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How big is Enif?

240,000,000 kilometers!

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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

Scale of the Universe > Enif
Distance from Earth to the Sun
During the day, the Sun doesn't seem so far away. It's actually about 150 million kilometers away. That distance is an astronomical unit, which is called an AU for short.
Rigel
Rigel is a blazing blue star, and the brightest star in the constellation of Orion. It lies near the equator, so it is visible from almost anywhere on Earth. Also, don't call it "wriggle" because it's pronounced like "rye-jel".
Gacrux
Gacrux can be found in the constellation Crux. Crux, which means "cross" in Latin, is known as the Southern Cross. We think Gacrux might be a binary star, but we haven't been able to spot its companion yet. The main star is a red giant.
Deneb
Deneb is the brightest star in the constellation of Cygnus. Deneb is 2,600 light-years away, which makes it the most distant of the 25 brightest stars. If you lived on Mars, Deneb would appear above the North Pole - not Polaris.
R Doradus
R Doradus is relatively large and is only 200 light-years from Earth, so its apparent size is the second largest in the sky! It is 0.05 arcseconds across. The Sun is the largest, at 1,920 arcseconds - 40,000 times larger.
Pistol Star
The Pistol Star is one of the most luminous stars known. In twenty seconds, it radiates as much energy as the Sun does in a year. Interstellar dust prevents us from seeing it. It's called the Pistol Star not because of its luminosity, but because it's in the Pistol Nebula.

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