| Object type | Main-belt asteroid, S-type (stony)[1] |
|---|---|
| Discovered | April 20, 1904 by Max Wolf, Heidelberg; first catalogued as 1904 NY[2] |
| Name origin | Unknown — perhaps a feminine form of Hercules[2] |
| Diameter | ≈ 168 km (JPL); often quoted near 200 km[1] |
| Shape | Blocky; axis ratios ≈ 1 : 1.1 : 1.3 (2002 model)[2] |
| Geometric albedo | ≈ 0.29 — bright for its size[1] |
| Rotation period | ≈ 9.4 hours[1] |
| Distance from Sun | 2.27–3.27 AU[1] |
| Orbital period | ≈ 4.6 years[1] |
| Inclination | ≈ 16.3°[1] |
| Moons | None confirmed; a 1978 report was not borne out by Hubble in 1993[2] |
One of Max Wolf’s photographic finds
Herculina was discovered on April 20, 1904 by Max Wolf at Heidelberg and first catalogued as 1904 NY.[2] Wolf was a pioneer of astrophotography and directed the Heidelberg-Königstuhl observatory from 1902 until his death in 1932.[3]
Nobody knows where the name came from. It may be a feminine form of Hercules, as all asteroid names were feminine then, or honour an unknown woman. Many of Wolf’s finds from this period were named after opera characters, but no such source is recorded for Herculina.[2]
The moon that wasn’t
In 1978, Herculina passed in front of the star SAO 120774. Anomalous dips in the starlight led to the claim of a satellite about 45 km across orbiting some 1,000 km away, making Herculina the first asteroid “confirmed” to have a moon.[2]
The claim did not hold. A careful search with the Hubble Space Telescope in 1993 failed to find any companion.[2] The first asteroid moon actually imaged was Dactyl, around Ida, seen by the Galileo spacecraft in 1993.[4]
Twenty years of arguing about its shape
Herculina’s light curves are complex, which made its shape surprisingly hard to work out. Speckle interferometry in 1982 suggested a three-axis body roughly 260 × 220 × 215 km. A 1987 study argued instead for a sphere with two dark spots, but a 1988 thermal study showed it could not be spherical.[2]
A 2002 model from photometry described a blocky, battered shape that “resembles a toaster”, with several large craters like those on 253 Mathilde and no major brightness variations across the surface.[2]
Orbit
Herculina travels between about 2.27 and 3.27 AU from the Sun, completing an orbit every 4.6 years, inclined about 16° to the ecliptic.[1] With a geometric albedo near 0.29 it reflects more light than most large asteroids, which are often much darker.[1]
How big is it really?
JPL lists a diameter of about 168 km, while other estimates put it nearer 200 km. It is believed to rank among the 20 largest main-belt asteroids, and its estimated mass would put it close to the top ten.[1][2]
Upgrading your telescope for asteroid hunting
Finding an asteroid is mostly about finding the right star field. A good finder, a wide-field eyepiece and a chart matter more than raw magnification. Our telescope accessory picker suggests upgrades by budget, sky and target.
Read more
Herculina’s phantom moon
How a 1978 stellar occultation produced the first “confirmed” asteroid moon — and why Hubble could not find it.
Read →Why Herculina has been called a toaster
A short history of models of Herculina’s shape, from speckle interferometry to the 2002 “battered cuboid”.
Read →Max Wolf and the photographic hunt for asteroids
How a Heidelberg astronomer turned the camera into the main tool for discovering asteroids, Herculina among them.
Read →Sources
- Small-Body Database Lookup: 532 Herculina — NASA JPL Solar System Dynamics
- 532 Herculina — Wikipedia
- Max Wolf — Wikipedia
- Dactyl (moon) — Wikipedia
- Occultation — Wikipedia
- Hubble Space Telescope — Wikipedia
- Auguste Charlois — Wikipedia
- Planetary Fact Sheet (orbit comparison) — NASA NSSDCA
Figures are rounded; where sources differ we note it. Spotted an error? Tell us.