Bob Moler's Ephemeris Blog

Monday, July 23rd. The Sun rises at 6:19. It’ll be up for 14 hours and 59 minutes, setting at 9:18. The Moon, half way from first quarter to full, will set at 3:41 tomorrow morning.

The accurate observational positions of Mars by Tycho Brahe allowed Johannes Kepler in the early 17th century to discover his three laws of planetary motion. Tycho was the last and greatest of the naked eye astronomers. Kepler befriended Tycho who jealously guarded his observations. It was only after his death in 1601 that Kepler took possession of Tycho’s data. Until then it was believed that planets moved with uniform circular motion, even though they didn’t look like it. Astronomers added circle after circle, called epicycles, to attempt to make their system work. Mars was the worst case. Kepler finally determined that Mars, and indeed all the planets, orbited the Sun in elliptical orbits. That was his first law of planetary motion.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

The source if the images below is the talk “Mars 2018” I gave at the Betsie Valley District Library, July, 20, 2018.

Tycho and Kepler. Artist for Tycho: Eduard Ender (1822-1883). Artist for Kepler, unknown. Source: Wikipedia.

Mars’ and Earth’s orbits to scale and positions of the Earth and Mars July 20, 2018, one week before opposition. Note that Mars’ orbit is decidedly not circular. Credit my LookingUp program.

Created using Cartes du Ciel (Sky Charts).

Created using Cartes du Ciel (Sky Charts).