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://phys.libretexts.org/Bookshelves/Astronomy__Cosmology/Big_Ideas_in_Cosmology_(Coble_et_al.)/06%3A_Measuring_Cosmic_Distances/6.01%3A_Geometrical_Methods

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