Also, why do some faint stars seem to disappear when we look directly at them, but can be noticed when we look at a nearby patch of sky?
krystar78: planets twinkle too. twinkle is caused by the Earth’s atmosphere being inconsistent density which causes varying refraction angles. sometimes strong sometimes not. any light that goes thru the atmosphere twinkles.
if you were on the ISS and look at the stars, they don’t twinkle.
MayIServeYouWell: Starlight is from so far away, it’s essentially a single point of light with near zero diameter. When the atmosphere refracts that light, you can notice it more, because the amount of refraction is greater than the diameter of the source.
Light from planets is refracted too, but since they’re a lot closer the source isn’t zero diameter, it’s just slightly bigger. The refraction is more obscured by the diameter of the light source.
So, planet light is dimmer light, but coming from a larger diameter source.
LausanneAndy: Stars = 1 pixel
Planets = 2 pixels
Earth’s atmosphere continuously warps the light enough for 1 pixel to momentarily disappear. But usually not enough for 2 pixels.
ObiWanKenobody: The answer to the second half of your question has to do with the two different types of light detecting cells in our eyes. They are called “rods” and “cones”.
Rods are good at detecting dim objects (stars in this case) while cones are good at detecting bright objects. It just so happens that the center area of our vision is mostly handled by the cones, while our peripheral vision is handled more by the rods.
So when you look a little off to the side, you’re forcing your eye to use the more light-sensitive rods. This technique is called “Averted vision.” Most people need to look 5-20 degrees to one side or the other for the best effect.
studentofcode: Fun fact: when I attend star parties we often pan with our scope and usually find deeper/fainter space objects using our peripheral vision. You know you got something when you see it from the corner of your eye.
skinsinc: The center of our vision is less light sensitive than the sides, so if you look directly at something, you see it with less sensitivity, or it seems darker, if you look at it out of the side of your eye it becomes brighter. For things just on the line between bright enough to see and not (stars and meteors and things), sometimes they disappear when you look directly at them.
bobthorns08: Stars twinkle because they’re distance is so far away from the Earth that when its light passes through the atmosphere, it is bent countless times due to refraction, making it look like as if they were twinkling. Planets on the other hand do not twinkle. They are relatively closer to the Earth than those distant stars, so planets may seem larger in comparison. Due to its closeness, the light coming from these celestial bodies does not bend much due to Earth’s atmosphere.
BAC_Sun: Part of the problem with planets/stars disappearing when you look directly at them is the fact your using the cones in you eyes which are more sensitive to color, but the rods (which make up more of your peripheral vision) are more sensitive to just seeing light. They also don’t get fatigued as easily as cones.
LithiumEnergy: Imagine you’re looking down on two lights at the bottom of a pool. One is a tiny little LED and the other is a big fat glowing orb. Disturb the surface a **tiny** bit and the LED will seem to move around dramatically, but the big fat orb will seem to stay relatively still.
chandler11able: Finally. Something I can answer. Thank fuck. Stars are millions of miles away from the Earth. This means it requires the light admitted by the stars to travel very long distances which causes the light to be distorted . With planets, the light is reflected off the soon to earth, a lot less distance is traveled allowing the light to reach the Earth undistorted.
reggit99: I always assumed it was because the image of the start got burned into your eyes like when you look at a lightbulb, because I can always see dim stars at first but after a few minutes of looking at brighter stars I can’t see dim ones anymore when looking right at them.
stabcuntmcdickerson: Cone cells see color. They are less sensitive to light so work better in bright light. Rod cells see black and white. They are more sensitive to light so work better in dim light.
Cone cells are more dense toward the center of your retina. Rod cells are more dense toward the perimeter. So when you look directly at a star, you are using more cones and the star seems to disappear bc the cones can’t pick it up.
Try walking in the dark but only using your peripheral vision. You’ll find that you can see a lot better than by looking directly at things.
levlup1: For the stars there is a shift in light. You first see the blue light coming from the star then you see the red light shortly after.
JiN88reddit: “Twinke” is in fact not related to what star/planets it is, but more to the interference of light from where you perceive them (earth atmosphere of different and changing density compared to the vacuum, etc..). Most of the time you will see stars “Twinkle” more due to them producing light; planets don’t produce light but rather reflect lights.
b-doggiedog: Ok so I haven’t actually seen this explanation yet and some people this might seem wrong but it’s not:
A lot of stars we see aren’t actually just one star but 2 orbiting each other. The twinkle comes from (not from our atmosphere) but from (and I can’t remember the exact term from astronomy) basically orbiting each other. Some stars have rather large planets orbiting them which can also cause this effect.
So yeah. Downvote away but this is what was explained to me by someone who has studied in the field of astronomy a long time (PhD).