NASA measures planets using a variety of techniques, focusing primarily on distance and size.
Measuring Distance
The primary method for measuring distances within our solar system uses the astronomical unit (AU).
- What is an AU? The AU is defined by the mean distance between the Earth and the Sun, which is about 150 million kilometers (93 million miles).
- How was the AU determined? The precise value of the AU was refined by NASA’s Deep Space Network in the 1960s using radar echoes from Venus. This involved sending radar signals to Venus and then measuring how long it took for the signals to return, enabling an accurate distance calculation.
| Unit of Measurement | Basis | Use |
|---|---|---|
| Astronomical Unit (AU) | Mean distance from Sun to Earth (150,000,000 km) | Measuring distances within the solar system |
Other Measurement Techniques
While the AU is the standard for distance within the solar system, other methods are also used:
- Radar: Used for relatively nearby objects, such as Venus, as described above.
- Parallax: For nearby stars, this method measures the apparent shift in a star's position against a distant background.
- Doppler shift: The way waves change when a source is moving to or from you. NASA uses this principle for distance and speed for celestial bodies.
Measuring Size
Measuring the size of planets involves:
- Angular Diameter: Measuring the planet's angle in the sky and using the calculated distance to determine its actual size.
- Observations from Space: Telescopes and probes in space offer more precise measurements, free from atmospheric interference.
Practical Insights
- NASA often uses a combination of techniques to cross-validate the measurements and ensure high accuracy.
- Space missions provide valuable data for more refined calculations of distance and size.
