How big is Vega?

Vega is one of the brightest stars in the northern sky, in the constellation Lyra, about 25 light-years from Earth, where a light-year is the distance light travels in one year. It spins so fast that it bulges at its equator. It is about 3.8 million kilometers (2.4 million miles) across at its equator, about 2.7 times the width of the Sun, and about 3.4 million kilometers from pole to pole.

Size

A star has no solid surface, so its size is the width of the glowing layer that its light comes from. Vega's shape was measured with the CHARA Array, which combines the light from several telescopes to see detail too fine for any one of them. Seen from Earth, Vega is almost exactly pole-on: one of its poles points nearly straight at Earth. So its outline looks round, and its width on the sky is its width at the equator.

A 2012 study fitted a model of a spinning star to the CHARA measurements. It found a radius at the equator of 2.73 times the Sun's and at the poles of 2.42 times, so the star is about 13% wider across its equator than from pole to pole. An earlier CHARA study, in 2006, found radii of 2.78 and 2.26 times the Sun's, which would make the star about 3.9 million kilometers wide at the equator.

Size comparisons

• Vega is about 2.7 times as wide as the Sun across its equator.
• About 300 Earths side by side would stretch across its equator.
• Altair, another fast-spinning star, is about 2.8 million kilometers wide at its equator, so Vega is about one-third wider.
• Regulus, the next larger star in the explorer, is about 5.8 million kilometers wide at its equator, about 1.5 times the width of Vega.
• If the Sun were shrunk to the size of a basketball, Vega would be a ball about 65 centimeters (26 inches) across at its equator.

A fast spin seen from above

The lines in Vega's spectrum are narrow, which once suggested that it turns slowly. In 2006, interferometers showed that it actually spins fast, and only looks slow because Earth sees it from above a pole. Vega turns about once every 17 hours. The Sun takes about 25 days.

The spin makes Vega's poles hotter than its equator: about 9,800 degrees Celsius at the poles and 8,600 at the equator. Seeing a hot pole explained why Vega had seemed too bright for its type of star. That matters because astronomers use Vega as a standard for measuring the brightness of other stars.

A disk of dust

In 1984, NASA's IRAS satellite found that Vega gives off extra infrared light, coming from warm dust around it. It was the first evidence of material orbiting a star other than the Sun. In 2024, the Hubble and James Webb space telescopes looked at the disk in new detail. It is nearly 160 billion kilometers across, more than 40,000 times the width of Vega.

The disk turned out to be very smooth, with no sign of large planets in wide orbits. Its only feature is a faint gap about twice as far from Vega as Neptune is from the Sun.

Sources

• Resolving Vega and the inclination controversy with CHARA/MIRC. Monnier et al., The Astrophysical Journal Letters, 2012.
• First Results from the CHARA Array VII: Long-Baseline Interferometric Measurements of Vega Consistent with a Pole-On, Rapidly Rotating Star. Aufdenberg et al., The Astrophysical Journal, 2006.
• Vega is a rapidly rotating star. Peterson et al., Nature, 2006.
• NASA's Hubble, Webb Probe Surprisingly Smooth Disk Around Vega. NASA, 2024.
• Imaging the Surface of Altair. Monnier et al., Science, 2007.
• First Results from the CHARA Array. I. An Interferometric and Spectroscopic Study of the Fast Rotator alpha Leonis (Regulus). McAlister et al., The Astrophysical Journal, 2005.
• Sun Fact Sheet. NASA, 2024.
• Earth Fact Sheet. NASA, 2024.
• Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.