how bright is the Sun?

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Don’t be misled though.  How bright an object appears depends not only on its true brightness but also on how far away it is.

The Sun is the brightest star in our sky, but that’s because it’s also the closest star to us. Astronomers compare the true brightness of stars by calculating how they would look if viewed from a standard distance of 32.6 light years away.  If the Sun were viewed from this distance it would appear over 300 times fainter than Sirius (the brightest star in our nighttime sky) appears to us on Earth.

The Sun creates daylight on Earth. If you want to know how daylight compares to other forms of light on Earth, check out our Factory entry on illumination.

The Earth's atmosphere scatters the Sun's light and creates a bright sky, so it is difficult to see the stars in the daytime. Even so, planets can often be seen in the early morning or evening sky.

Venus, the brightest of the planets, can often be seen in broad daylight. It is very bright not because of its size - it is slightly smaller than Earth - but because it is close to us and has clouds that reflect almost 75% of the sunlight that falls on it.

We can't usually see stars in the daytime unless we use a telescope. Even then only the very brightest stars can be observed.

However, if we went out in space, we would be able to see the stars all the time, even close to the direction of the Sun. Here is a picture taken with SOHO-LASCO. In the centre is the Sun but it is blocked out by a disk so that we can see the light shining from the material streaming out from the Sun. The position and size of the Sun are marked by a white circle . The white dots sprinkled across the picture are stars . There’s a comet heading towards the Sun .

SOHO can see the stars and the Sun at the same time because it is out in space and so the Earth's atmosphere does not create the bright background which drowns the light of the stars.

Here is a movie made by SOHO - LASCO.   Can you see the stars and planets moving in the background?   Remember that SOHO is orbiting around the Sun and moving relative to the stars.
The true brightness of a star depends on two things: its temperature (or colour) and its size.   The temperature matters because the hotter a star's surface is, the more radiation it gives out in every square metre of its surface.   The size matters because the larger it is, the more square metres there are to radiate!

Sirius is the brightest star in the sky. It has a surface temperature of 10,000 °C and is a blue star. It is nine light years away, not particularly close. It is often called "the Dog star". It has a very faint companion, a white dwarf known as Sirius B, which is very dense. Sirius B has the mass of the Sun, but is only the size of the Earth!

what colour is the Sun? | how hot is the Sun?
how big is the Sun? | what's the mass of the Sun?

how old is the Sun | what is the Sun made of? | does the Sun rotate?