| Minorplanet: | yes |
| 3905 Doppler | |
| Background: |
|
| Discovery Ref: |   |
| Discovered: | 28 August 1984 |
| Mpc Name: | (3905) Doppler |
| Alt Names: | 1984 QO |
| Named After: | Christian Doppler |
| Orbit Ref: |   |
| Epoch: | 4 September 2017 (JD 2458000.5) |
| Uncertainty: | 0 |
| Observation Arc: | 35.81 yr (13,078 days) |
| Perihelion: | 1.9001 AU |
| Semimajor: | 2.5596 AU |
| Eccentricity: | 0.2577 |
| Period: | 4.10 yr (1,496 days) |
| Mean Motion: | / day |
| Inclination: | 14.192° |
| Asc Node: | 343.32° |
| Arg Peri: | 90.823° |
| Satellites: | 1 |
| Dimensions: | km |
| Spectral Type: | S  |
| Abs Magnitude: | 12.6 |
3905 Doppler, provisional designation, is a stony asteroid and binary system from the middle region of the asteroid belt, approximately 8 kilometers in diameter.
The asteroid was discovered on 28 August 1984, by Czech astronomer Antonín Mrkos at Kleť Observatory and named after physicist Christian Doppler.
Doppler orbits the Sun in the central main-belt at a distance of 1.9–3.2 AU once every 4 years and 1 month (1,496 days). Its orbit has an eccentricity of 0.26 and an inclination of 14° with respect to the ecliptic. It has been characterized as a common S-type asteroid.
A minor-planet moon orbiting Doppler every 50.8 hours (or 2 days, 2 hours, and 48 minutes) was found orbiting the asteroid in 2013. This is fairly long orbital period for a moon of an asteroid of this size. The satellite's orbital period is identical to the primary's rotation period (F-type binary).
According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Doppler measures 8.021 kilometers in diameter and its surface has an albedo of 0.228, while the Collaborative Asteroid Lightcurve Link assumes a standard albedo for stony asteroids of 0.20 and calculates a diameter of 8.97 kilometers with an absolute magnitude of 12.6.
This minor planet was named after Christian Doppler (1803–1853), Austrian physicist in Vienna and well known for the Doppler effect, which he first described in 1842, in his book "Ueber das farbige Licht der Doppelsterne". The naming was proposed by Jana Tichá and M. Šolc. The approved naming citation was published by the Minor Planet Center on 28 August 1996 .