Description: A standard candle is an astronomical object whose luminosity (energy emitted per unit time) is known and can be used to estimate the distance from the object to the Earth.

For most celestial objects, astronomers do not have information about their distance from Earth. Under those circumstances, it can be difficult to decide whether one is looking at a distant, but very bright object, or a closer and less bright object – the apparent brightness, as measured from Earth, can be the same in both cases. Standard candles have luminosities that can be estimated without knowing their distance. The standard candle's distance can then be calculated by comparing that luminosity and the object's apparent brightness in the night sky. Important examples include Cepheid variables (pulsating stars where there is a relation between the pulsation period and the luminosity), and Type Ia supernovae (bright stellar explosions where there is a relation between the maximum luminosity and the timescale on which the brightness decreases directly afterwards).

Related Terms:

• Absolute Magnitude
• Apparent Magnitude
• Cepheid Variable
• Luminosity
• Supernova
• Distance Ladder

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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