In space, where there is no absolute frame of reference, measuring speed can be challenging. However, there are still ways to determine relative velocities and measure speeds using different techniques. Here are a few methods commonly employed:
Doppler Shift: The Doppler effect is a change in frequency or wavelength of a wave (such as light or sound) observed when there is relative motion between the source of the wave and the observer. By analyzing the shift in frequency or wavelength, the relative speed between the source and the observer can be determined. This principle is utilized in measuring the speeds of objects in space, such as stars, galaxies, and spacecraft.
Radar and Lidar: Radar (Radio Detection and Ranging) and Lidar (Light Detection and Ranging) are techniques that use the reflection and timing of signals to determine the distance and relative velocity of objects. By emitting a signal and measuring the time it takes for the signal to bounce back, the speed of the object can be calculated. Radar and Lidar are commonly used in astronomy, atmospheric sciences, and space missions to measure the velocities of celestial bodies and spacecraft.
Stellar Parallax: Stellar parallax is a technique used to measure the distance to nearby stars and determine their relative motion. It relies on observing the apparent shift in the position of a star as seen from different points in Earth's orbit around the Sun. By measuring the angle of this shift, astronomers can calculate the relative velocity of the star.
Spacecraft Tracking: When spacecraft are sent into space, their trajectories can be tracked and monitored from Earth. By precisely measuring the position and time, scientists can calculate the spacecraft's speed and trajectory using mathematical models and principles of orbital mechanics.
It's important to note that while there is no absolute frame of reference in space, relative velocities and speeds can still be measured and calculated based on the observed effects and interactions between objects or by utilizing known physical principles and techniques.