Light transit time
The transit time of light is the time it takes for the light to travel a certain distance . Since the speed of light is finite and the same everywhere in the universe , the time of flight is synonymous with a distance that light traverses in this time.
Light transit times play a major role in astronomical dimensions. The light travel time from the sun to the earth is about 8 minutes and 20 seconds. The time it takes for light to travel from the moon to the earth is around 1.3 seconds. The distance from the earth to the moon can be measured, for example, by determining the time it takes for a laser pulse to travel from the earth to the moon and back (about 2.6 seconds). Suitable reflectors for such experiments (→ Lunar Laser Ranging ) are located on the lunar surface .
The astronomical distance specification light year is, strictly speaking, a time of flight. The Andromeda Galaxy , about 2.5 million light years away, has a light transit time of these 2.5 million years to Earth.
The time of flight must also be taken into account for satellite communication. With GPS ( Global Positioning System ), for example, the time of flight is used to determine the exact position.
With the remote control of robotic probes on our neighboring planet Mars , the light travel time from Earth to Mars of 3 minutes at best means that the probe can hardly be controlled interactively, since the probe's camera signal only shows the reaction to a control command after 6 minutes at the earliest.
The time-of-flight effect is when periodic signals arrive later on earth due to a change in location due to Kepler's laws . These signals must be of a strictly periodic nature, as in the case of pulsars , eclipsing variables and pulsating variables . Due to the time of flight effect, the first exoplanets around the pulsar PSR 1257 + 12 and a third companion C at the eclipse variable Algol have been found. However, some discoveries of invisible bodies due to the time-of-flight effect turned out to be inaccuracies in the periodic signals, such as the discovery of planets around cataclysmic variables .
Individual evidence
- ↑ SK Kozlowski, M. Konacki, P. Sybilski: Radio Pulsar Style Timing of Eclipsing Binary Stars from the ASAS Catalog . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1204.3836v1 .
- ^ A. Wolszczan & DA Frail: A planetary system around the millisecond pulsar PSR1257 + 12 . In: Nature . tape 355 , 1992, pp. 145-147 .
- ↑ Jonathan Horner, Robert A Wittenmyer, Jonathan P Marshall, Chris G Tinney and Oliver W Butters: The Curious Case of HU Aquarii - Dynamically Testing Proposed Planetary Systems . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1201.5730v1 .