Astronomers Heinrich Louis d’Arrest & Johann Gottfried searched for the planet Neptune #OnThisDay 1846 on a letter received at the Berlin Observatory that morning from French mathematician Urbain Jean-Joseph Le Verrier, and found the distant ice giant just after midnight, September 24th.

The search was conducted with a 9" refractor, and found on the Aquarius/Capricornus border. Neptune was the 1st planet discovered using math. In 2024, +8th mag Neptune is now in Pisces and just passed opposition on September 21st, having completed one 165-year orbit (since discovery) in 2011.