This is mind blowing to me. I always thought that we see colors with our eyes and thats how our brain works.

But if you visualize something in your head, like a fully detailed apple, you can see and change the color of the object in your imagination.

How does the brain store color information?

Do they return to normal levels relatively quickly or can they persist for a time?

Are galaxies spherical or flat?

For example, (I understand that up and down don't really matter, so bear with me) if we look at a picture of the Milky Way Galaxy on a plane... If you want to move from one arm of the galaxy to the next, could you just move UP and out of the current arm and then over and DOWN to a different arm?

Secondary question for if the first one is correct, if you are able to move "up" and out of the arm, where are you? Is that interstellar space too?

I thought about the tumor issue because, for example, elephants are bigger than humans and therefore have more proliferating cells and therefore more likely to undergo a mutation, I don't know if my reasoning works

I am aware of hypotheses that suggest that Venus underwent some kind of global resurfacing event that would have wiped away evidence of older craters. However, I cannot seem to find a description of what this would have actually looked like? Was it just a whole bunch of volcanoes all going off at once? Did parts of the crust literally break off and sink into the mantle? Or is it something else I'm not thinking of?

My 14 year old niece and I were discussing this topic and we both came to different conclusions, but we’re really curious as to what would happen here. I hope my question makes sense. In summary, would the astronauts go flying apart or would they stay in the same spot? Excited to know the answer from some experts!

I seem to have a basic grasp of pulsed wave Doppler imaging: small packets of ultrasound energy are transmitted than there is time for the returning echo - the length determines the PRF, usually in the kHz frequency.

I don't seem to understand though how exactly sampling of the returning echo happens. Let's say I transmit a 1 Mhz frequency US burst and the Doppler shifted returning echo is 1,1 MHz so I have a shift frequency of 100 Khz. Isn't the transducer just able to detect the returning 1,1 MHz echo and calculate a velocity from the shift frequency? Why do I have to sample the returning 1,1 MHz signal with a PRF of at least 200 kHz?

I get the idea that you need to sample a sinusoid wave at least two times per cycle to accurately depict it but I don't get why the shift frequency is determinant here and not the frequency of the returning echo itself. Aren't we sampling the returning echo frequency and then calculating the shift frequency from that value?

Is it a very basic principle that I'm overlooking?

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