# 249 Ilse

**249 Ilse** (provisional designation A885 QA) is a main-belt asteroid about 35 km in diameter, discovered on 16 August 1885 by C. H. F. Peters at Clinton, New York, and named after a legendary princess of the Harz mountains in Germany.<sup>[1](https://ndl.ethernet.edu.et/bitstream/123456789/32939/1/Lutz%20D.%20Schmadel.pdf)</sup>

| Key fact | Detail |
|---|---|
| Discovery | 16 August 1885 by C. H. F. Peters at Clinton, New York<sup>[1](https://ndl.ethernet.edu.et/bitstream/123456789/32939/1/Lutz%20D.%20Schmadel.pdf)</sup> |
| Name origin | Probably a legendary princess of the Harz mountains; also the name of a small river flowing from the Harz<sup>[1](https://ndl.ethernet.edu.et/bitstream/123456789/32939/1/Lutz%20D.%20Schmadel.pdf)</sup> |
| Size and albedo | Diameter 34.83 ± 1.1 km, geometric albedo 0.0428 ± 0.003 (IRAS survey)<sup>[2](https://irsa.ipac.caltech.edu/IRASdocs/surveys/PL-TR-92-2049.pdf)</sup> |
| Rotation | Synodic period 84.94 ± 0.01 hours, lightcurve amplitude 0.34 ± 0.02 magnitudes<sup>[3](https://mpbulletin.org/issues/MPB_42-3.pdf)</sup> |
| Orbit | Semi-major axis 2.378 AU, eccentricity 0.2172, inclination 9.62°, period 1,340 days (3.67 years)<sup>[4](https://www.spacereference.org/asteroid/249-ilse-a885-qa)</sup> |
| Hazard status | Not a near-Earth object and not classified as potentially hazardous; its orbit stays 0.87 AU from Earth's orbit at the closest point<sup>[4](https://www.spacereference.org/asteroid/249-ilse-a885-qa)</sup> |
| Observational record | 7,575 observations in the Minor Planet Center database, with astrometry dating back to 12 September 1885<sup>[4](https://www.spacereference.org/asteroid/249-ilse-a885-qa)</sup> |

## Discovery and naming

Peters found Ilse at the Clinton observatory in New York in August 1885, during the same year in which several other numbered asteroids ([247 Eukrate](https://www.edgepedia.org/247-eukrate), [248 Lameia](https://www.edgepedia.org/248-lameia), [250 Bettina](https://www.edgepedia.org/250-bettina)) were discovered in Europe.<sup>[1](https://ndl.ethernet.edu.et/bitstream/123456789/32939/1/Lutz%20D.%20Schmadel.pdf)</sup> According to the *Dictionary of Minor Planet Names*, the name was chosen probably after a legendary princess of the Harz mountains in Germany; Ilse is also the name of a small river flowing from the Harz.<sup>[1](https://ndl.ethernet.edu.et/bitstream/123456789/32939/1/Lutz%20D.%20Schmadel.pdf)</sup> The name is pronounced /ˈɪl.zə/.<sup>[5](https://space.fandom.com/wiki/Pronunciation_of_asteroid_names)</sup>

## Orbit

Ilse orbits the Sun in the main portion of the asteroid belt between Mars and Jupiter, with a semi-major axis of 2.378 AU, eccentricity 0.2172, and inclination 9.62°.<sup>[4](https://www.spacereference.org/asteroid/249-ilse-a885-qa)</sup> One orbit takes 1,340 days (3.67 years), carrying the asteroid from 1.86 AU at perihelion to 2.89 AU at aphelion, at an average orbital speed of 19.31 km/s.<sup>[4](https://www.spacereference.org/asteroid/249-ilse-a885-qa)</sup> Its closest approach to [Earth's orbit](https://www.edgepedia.org/earths-orbit) is 0.87 AU, and JPL orbital simulations show no close approaches to Earth; JPL has therefore not classified Ilse as potentially hazardous, and it is not considered a viable target for human exploration by the NHATS study.<sup>[4](https://www.spacereference.org/asteroid/249-ilse-a885-qa)</sup> Objects with similar orbits include [7 Iris](https://www.edgepedia.org/7-iris), 9 Metis, and [105 Artemis](https://www.edgepedia.org/105-artemis).<sup>[4](https://www.spacereference.org/asteroid/249-ilse-a885-qa)</sup>

## Physical characteristics

The IRAS Minor Planet Survey measured a mean diameter of 34.83 km with a one-sigma uncertainty of 1.1 km and a geometric albedo of 0.0428 ± 0.003, a dark surface reflecting about 4 percent of incident light.<sup>[2](https://irsa.ipac.caltech.edu/IRASdocs/surveys/PL-TR-92-2049.pdf)</sup> The asteroid's absolute magnitude is H = 11.33.<sup>[2](https://irsa.ipac.caltech.edu/IRASdocs/surveys/PL-TR-92-2049.pdf)</sup>

**Slow rotation.** Photometry at the Organ Mesa Observatory using a 35 cm telescope and more than 5,000 data points gave a synodic rotation period of 84.94 ± 0.01 hours with an amplitude of 0.34 ± 0.02 magnitudes.<sup>[3](https://mpbulletin.org/issues/MPB_42-3.pdf)</sup> At about 3.5 days per rotation, this is an unusually slow spin for a main-belt asteroid, and the sizable amplitude indicates a strongly elongated shape.<sup>[3](https://mpbulletin.org/issues/MPB_42-3.pdf)</sup> A convex shape model for Ilse exists in the DAMIT database, with a listed rotation period of 84.995 hours and spin-axis solutions at ecliptic coordinates (2°, 85°) and (222°, 41°).<sup>[6](https://astro.kretlow.de/cora/events/sodis/2023-04-25/UCAC4%20430-053659/%28249%29%20Ilse/)</sup>

## Occultations

Stellar occultations, in which the asteroid's shadow crosses Earth and briefly hides a background star, provide direct size measurements. A predicted event on 5 June 2013, computed by Steve Preston, would have carried the roughly 37 km asteroid across a narrow path over northern Australia, occulting an 11.8-magnitude star in [Corona Australis](https://www.edgepedia.org/corona-australis) for at most 4.3 seconds, with the shadow moving at 8.68 km/s.<sup>[7](https://www.occultations.org.nz/planet/2013/updates/130605_249_29817_u.htm)</sup>

An occultation on 25 April 2023 of the star UCAC4 430-053659 (Gaia magnitude G = 14.26) was successfully observed by two video observers, Roland Boninsegna and Simon Kidd, recording chords (straight-line measurements across the asteroid's shadow silhouette) of 36.7 km and 15.5 km lasting 4.96 and 2.10 seconds.<sup>[6](https://astro.kretlow.de/cora/events/sodis/2023-04-25/UCAC4%20430-053659/%28249%29%20Ilse/)</sup> A circular profile fit to the two chords gave a diameter of 40 km, consistent with the IRAS value within the uncertainties, and the predicted shadow speed was 7.4 km/s with an estimated maximum duration of 4.7 seconds.<sup>[6](https://astro.kretlow.de/cora/events/sodis/2023-04-25/UCAC4%20430-053659/%28249%29%20Ilse/)</sup>

## References

1. [Lutz D. Schmadel, Dictionary of Minor Planet Names, 5th ed. (entries for 247–250)](https://ndl.ethernet.edu.et/bitstream/123456789/32939/1/Lutz%20D.%20Schmadel.pdf)
2. [IRAS Minor Planet Survey, albedo and diameter table, IPAC/IRSA](https://irsa.ipac.caltech.edu/IRASdocs/surveys/PL-TR-92-2049.pdf)
3. [Frederick Pilcher (2015), "128 Nemesis, 249 Ilse, and 279 Thule," Minor Planet Bulletin 42 (3)](https://mpbulletin.org/issues/MPB_42-3.pdf)
4. [Asteroid Ilse (249 Ilse, A885 QA), Space Reference](https://www.spacereference.org/asteroid/249-ilse-a885-qa)
5. [Pronunciation of asteroid names, Space Wiki](https://space.fandom.com/wiki/Pronunciation_of_asteroid_names)
6. [2023-04-25 occultation of UCAC4 430-053659 by (249) Ilse, Collaborative Occultation Resources](https://astro.kretlow.de/cora/events/sodis/2023-04-25/UCAC4%20430-053659/%28249%29%20Ilse/)
7. [RASNZ Occultation Section, Ilse occultation update for 2013 June 5](https://www.occultations.org.nz/planet/2013/updates/130605_249_29817_u.htm)

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*Topic: Encyclopedia › Places and geography › Extraterrestrial places › Small bodies of the Solar System › Main-belt asteroids and numbered minor planets › Inner-belt asteroids › Asteroids named for mythological figures*

*Initially written Oct 21, 2026 · Edited: Oct 25, 2026*

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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license