How big is Enif?

Enif is a supergiant star in the constellation Pegasus, the Winged Horse. It is about 240 million kilometers across, roughly 170 times the width of the Sun. That is an estimate of the width of its visible surface, worked out from how wide the star looks and how far away it is.

Size

Stars have no solid surface, so their sizes are worked out rather than measured directly. Between 1996 and 2003, astronomers measured Enif's apparent width several times with interferometers, which combine the light from several telescopes. The results cluster around 7.5 thousandths of an arcsecond, where an arcsecond is 1/3,600 of a degree. That is about the width of a human hair seen from 2.7 kilometers (1.7 miles) away.

The Hipparcos space mission measured Enif's distance as about 690 light-years. A light-year is the distance light travels in one year. At that distance, an apparent width of 7.5 thousandths of an arcsecond means a star about 237 million kilometers across. Allowing for the uncertainties in both measurements, Enif is between about 220 and 260 million kilometers across.

Size comparisons

• Enif is about 170 times as wide as the Sun, which is about 1.39 million kilometers across.
• If Enif took the Sun's place, its surface would reach past the orbit of Venus, about four-fifths of the way to the orbit of Earth.
• The supergiant Deneb, one of Enif's neighbors in the explorer, is about 1.2 times as wide as Enif, if Deneb's larger size estimate is right.
• The red giant R Doradus, one of Enif's larger neighbors in the explorer, is about 1.75 times as wide as Enif.
• If the Sun were shrunk to the size of a basketball, Earth would be a 2-millimeter bead 26 meters away, and Enif would be a ball about 41 meters (134 feet) across, more than a third of the length of a football field.

A future supernova

Enif has about 12 times the Sun's mass. Astronomers count it among the stars expected to end their lives as supernovae, the explosions of massive stars when their cores collapse. A 2020 study listed 31 such stars within about 3,300 light-years of Earth. Enif was the sixth nearest of them, closer than both Betelgeuse and Rigel.

In the hours before a nearby star's core collapses, detectors on Earth should record particles called neutrinos coming from the star. The 2020 study examined how well those detectors could point back to the star, and so tell astronomers which one on the list was about to explode.

Sources

• JMMC Measured Stellar Diameters Catalogue (II/345). Jean-Marie Mariotti Center, CDS VizieR, 2016.
• Presupernova neutrinos: directional sensitivity and prospects for progenitor identification. Mukhopadhyay et al., The Astrophysical Journal, 2020.
• Halo Photometry and Asteroseismology for 98 of the Brightest Stars Observed by TESS. Rudrasingam et al., Monthly Notices of the Royal Astronomical Society, 2026.
• IAU Catalog of Star Names. IAU Working Group on Star Names, 2022.
• The Constellations. International Astronomical Union.
• Measuring the Universe. International Astronomical Union.
• Quantitative spectroscopy of Deneb. Schiller and Przybilla, Astronomy & Astrophysics, 2008.
• One month convection timescale on the surface of a giant evolved star. Vlemmings et al., Nature, 2024.
• Astronomers track bubbles on star's surface in most detailed video yet. European Southern Observatory, 2024.
• Sun Fact Sheet. NASA, 2024.
• Venus Fact Sheet. NASA, 2024.
• Earth Fact Sheet. NASA, 2024.
• Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.
• 2026 NFL Rulebook. National Football League, 2026.
• Just How Small Is "Nano"?. National Nanotechnology Initiative.