Brightest From Earth
Only Vesta regularly attains a brightness sufficient to be visible to the naked eye. The following asteroids can all reach an apparent magnitude brighter than or equal to the +8.3 attained by Saturn's moon Titan at its brightest, which was discovered 145 years before the first asteroid was found owing to its closeness to the easily observed Saturn.
None of the asteroids in the outer part of the asteroid belt can ever attain this brightness. Even Hygiea and Interamnia rarely reach magnitudes of above 10.0. This is due to the different distribution of spectral types within different sections of the asteroid belt being such that the highest-albedo asteroids are all concentrated closer to Mars, and much lower albedo C and D types being common in the outer belt.
Those asteroids with very high eccentricities will only reach their maximum magnitude on unusual occasions when their perihelion is very close to a heliocentric conjunction with Earth, or (in the case of 99942 Apophis) when the asteroid passes very close to the Earth.
| Asteroid | Magnitude when brightest |
Mean Distance from Sun (in AU) |
Eccentricity of orbit |
Diameter (km) |
Year of discovery |
|---|---|---|---|---|---|
| 99942 Apophis | 3.4* | 0.922 | 0.191 | 0.27 | 2004 |
| 4 Vesta | 5.20 | 2.361 | 0.089172 | 529 | 1807 |
| 2 Pallas | 6.49 | 2.773 | 0.230725 | 544 | 1802 |
| 1 Ceres | 6.65 | 2.766 | 0.079905 | 952 | 1801 |
| 7 Iris | 6.73 | 2.385 | 0.231422 | 200 | 1847 |
| 433 Eros | 6.8 | 1.458 | 0.222725 | 34 × 11 × 11 | 1898 |
| 6 Hebe | 7.5 | 2.425 | 0.201726 | 186 | 1847 |
| 3 Juno | 7.5 | 2.668 | 0.258194 | 233 | 1804 |
| 18 Melpomene | 7.5 | 2.296 | 0.218708 | 141 | 1852 |
| 15 Eunomia | 7.9 | 2.643 | 0.187181 | 268 | 1851 |
| 8 Flora | 7.9 | 2.202 | 0.156207 | 128 | 1847 |
| 324 Bamberga | 8.0 | 2.682 | 0.338252 | 229 | 1892 |
| 1036 Ganymed | 8.1 | 2.6657 | 0.533710 | 32 | 1924 |
| 9 Metis | 8.1 | 2.387 | 0.121441 | 190 | 1848 |
| 192 Nausikaa | 8.2 | 2.404 | 0.246216 | 103 | 1879 |
| 20 Massalia | 8.3 | 2.409 | 0.142880 | 145 | 1852 |
Read more about this topic: List Of Notable Asteroids
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