What Major Contribution Did the German Mathematician Karl Friedrich Gauss $\sigma$

What major contribution did the German mathematician Karl Friedrich Gauss make to astronomy?

A) He discovered a regular progression of planetary distances from the Sun, so that each planet's orbit could be calculated knowing the distance of any one planet from the Sun.
B) He developed a method for computing an object's temperature from measurements of the intensity of emitted light at only two wavelengths.
C) He derived the Stefan-Boltzmann law, emitted flux = $\sigma$ T⁴, mathematically, from basic physical principles.
D) He developed a method for computing an object's orbit from only three observations.