Cosmic Distance Ladder: Parallax 1
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- Опубліковано 25 сер 2024
- Introduces the concept of parallax and how our eyes see depth perception. We then explain how this can be applied to astronomy to measure the distances to nearby stars. The first step in the cosmic distance ladder.
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The background stars can be used as reference points to measure the apparent changes in the nearby stars positions, which is easier than trying to find some other absolute reference frame. Think about if you were to take two pictures of a patch of sky at different times, if there were only one star, it could have moved or the camera could have not been aimed exactly right. By overlaying the two pictures and matching up the background stars (unmoving), we get rid of the camera aiming errors.
Absolutely; it wasn't until the mid 1800s that astronomers could even measure the parallax of a few of the very nearest stars. In fact in the 1500s and 1600s the unobserved parallax was considered to be scientific evidence against the Copernican model for the solar system. Parallax angles that small would require distances so great that many people considered implausible. It wasn't until the mid-1900s that we could measure the parallax of more than a few hundred stars.
Thank you for the detailed insight! :) The stars (galaxies) are full of mysteries, and that only adds to to my perspective.
Thank you. This really helped.
I think the Hipparcos satellite (that has given us most of our best parallax measurements) had more sophisticated ways of stabilizing the cameras and setting up an "extragalactic" reference frame for its measurements, but I'm not as sure about the details of this.
good explained
This was very well and intuitively explained. :) However, getting the measures by ourselves of the actual parallax angle of one particular star could be indeed challenging.
I think its impossible. there are no stars that we can see 90* to the sun. This parallax formula just sounds cool and complicated, designed to scare people from questioning. Not one youtuber astronomer channel, nor website, explains how to get that measurement for yourself.
Very clear explanation, :)
Right so 4:20 is the geometry part of this method.
thanks a lot!!! but i didnt quite understand that why star moves in a circle? it doesnt getting further or closer so it should move in a straight line? thanks again
It's not that the star is moving in a circle, but that our reference point (the Earth, which is in orbit around the Sun) is moving in a circle. You can simulate the same effect if you hold up your thumb at arms length and then move your head in a small vertical circle. It will appear as if your thumb is moving in a circle compared to whatever objects are behind it.
Thank you very very much sir!
thanks a ton
I know this may sound like an unintelligent question, but is it possible to use the parallax method without waiting a six-month time period? I am madly trying to finish my eighth grade science project that is due in less than a month.... I would choose a simpler project like "why my dog snores" but I found this very interesting. My science teacher hasn't been much help though so any extra advice that could help me would be great. :-D
Can you please explain a bit more about measuring the angle of parallax according to 8:35 ?
I probably could have explained that better in the video, but in practical terms we use the more distant background stars (that essentially don't show changes in their apparent positions) as reference points and measure the changes in the apparent positions of the more nearby stars. Essentially, if you took pictures of the same region of the sky over the course of a year, most of the stars you could see wouldn't show any relative movements, but the more nearby stars will trace out an oval on the sky. We can measure the angular size of the widest part of that oval and that corresponds with twice the parallax angle.
thank you very much! :)))
You made a mistake.
tanθ=Perpendicular/Base
So it would be d/1AU not 1AU/d.
+Md. Tunazzin-Ul-Arefin Instead of saying tan(theta) is perpendicular/Base (this is only true if theta is the angle beside the base side) use tan(theta)=opposite/adjacent. From the angle theta that I draw on the diagram, the opposite side is the 1AU length side and the adjacent side to the angle theta is the distance.
Looks to me like someone needs a much bigger telescope in say Pluto’s orbit, to better measure those background stars.
ok... but you know what? how many stars are 90* to the sun? the only stars we can see are away from sun, the night side. Every youtube astronomer channel all, give that same example. Am I missing something, or is this formula complete bullshit?
Four years later, but in case someone else has the same question. As an analogy, stare directly ahead of you, pretending that each eye is earth, half a year apart (the baseline). Can you only see things 90 degrees ahead of you? Of course not. You can look around. You can look left, right, up, down... what would that resemble in astronomical parallax? Taking the two images at different times of the year, perhaps also at different times of the day in different areas of the earth. You could point the camera directly away from the north pole, for example, to get a much different view than on the equator. As long as you know the difference between your pictures, you can calculate your baseline. Right now, I think you're assuming that the picture can be taken only two days a year? In actuality, they just need to be taken half a year apart.... technically, you could take the two pictures the same night as the earth is ALWAYS rotating the earth, but your baseline would be miniscule. Even now, the 2AU baseline is really, really small in the cosmic sense, but it's the best we can do. Taking the photo twice from Neptune in the Neptunian year would be better, as an example!