How Big Is the Biggest Star?
The short answer
About 1,400 times wider than the Sun. That's VY Canis Majoris, one of the biggest stars we know. Put it where the Sun is and its surface would reach past Jupiter, with Mercury, Venus, Earth and Mars all inside it. Saturn would be the first planet still outside.
For scale, our Sun is 109 Earths wide. Sirius is almost twice as wide as the Sun, Arcturus about 25 times, Rigel about 80 and Betelgeuse, the red star on Orion's shoulder, about 750. If VY Canis Majoris filled your phone screen edge to edge, the Sun would be about one pixel.
Why past Jupiter but not Saturn
The standard measured value puts VY Canis Majoris at 1,420 times the Sun's radius, give or take 120. That radius is about 6.6 times the distance from Earth to the Sun. Jupiter orbits at 5.2 times that distance and Saturn at about 9.6. So the star's surface would land between the two.
That holds even at the small end of the estimate. To reach Saturn, the star would need to be more than about 1,950 times the Sun's radius.
All puff
VY Canis Majoris holds roughly 17 Suns' worth of material, give or take 8. Spread through a ball that big, the average comes out about 146,000 times thinner than air at sea level. Across the measured ranges for its size and mass, the answer runs from about 76,000 to 350,000 times thinner. ESO gives a higher mass, 30 to 40 Suns. That makes it about 62,000 to 83,000 times thinner, and about 48,000 at the extreme. The film says a hundred thousand, which sits in the middle.
That is an average. The gas is densest near the center and thinnest at the edge. The surface is still about 3,490 K, roughly 3,200 °C. Lava from Kīlauea in Hawaii erupts at about 1,170 °C, so the star's surface is hot enough to melt rock.
Is it the very biggest?
Nobody knows for sure. ESO puts WOH G64, a red supergiant in the Large Magellanic Cloud, at roughly 2,000 times the Sun's size. At least one other star has been put forward too. Their sizes are less certain than the measurement for VY Canis Majoris. That is why the film calls it one of the biggest stars we know, not the biggest.
Key numbers
| What | Number | Source |
|---|---|---|
| Width of the Sun | 109 Earths | NASA Space Place |
| Radius of Sirius A | 1.713 times the Sun's | Davis et al. 2011 |
| Radius of Arcturus | about 25.4 times the Sun's | Wikipedia, Solar radius |
| Radius of Rigel | about 79 times the Sun's (estimates vary) | Moravveji et al. 2012, summary by Emergent Mind |
| Radius of Betelgeuse | about 764 times the Sun's | Joyce et al. 2020 |
| Radius of VY Canis Majoris | about 1,420 times the Sun's, give or take 120 | Wittkowski et al. 2012 |
| Mass of VY Canis Majoris | about 17 Suns, give or take 8 | Wittkowski et al. 2012 |
| Surface temperature of VY Canis Majoris | about 3,490 K (about 3,200 °C) | Wittkowski et al. 2012 |
| Where its surface would sit in our solar system | about 6.6 times the Earth to Sun distance (Jupiter 5.2, Saturn 9.6) | Our arithmetic from Wittkowski et al. 2012 and NASA Planetary Fact Sheet |
| Average density compared with air at sea level | about 146,000 times thinner (48,000 to 350,000 across published estimates) | Our arithmetic from Wittkowski et al. 2012, ESO eso1546 and US Standard Atmosphere, 1976 |
| The Sun's width if VY Canis Majoris fills a phone screen | about 0.76 pixel on a screen 1,080 pixels wide; about 1 pixel on one 1,440 pixels wide | Our arithmetic from Wittkowski et al. 2012 and Samsung, Galaxy S25 Ultra screen |
| Size of WOH G64, a bigger candidate | roughly 2,000 times the Sun's | ESO eso2417, 2024 |
What the film simplifies
- The film rounds VY Canis Majoris to 1,400 times the Sun's width. The measured figure is about 1,420, give or take 120, and the authors say it may be on the high side.
- One pixel depends on your phone. On a screen 1,080 pixels wide the Sun comes out at about three quarters of a pixel. On a screen 1,440 pixels wide it is about one.
- The Sun is not a small star. About 75% of the stars in the Milky Way are red dwarfs, smaller than the Sun. It only looks tiny next to the giants.
- Saturn, you're fine. Probably. Saturn would sit outside the star's surface, but that close to so bright a star it would still roast.
- The planets are drawn glowing inside the star, and the bucket of star gas glows. Gas this thin would be almost see through. The glow stands for the heat.
- The faces, the Sun's stretching arm, the selfies and the bucket are cartoon.
At a glance
Runtime 1 minute 4 seconds · Topics: Stars, Star sizes, Red supergiants, Scale · Captions on YouTube · Full script below
Test yourself
Placed where the Sun is, the surface of VY Canis Majoris would sit about 6.6 times the Earth to Sun distance out. Jupiter orbits at 5.2 and Saturn at about 9.6. Which planets would end up inside the star?
Answer
Mercury, Venus, Earth, Mars and Jupiter. Saturn would be the first planet still outside.
A phone screen is 1,080 pixels wide and VY Canis Majoris fills it edge to edge. The star is about 1,420 times as wide as the Sun. How wide is the Sun on that screen?
Answer
1,080 divided by 1,420 is about 0.76, so the Sun is a little under one pixel wide.
VY Canis Majoris is about 1,420 times wider than the Sun but holds only about 17 Suns' worth of material. Why does that make it thinner than air on average?
Answer
Volume grows with the cube of the width, so the star has roughly 1,420 × 1,420 × 1,420, nearly 3 billion, times the Sun's volume. Spreading 17 Suns of material through all that space leaves it about 146,000 times thinner than air on average.
The script
Host: Our Sun is 109 Earths wide. He thinks that's huge.
Rocket: Cute selfie. Now take one with my buddy.
Host: Sirius, almost twice as wide.
Host: Arcturus, 25.
Host: Rigel, about 80.
Host: Meet Betelgeuse, the red star on Orion's shoulder.
Host: About 750.
Rocket: You're gonna need a longer arm.
Rocket: Wait. Which one's you?
Rocket: Hang on. I've got a bigger buddy!
Host: This is VY Canis Majoris, one of the biggest stars we know. About 1,400 times wider than the Sun.
Host: If it fills your screen edge to edge, the Sun is just one pixel.
Rocket: Ha! You're a dead pixel!
Host: Now put it where the Sun is.
Host: Its surface would reach past Earth. Past Mars. Past Jupiter.
Rocket: Saturn, you're fine. Probably.
Host: But it's all puff.
Rocket: Watch this.
Host: On average, it's about a hundred thousand times thinner than the air you breathe.
Host: And still hot enough to melt rock.
Rocket: Ow! Hot air! Remind you of anyone?
Rocket: Hey! Size doesn't work like that!
Sources
- The Sun is 109 times wider than Earth.NASA Space Place
- Radius ratio of the Sun to Earth is 109.2.NASA Sun Fact Sheet
- Sirius A is 1.713 times the Sun's radius, from its measured angular diameter.Davis et al. 2011
- Arcturus is about 25.4 times the Sun's radius.Wikipedia, Solar radius
- Rigel is about 79 times the Sun's radius.Moravveji et al. 2012, summary by Emergent Mind
- Betelgeuse is about 764 times the Sun's radius.Joyce et al. 2020
- Betelgeuse is a red supergiant at the shoulder of Orion, about 724 times the Sun's radius.NASA Watch the Skies, 2024
- VY Canis Majoris is about 1,420 times the Sun's radius, give or take 120, with a mass of about 17 Suns and a surface temperature of about 3,490 K.Wittkowski et al. 2012
- VY Canis Majoris is one of the largest known stars in the Milky Way, would encompass the orbit of Jupiter, and has 30 to 40 times the Sun's mass.ESO eso1546
- Orbital distances of Earth, Jupiter and Saturn.NASA Planetary Fact Sheet
- Air at sea level has a density of 1.225 kg per cubic meter.US Standard Atmosphere, 1976
- Kīlauea lava erupts at about 1,170 °C.USGS, How hot is a Hawaiian volcano
- WOH G64, a red supergiant in the Large Magellanic Cloud, is roughly 2,000 times the Sun's size.ESO eso2417, 2024
- Some large phones have screens 1,440 pixels wide.Samsung, Galaxy S25 Ultra screen
- About 75% of Milky Way stars are red dwarfs, smaller than the Sun.NASA, Types of stars