Yellow, white or green: What colour is the Sun?

The 4.5-billion-year-old star appears to change hue throughout the day

An image of the Sun captured by the Solar Orbiter spacecraft on May 18, 2022. Photo: European Space Agency
Powered by automated translation

Sometimes the Sun appears yellow, in the evenings it seems red, it is white for astronauts in space and billionaire Elon Musk thinks it is green. But what colour is it, really?

The star that helps keeps the Earth warm actually gives off light that spans many different hues, so it is not one particular colour.

Scientists told The National that the Sun appears to us in different shades because of how its light scatters in Earth’s atmosphere.

“What we perceive as colour is radiation within a narrow wavelength range,” said Dr Dimitra Atri, an astrophysicist at the New York University Abu Dhabi.

“The Sun emits radiation across all wavelengths, making it a blend of colours and appearing white. It is the whitest object that we see.

“However, due to the scattering of light in the atmosphere, it appears yellowish.”

What is the Sun made of?

All of the planets in our solar system orbit the Sun, so its gravity is what keeps everything together.

It is a 4.5-billion-year-old star made up of hydrogen and helium.

Earth is habitable because it sits at a perfect distance from the Sun at about 150 million km – not too close and not too far.

But our planet does get hit by intense solar flares – eruption of electromagnetic radiation from the Sun – every now and then, causing radio blackouts, power outages and damage to spacecraft in Earth's orbit.

Why does it appear in different colours?

Dr Atri said that it appears redder in the morning and evenings because sunlight has to travel through more of the atmosphere, which contains dust and pollution at lower altitudes.

“This atmospheric scattering is also why the Sun appears whiter when observed from airplanes, as there is less obstruction, and astronauts perceive it the same way from outer space as they have an unobstructed view of the sun,” he said.

Dr Sarah Gallagher, director of the Institute for Earth and Space Exploration at Western University in Canada, also said that the colour of the Sun is perceived by humans depending on how our eyes and brains capture and interpret light.

It also depends on what we are looking through when we look at the Sun – for example, how much of the Earth's atmosphere.

"On Earth, we are looking at the Sun through our atmosphere, which tends to scatter out the higher energies (shorter wavelengths) of light – the purples and blues," she said.

"This is what makes the sky blue (the light doesn’t disappear, it just gets relocated), and the Sun looks yellow because the blue light has been taken out, and so it shifts the weight of the light reaching our eyes towards the red end of the rainbow.

"This becomes even more obvious during sunrises and sunsets, when the Sun’s light passes through more of the atmosphere, and so the Sun looks orange or red."

SpaceX and Tesla founder Elon Musk sparked a debate in December when he tweeted that the Sun was green.

"A nice trick question is what colour is the sun? It appears white in space, but, as measured by peak photon count, it is green," he said.

Will the Sun keep Earth warm forever?

While the Sun is what keeps the solar system intact, it is not going to "live" forever.

Dr Atri said that Sun will eventually diminish in size and turn into a white dwarf star.

"In approximately five billion years, the Sun will undergo expansion and transform into a red giant, engulfing Mercury and Venus," he said.

"As a consequence, Earth will no longer be habitable.

"Some estimates even propose that our planet will eventually be consumed by the Sun. In that case, we might need to relocate elsewhere, maybe Titan, which could be a viable option.

"Once the Sun exhausts most of its fuel, it will diminish in size and evolve into a white dwarf star."

Dr Gallagher said this was not "an urgent problem".

"Five billion years is a very long time though – it is approximately the current age of the Earth, and longer than there has been life on Earth," she said.

"Eventually, in about five billion years, the Sun will experience a much more dramatic transition as it runs out of hydrogen in its core and turns into a red giant star.

"At that point, it will expand and grow much brighter and cooler. It will grow so much that the Sun’s surface will extend to the Earth’s orbit, and the Earth will be swallowed by the Sun."

Updated: July 08, 2023, 2:30 AM