3 ms·
> Relying upon high-powered terrestrial radars (of up to one MW[3]), radar astronomy is able to provide extremely accurate astrometric information on the struct
by Medox 6y ago
> Relying upon high-powered terrestrial radars (of up to one MW[3]), radar astronomy is able to provide extremely accurate astrometric information on the structure, composition and movement of Solar System objects.[4] This aids in forming long-term predictions of asteroid-Earth impacts, as illustrated by the object 99942 Apophis. In particular, optical observations measure where an object appears in the sky, but cannot measure the distance with great accuracy (relying on parallax becomes more difficult when objects are small or poorly illuminated). Radar, on the other hand, directly measures the distance to the object (and how fast it is changing). The combination of optical and radar observations normally allows the prediction of orbits at least decades, and sometimes centuries, into the future.
https://en.wikipedia.org/wiki/Radar_astronomy https://en.wikipedia.org/wiki/Radar_astronomy
- mturmon 6y agoIndeed, the fact that Mercury is not tidally-locked with the Sun was discovered using the Arecibo radar telescope. If I remember correctly, they used the Doppler shift imparted to the radio wave --which expresses differently across the width of the rotating planet -- to learn this. "The rotation of Mercury was not discovered until 1965. Until then the most widely accepted theory had Mercury tidal locked to the Sun. Soviet scientists bounced radar signals off the planet’s surface in 1962 verifying that the planet rotated, but it wasn’t until scientists using the Arecibo Observatory verified the planet’s sidereal rotational period of 58.647 day." (From: https://www.universetoday.com/14008/rotation-of-mercury/ https://www.universetoday.com/14008/rotation-of-mercury/)