Stars are an immense wonder, but they have so many fascinating properties that leave us with many questions and sometimes feel left clueless. Everyone loves to stargaze every now and then, and some of you may have seen them change color from time to time.
So, why do stars twinkle red and blue? Stars twinkle red and blue due to refraction. This is when the star’s light enters the Earth’s atmosphere, and it spreads in various directions due to multiple winds, temperature changes, and atmospheric changes such as differences in density. Astronomically, this is known as scintillation.
There’s a lot going on here.
And it all results in quite frankly, breathtaking views for us here on Earth.
If you keep reading, you’ll also find out why stars can twinkle in different colors, and why some stars do not appear to!
Why Is There A Star Flashing Blue And Red?
A star flashing blue and red is going through a refraction process known as scintillation. Alongside density, temperature, and other atmospheric changes, these factors cause the light entering Earth’s atmosphere to change paths, which usually end up in different colors, primarily red and blue.
When the wind in the atmosphere is moving inwards and outwards, the light traveling from the star is refracted, causing a chromatic aberration that makes the stars look like they’re twinkling different colors.
Additionally, if temperatures or wind changes are more extreme, the color changes could be more visible than on evenings with calmer atmospheric conditions.
Not all stars twinkle the same colors or at the same brightness, and one of the main reasons for this is the angle at which you’re viewing the twinkling star.
It’s also possible for a star to twinkle multiple colors, indicating several atmospheric elements here on Earth and around the star are working together.
If a star displays a blend of red and blue, it could be at a sweet spot in its life cycle where the star’s temperature is cooling.
Or the atmospheric conditions of temperature, dispersion of light, and air density may be just right to display the colors in such a way.
If you’re looking at a star that’s directly above you, the light has a straighter path to your sight, which means there will be less refraction and less of a flicker from that star.
Now, if the star is further near the horizon, the light has to travel through much more of the atmosphere, causing more refraction, making the star look like it’s twinkling more.
The brightness of the star can also have an effect on the bright colors we see on Earth.
For example, Capella, the brightest star in the Auriga constellation, was easily seen flashing red and green in Oct. 2020.
This was because it was at a low horizon, causing us to view it through more of the atmosphere and that it’s the brightest star in its constellation.
These elements led to a flicker of bright red and green.
What Causes Stars To Twinkle Different Colors?
This is due to multiple factors; scintillation causes chromatic aberration, which is the inability of a lens (our eyes) to focus all colors to the same focal point. Dispersion is what makes this occur, which is when the wavelengths of light alternate with the refractive index of the lens. When stars display different colors, this is due to the star’s temperature and if the star has any other elements in its atmosphere.
Cooler stars tend to display a red color, while hotter stars will scintillate a blue or white color.
Red stars are around 5,000 degrees Fahrenheit, the Earth’s Sun is approximately 10,000 degrees Fahrenheit, green stars are 18,000 degrees Fahrenheit, and the hottest stars, white and blue, are about 45,000 degrees Fahrenheit and above.
Other factors can include the distance of the star from the Earth and the age of the star.
When you look up in the night sky, you may see some really bright stars, and then some that look dim or have a weaker twinkle to them.
It could be because one star is further away; it could also be that its life cycle is coming to an end.
Once again, temperature changes within the star are a primary indicator of its bright color.
So, if the star is dying out, it’s getting cooler, and it has a red flicker that seems a bit dim.
Our own Sun has its yellow, orange color due to its average temperature being around 10,000 degrees Fahrenheit.
To recap on this section, it all comes down to the temperature and atmospheric elements of every star for each color.
The brightest stars will be the closest, youngest, and hottest stars, while the dimmest will be the farthest, oldest, and cooler stars.
While the dispersion of light changes is due to the star’s distance from Earth and chromatic aberration of the light through the atmosphere.
Why Do Some Stars Twinkle and Others Don’t
Interestingly enough, in most cases, it is usually due to a planet, satellite, or it’s another star’s location or distance.
You’re looking at the night sky, you see a handful of stars twinkling away, and you can’t help but wonder, “Why aren’t the others twinkling”?
Planets can be mistaken for stars all the time, considering they’re so much closer to Earth than the stars.
They shine as a disk rather than a pinpoint of light from really far away.
Although the light from the planets is also refracted through Earth’s atmosphere, it doesn’t travel the same.
Essentially, light paths from the edges of the planet tend to cancel each other out through the atmosphere, causing the light to appear more steady, rather than the erratic chromatic aberration from a stars pinpointed light.
It’s also important to remember that the Earth’s atmosphere is the key player that causes us to see flickering colors with varying brightness and intensity.
If we were to look at the same stars and planets from outer space, they would all have an equal and stable shine.
Another note to reference is that some stars don’t seem to twinkle, which could simply be because of their position.
If you took a star that’s directly above you and moved closer to the horizon of your view, it would certainly look like it’s twinkling much more.
Once again, the light of the stars is traveling through more of the atmosphere, causing more chromatic aberration of light.
You can also tell the difference between stars and planets by the steadiness of light in contrast to the twinkling effects starlight has through Earth’s atmosphere.
Another perspective would be your own location on Earth.
If you see a super bright twinkling star at Point A and then move to Point B, far enough where the star’s location has moved from your viewpoint, it could change the twinkling frequency, how visible it is, and even the brightness of color.
What Are Some Main Characteristics of Star Colors
Star colors can be correlated to a few main factors like the temperature and mass of the star, whether it be a Dwarf or a Supergiant.
When it comes to red stars, the cooler of the ranks, it’s common to find some titanium oxide molecular bands, while in orange and yellow, you’ll discover absorption lines of neutral metallic atoms.
Once you get up to the hottest stars, or white and blue, you’ll find much more extreme characteristics like a powerful UV continuum, helium lines in absorption or, ionized helium lines in emission or absorption.
This is all depending on multiple factors like luminosity, mass, and surface temperatures of each star.
Additionally, there are different types of stars.
For example, our Sun is a Dwarf star and one of the smallest there is. When it comes to the largest, the Super Giant takes the cake.
Betelgeuse is the second brightest star in the Orion constellation and one of the brightest in the night sky while making it relatively easy to see.
Although our Sun is hotter than this star, Betelgeuse is around 1,000 times larger.
Factors like these could also affect how bright a star is compared to another, not only by temperature, age, and atmospheric factors but by the type of star.
It should also be noted that the blue spectrum within stars has a wide range in luminosity.
Blue stars can range from a luminosity of 80-1,400,000, while the red to white color spectrum only goes from a luminosity of 0.4-6.
Those numbers alone can help explain why one star is brighter than the other and can help you understand what type of star it is based on how bright it is in combination with its color.
It’s interesting how a variety of natural elements from our planet to outer space can create such a spectacular visual show in the night sky, and none of it would be visible if it weren’t for the Earth’s complex atmosphere.