- Znotes - https://znotes.org/ib/middle-years-program/physics/theory/astrophysics/
- https://lambda.gsfc.nasa.gov/product/suborbit/POLAR/cmb.physics.wisc.edu/tutorial/briefhist.html#:~:text=An astronomer named Eudoxus created,the Earth at its center.
- https://www.khanacademy.org/science/in-in-class11th-physics/in-in-phy-gravitation/in-in-gravity-newtonian/a/newtons-law-of-gravitation-ap1#:~:text=Newton's universal law of gravitation&text=Every object in the universe,along a line joining them.&text=The force is directly proportional,between their centers of mass.
- https://www.esa.int/Education/1._Introduction#:~:text=In astronomy%2C a satellite will,it is not man-made.
- https://pages.uoregon.edu/soper/Stars/brightness.html#:~:text=The apparent brightness is how,book calls it apparent magnitude .)
- https://www.e-education.psu.edu/astro801/content/l4_p5.html - Apparent magnitude
- https://www.e-education.psu.edu/astro801/content/l4_p4.html - Apparent Brightness
- https://wwelsh.sdsu.edu/~wwelsh/CLASSES/ASTROBIO/LECTURES/wien_law.pdf
- https://www.e-education.psu.edu/astro801/content/l4_p3.html
- https://dbpedia.org/page/Areosynchronous_orbit
- https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introductory_Chemistry_(CK-12)/05%3A_Electrons_in_Atoms/5.05%3A_Atomic_Emission_Spectra