The North Star, also known as Polaris, is often described as having a yellowish or whitish color. The actual apparent color of the star depends on a few different factors.
Quick Answer
The North Star appears white to the naked eye here on Earth. However, it is technically a yellow supergiant star with a surface temperature of around 6,000 Kelvin. This gives it a yellowish tint, but it is difficult to discern with the human eye alone.
What is the North Star?
The North Star, known scientifically as Polaris, is the current northern pole star. It sits almost directly above the Earth’s northern axis in the sky.
Polaris is a three-star system that includes a supergiant primary star along with two smaller companion stars. It is located about 430 light years from Earth in the constellation Ursa Minor.
As a celestial pole star, Polaris remains almost motionless in the sky while the other stars appear to rotate around it. This makes it a crucial navigational star, especially for travelers in the northern hemisphere. Mariners, explorers, and travelers have depended on Polaris for centuries to determine their direction.
Why Does Polaris Appear White?
To the unaided human eye gazing upward on a clear night, the North Star generally appears as a moderately bright white pinpoint of light. There are a few reasons why it looks white despite technically being a yellow star:
- It is quite far from Earth, so it appears dimmer
- The scattering of its light through Earth’s atmosphere shifts its color towards blue/white
- Yellow is difficult to discern for faint stars
- Pinpoint stars lack the resolution to see color shades
With a small telescope or binoculars, the hints of yellow become more apparent. But to the naked eye, it usually resembles a white dot similar to other moderately bright stars.
The Temperature and Spectrum of Polaris
The primary star in the Polaris system is a yellow supergiant belonging to the spectral class F7 Ib. This indicates:
- F-type: a medium-temperature star with surface temperature around 6,000 Kelvin
- Luminosity class Ib: a supergiant star
Its surface temperature gives Polaris the yellowish-white glow typical of F-class stars. However, it is still hotter and whiter than the Sun, which is a G-type yellow dwarf with a temperature around 5,800 K.
Polaris’ emissions peak in the green-yellow part of the spectrum
When examining the electromagnetic spectrum emitted by Polaris, its light peaks in the green and yellow wavelengths:
| Wavelength | Color | Intensity |
|---|---|---|
| 400 nm | Violet | Low |
| 500 nm | Green | High |
| 600 nm | Yellow | Very high |
| 700 nm | Red | Moderate |
This yellow-green peak matches the star’s 6,000 K surface temperature. However, the violet and blue wavelengths are scattered more strongly by Earth’s atmosphere, shifting Polaris’ appearance towards white.
Apparent Color Changes Based on Viewing Conditions
Under pristine viewing conditions, the North Star’s yellowish tint is more readily apparent. But the perceived color can change based on viewing conditions including:
- Light pollution – washes out colors so stars appear white
- Atmospheric conditions – smoke, haze, moisture scatters blue/violet light
- Telescope aperture – small scopes cannot resolve color well
- Eyepiece filters – filters like deep yellow make it appear more golden
With obstruction from atmospheric conditions or manmade light pollution, the subtle yellow hue is difficult for our eyes to pick up. The star’s light enters our eyes as nearly white.
To discern the North Star’s color, it’s best viewed on clear, dry nights far from city lights. Using telescopes with larger apertures also improves color resolution.
Changes Over Time
Over extremely long timescales, Polaris will change color as it evolves. But in our lifetimes, the yellow supergiant will appear white with just a hint of yellow:
- Now: white with a tinge of yellow due to its 6,000K temperature
- Near future: minimal change, perhaps a bit more yellow as it cools
- Billions of years: will transition red as it becomes a red supergiant
As the aging star exhausts its core hydrogen fuel supply, it will swell into a red supergiant millions of times larger than the Sun. Eventually the supergiant will shed its outer layers and explode as a magnificent supernova, leaving behind an extremely dense neutron star.
Conclusion
To summarize, the North Star Polaris has a surface temperature of about 6,000 Kelvin, giving it a yellow-white glow. But the star appears a plain white point of light to unaided eyes viewing it from Earth. Using optics reveals its subtle yellow color. Over long time periods the star will change hue, but for the foreseeable future it will continue shining its steady, white light down from the northern sky.
