/Shipparc.htm
https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1600-0498.1969.tb00145.x
https://www.jstor.org/stable/41133426
https://journals.sagepub.com/doi/10.1177/0021828618817175
https://pwg.gsfc.nasa.gov/stargaze/Shipparc.htm
https://www.cosmos.esa.int/web/hipparcos
https://hdl.huntington.org/digital/collection/p15150coll7/id/6331/rec/3
https://apod.nasa.gov/diamond_jubilee/papers/trimble.html
https://science.nasa.gov/missions/hubble/hubble-views-the-star-that-changed-the-universe/
https://apod.nasa.gov/debate/debate20.html
https://www.pnas.org/doi/10.1073/pnas.15.3.168
https://www.pnas.org/doi/10.1073/pnas.1424299112
https://arxiv.org/pdf/1301.7286.pdf
http://www2.lowell.edu/workshops/slipher/Slipher1913LowOB2_56S.pdf
https://www.youtube.com/watch?v=wYmuSAZiILM
https://iopscience.iop.org/article/10.1086/300499
https://iopscience.iop.org/article/10.3847/1538-4357/aaa5a9
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC33557/
https://iopscience.iop.org/article/10.1086/300499/pdf