Brightest planet from Earth

The brightest planet as seen from Earth is Venus, which has an average V-band apparent magnitude of -4.14, making it the second-brightest object in the night sky after the Moon.

Apparent and absolute magnitudes are scales used in astronomy to quantify the brightness of celestial objects. Absolute magnitude is the intrinsic brightness of an object that does not vary with distance, while apparent magnitude is the brightness of an object as viewed from Earth.

The magnitude scale uses the star Vega as its zero-point, with dimmer objects being described using positive numbers and brighter objects being described using negative numbers. Owing to the enormous variability in the brightness of objects visible to astronomers, the scale is logarithmic. Each step on the scale represents the brightness increasing or decreasing by a factor of 2.512 relative to the previous step.

This means that an object with a magnitude (apparent or absolute) of 1 is only 39.8% as bright as an object with a magnitude of 0, and an object with a magnitude of 4 is only 2.5% as bright. Going the other way, an object with a magnitude of -1 is 251.2% brighter than an object with a magnitude of 0, and an object with a magnitude of -4 is 3,981% brighter.

Because what we think of as light represents a broad swath of frequencies on the electromagnetic spectrum, it is necessary to specify what frequency band is being referred to by a magnitude calculation. For general classification, astronomers use what is called V band (or Visual band) absolute magnitude – which corresponds to the brightness of an object at the peak sensitivity of the eye’s spectral response; in this case, it is in the green part of the spectrum at between 507 nanometres and 555 nanometres depending on day or night vision conditions.