Scientists use various methods based on the properties of light to measure distances on Earth and in space. Here are some common techniques:
Triangulation/Parallax: This method is used to measure relatively close distances, such as within our solar system. It involves observing an object from different positions and measuring the apparent shift in its position against background objects. By knowing the baseline (distance between the observer positions) and the angle of the observed shift, scientists can calculate the distance using trigonometry.
Radar Ranging: Radar (radio detection and ranging) uses radio waves to measure distances. A radar transmitter emits radio waves towards an object, and the reflected waves are detected. By measuring the time it takes for the radio waves to travel to the object and back, scientists can calculate the distance using the speed of light.
LIDAR (Light Detection and Ranging): LIDAR is similar to radar, but it uses light instead of radio waves. Pulses of laser light are emitted towards an object, and the reflected light is detected. By measuring the time taken for the light to travel to the object and back, scientists can calculate the distance using the speed of light. LIDAR is often used for mapping terrain, measuring atmospheric properties, and in remote sensing applications.
Cepheid Variables: In astronomy, certain types of stars called Cepheid variables exhibit a regular pulsation in brightness. The period of their brightness variations is directly related to their intrinsic brightness. By comparing the intrinsic brightness with their apparent brightness, scientists can determine their distances. This method is especially useful for measuring distances to galaxies and determining the scale of the universe.
Standard Candles: Certain astronomical objects, such as supernovae of a specific type (Type Ia supernovae), have a well-known intrinsic brightness. By measuring their apparent brightness, scientists can determine their distances. These objects serve as "standard candles" because their brightness-distance relationship is established through empirical observations.
Redshift: In cosmology, the expansion of the universe causes light from distant galaxies to be redshifted, meaning its wavelength is stretched towards longer wavelengths. By measuring the redshift of light from distant objects, scientists can determine their recession velocities and, in turn, their distances using Hubble's Law.
These are just a few examples of how light is used to measure distances on Earth and in space. Scientists employ a combination of techniques and rely on the properties of light to develop accurate distance measurements across various scales, from nearby objects to galaxies and beyond.