Description: In the late 1990s, measurements of the light emitted from Type Ia supernovae (a class of exploding star), located in very distant galaxies showed that they appeared fainter than expected for a universe with a constant rate (speed) of expansion. The measurements were consistent with the scenario for a universe where the rate of expansion was accelerating. The cause for the accelerated expansion is attributed to dark energy, the nature of which is still unknown and a topic of current research. The accelerated expansion is occurring on very large scales and has no significant effect in individual gravitationally bound galaxies.

Related Terms:

• Cosmic Microwave Background (CMB)
• Cosmology
• Galaxy
• Supernova
• Universe

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

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