Stellar parallax | Stars, black holes and galaxies | Cosmology & Astronomy | Khan Academy
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- Опубликовано: 27 авг 2024
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Another version of the stellar parallax introduction. Created by Sal Khan.
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@onecrazysim there are many ways to do it. I did it this way since I found it easier to visualize.
I'm just 13 years old but this is so easy that anyone can learn it
Great mathematic explanation. Exactly what I was looking for. 👌
The angle measurement is often measured relative to distant stars/galaxies, for example if you are looking at a "near" star you would measure its parallax angle relative to that of a "very far" star which you would approximate to have a zero parallax change as the Earth orbits due to the distance between Earth and the far star being much greater than that of Earth and the near star.
Useless fact: The astronomical distance "parsec" is the distance (x) at which the parallax is 1 arc-second.
Your videos are really cool and educational. As a visual learner I really learn a lot from the style of your vids. :)
What exact instruments are used to detect theta??
Did u find the answer athenntic Rhythmic??
This is basically how range finders work, correct? I know that you can calculate a distant object by looking at it from two points (knowing their distance apart) where one is to be the "right angle" of the triangle and the other is to be your measured angle 90 - theta where theta would be how far over you have to look from changing your position. Of course you are going to get more accuracy the further those two points are with respect to the distant object.
How do we know how far away the sun is? If our solar system is ripping through space at over 600,000 miles/hr and the other celestial bodies are also moving then the ranges would be changing.
Best question ever in history!
I think that Sal should represent the distance "d" as 1 AU to make the trig a bit easier.
At 7:22.
Hi. First, congratulations to khanacademy for all the videos in YT =).
I have problems with the audio... is very soft (at least, in this video). Thanks!
very nice video
very useful for GCSE revision
Jon Keevash Same with his other videos
@fosheimdet "theta" greek letter often used to name an angle (like alpha beta etc.)
them my question is: How do you know that the sun is directed 90 degrees at the star before hand?????? how can we possibly figure this out?
they figured out the angular distance (declination) of the Sun & the star from the earth.
does that answer your question?
anyone can correct me if im wrong
When the parallax is maximum is the time when the earth-sun distance and the sun-star distance are perpendicular.
العلم نور والله
How do you know when you should start measuring, how do you know when the star, the sun and your position on earth forms an exact 90° angle if you don't know the distance to the star?
You are not using the star to make the 90 degree angle. The suns position at sun rise gives you line between you and the sun that is perpendicular to a line from you straight up. These lines, being perpendicular, have a 90 degree angle between them. This is an approximation but there are ways to improve its accuracy based on more accurately measuring the angle between you and the sun and creating an exactly perpendicular line.
You then determine the angle of the star from straight up. You don't need distance for this. There are tools to help with this and measuring the difference between your created "up" line and the apparent position of the star. No matter the stars distance this angle will be the same.
Edit: correction, if you used sun set one day, 6 months later you would do it at sunset not sun rise. Misspoke there.
@DiabolicProductions2 agreed. was just having some fun.
For you are basically trying to triangulate your position based on landmarks, or the position of other things at that, Mr. Khan; that is how I guessed that it would be, but I want to know what you think. Surely the principle seems very similar to triangulation regarding Parallax.
It amazing what you can with ingenuity.
Sal..is it one of your plans to make videos on foreign languages?such as Spanish?
HOW DO U MEASURE theta
Do you really need both measurements of the same Theta angle? And then does it allways take six months to calculate the parallax for a star? Besides it sounds like you need to be very precise about the time you take your measurements to have that 90' with the Sun.
Wow, a very interesting video. I don't know how I ended up here, but I enjoyed it. ;D
0:48 "As you shit"
"As you shift.."
When he said 'to the west' at 5:36 did he mean to the east?
Nice video, I'm trying to this one out...if the galaxy is moving 1.3million mph, and our solar system is orbiting around the center of the MWG at 45k mph, how is it that we see the same star formations throughout history? don't these other stars move at all? maybe I'm just a dummy but it doesn't make sense to me.
David Parry first of all pat yourself on the back for making yourself feel smart. second, you didn't answer anything, you just assumed i'm a dumbfuck. you are telling me human beings haven't been seeing the same constellations for thousands of years?! I don't need someone to "tell me" k thx. if you have anything useful to add please do, such as, information, if not, keep useless banter to yourself.
see you didn't answer anything b/c you think this is some sort of smart contest. I genuinely want to know things so I really don't care if you are smarter or not. If these stars change position in even ONE year as you say then why after 3k years or whatever do the constellations still line up so closely? I realize space is big, but 1.3million mph for 3k years , plus all the secondary motion caused by gravity, it doesn't seem like we would have the same viewing or even close. can you say the change in position is due to expanding universe or due to revolution/rotation of our planet and the ones being viewed?
David Parry you see how it says David Parry?? that means it's a message posted at you, just like you are doing to me. you are also directly responding to what I type. so mr. crazy person who the fuck are you talking to if not me? ask me if I know how THIS technology works when you yourself don't know. kinda like how you cant explain anything in space you say subtend and now im suppose to know exactly what you know. you're pretty fucking stupid for a nerd.
You are right that the star itself moves as well. Which is why, when astronomers actually do these measurements in the real world, they not only take one initial measurement + a second one six months later. They additionally take a third measurement, six months after the second one. This way they obtain information on the star's angular displacement "on Earth's way back" to its initial position, so to say. They can then use the difference between (measurement 1 and measurement 2) and (measurement 2 and measurement 3) to subtract the star's own motion.
So if while going from position A (initial measurement) to B (six months later) we calculate a parallax angle of say 1 arcsecond, we would expect to obtain the exact same result when going from B to A (moving back to our initial position in orbit). The difference between the parallax angle when going from A to B and from B to A will be the result of the star's own movement.
In certain cases, such as with binary stars (which undergo significantly more movement than a typical star) we need to take even more than three measurements.
Let me know if this makes sense.
Smartest comment
@mignik01 um, no i don't actually. but honestly, i don't think anyone cares. lets not start an argument, let learn about Steller Parallax!
Very nice, unfortunately, it has been discovered that the Earth only moves a short distance 14036K a year. So in 6 months we would only move 7018K. as per the TYCHOS MODEL of the solar system. a new modle based on an additional movement just uncovered, or discovered, by Simon Shack. Thus bringing the stars 42366 TIMES CLOSER than your process.
You do an excellent job explaining it.
Mr. Khan, isn't Parallax basically the original inspiration for trigonometry, pray tell?
I would rather measure the angle between the sun and the star rather than theta. Wouldn't it be easier?
Why do the moon and stars move together with no stellar parallax? Why does the moon give a cooling light?
How do those "sensitive instruments" measure the parallax angle? can someone please answer
By measuring the change of the position of a star relative to further ones between the moment when we're at one side of the Sun and the moment when we're at the other one.
@khanacademy can you do a video on Dark matter?
If things further away do not seem to move against things closer to your position, someone explain how the moon travels across the sky at the same time as all the stars which are allegedly hundreds of light years further away. (see moon and star timelapse footage)
They’re both “not moving” at the same rate due to the earths rotation. We measure these things with both the earths solar orbit as well as its axial rotation.
why is this video almost exactly the same as the last one (in the playlist)
Tried to leave a comment. But at part about solar system. And I'm wondering what the heck has really take. Place over past 5ish years and I'm at a loss of words for what I'm suppose to do. Really it seems hopeless due to all negative and plans I had extracted for not my use .. so trying to figure out what's possible and plausible for me. But thx again for lecture and breather ✌️
@horaceholt @horaceholt
@pheonix81@pheonix81
Sorry for extra posting just trying a few things
1.416
you can always skip the first 4 minutes of the video if you watched the previous one
0:49 "As i shit..." lol. Yeah, sorry...
the only video so far that I got lost in.
@DiabolicProductions2 do u have a problem? I didnt ask you for anythin
I am so dumb, lost the plot after 30 seconds:(
e
niber
Is this a coding tutorial? LAWL
As I shit lololol
@mignik01 You want a fricken cookie? No one cares that you are first!
First
1 person wants to live in a cave.