Footsteps of Celestial Police

A binocular activity

Eighteenth-century astronomers felt there was something wrong with our solar system. They suspected that an unknown planet existed, moving between the orbits of Mars and Jupiter at 2.8 Astronomical Units from the sun. A curious mathematical relationship eventually called the Bode–Titus Law (BT), had been formulated which seemed to satisfactorily describe the relative spacing of the planetary orbits. A planet was predicted orbiting 2.8 AU from the sun, but nothing was seen.


 Planetary Spacing Table

Planet   B–T value                     Actual value     
Mercury 0.40 AU 0.39 AU
Venus 0.70 0.72
Earth 1.00  1.00
Mars 1.60 1.52
?    2.80 ---
Jupiter 5.20 5.20
Saturn 10.0 9.54
Uranus 19.6 19.19

Neptune was not known at the time

European astronomers felt strongly enough about the reality of this unknown planet that they formed a team, nicknamed the “Celestial Police,” to search for it. However, a new body was spotted shortly before they could begin their organized search. On the night of January 1, 1801, team member Guiseppe Piazzi spied a starlike object that had moved slightly in the heavens near the Hyades and Pleiades star clusters. It was soon realized that it was a small body located near the same distance from the sun as was the “missing” planet predicted by the Bode-Titus law. It was eventually called Ceres.

Three other small bodies were discovered over the next few years, all lying about the same distance from the sun as Ceres. They were soon named Pallas, Juno, and Vesta. Over the years, many thousands of these small planetoids were found. They became known as asteroids.

Within the past twenty years, Ceres has been reclassified as a “dwarf planet.” The rest, including Pallas, Juno, and Vesta, are still referred to as asteroids.


 Binocular Program: Tracking the asteroid 4 Vesta in its orbital path

 How to find Vesta (4 Vesta will appear starlike, even through a telescope. It will not be bright, but binoculars should reveal it.)

  1. Look for the bright stars Arcturus and Spica in the eastern half of the sky. They belong the "Spring Triangle" with the third member, Denebola, lying to their west. See Map A.
  2. Denebola is the easternmost star of Leo, Just to its west are two moderately bright stars, Delta and Theta Leonis.
  3. Vesta lies to their west about 1 binocular field. See Map B.
  4. Triangulate among 60 Leonis, 51 Leonis and Vesta, all easily seen in binoculars.
  5. Vesta will be slightly dimmer than 51 Leonis.
  6. Vesta will be closest 51 Leonis on April 17. Both will easily lie in the same telescope field of view.

 Click on the image to print/view PDF

Map A - Vesta 2021

Map B - Vesta 2021



  • 4 Vesta is 325 miles (525 km) in diameter (15% that of our moon).
  • At the beginning of April, it lies 133 million miles (212 million km) from Earth; in the middle of the month, it is 142 million miles (228 million km); and at the end of the month, it moves farther away to 154 million miles (247 million km).