Stellar distance using parallax | Cosmology & Astronomy | Khan Academy

[@particleonazock2246]

You never fail to excel when teaching.

[@sethumadhavanparapurathu8598]

True

[@jasonzarnke8572]

Thank you for the excellent explanation though I do have one problem with this theory. Perhaps you can help clear it up. From what I have researched, the distance from the earth to the sun is 149,597,870,700 meters (92,955,807 miles). Converted to light years, that is 0.00001581 Now from what I have read, the nearest star it 4.37 light years away. If the distance from the earth to the sun was set at one unit, the distance to the nearest star would be 276,408 units away. To get a perspective of that angle, a toothpick is about 2.5” long and if that was the distance from the sun to the earth, we would be calculating a parallax based on the toothpick as one side of the triangle and the other side being 10.9 miles away. Or another way to look at it is the distance from New York to Los Angeles is 2451 miles. It that was the one side of the triangle, the other side would be 46.75 ft. Any triangle like that, for all reasonable purposes, is a straight line. I don’t see how you could actually measure those angles. And then the fact that the earth is rotating at roughly 1000 miles per hour and on an axis, how do you shoot “straight up” in such a way that we know is parallel to the line we shot “straight up” exactly 6 months ago on the other side of the sun. If our base lines are not parallel, the angle will be off. So, to get this measurement, me and a guy across the street, (93.5 ft away) would have to shoot two perfectly parallel lines from New York while walking slowly and gently rotating, so that a pin head in Los Angles is exactly in the middle of those two lines. And if we can get those correct, we could try and measure the angle and get an accurate distance. All of these factors combined makes me wonder how it is even possible to get any accuracy at all. Is there something I’m missing?

[@sexysexminecraft]

Technology is incredibly advanced.

[@tflip]

that's not an answer.. do some research.. the tech is not even available let alone on the so called Kepler scope to actually measure these angle at these grate distances.. they make the data up.. smaller local observatories will tell a much different story to the main stream "nasa" recordings regarding parallax motion.. (or lack of) shout out to Jason Zarnk tho.. great question once I understood the explination, lol... although just the words "tilt" and "axes" and "positioning" put major dout into parallax measuring and this is all based on us having being given the correct information regardind our own sun's distance.. one last thing, how fast is the universe apparently expanding?? lol does this not effect the rusult

[@jimkeller3868]

The The Sun isn't that far....millions not billons

[@iivXLGaming]

Of course you can, this is an educational video.

[@Kanbei11]

I think taking the route via the definition of the parsec would be more intuitive. Plus this is the perfect topic to touch upon the small angle approximation assuming the viewer understands radians

[@tristangutierrezmolina]

Is this video in Spanish version?? In KhanAcademyEspañol is this video (in English)... Thanks so much

[@TheBagleboy]

@JayDee98765 I may be completely wrong here but wouldn't the 2d plain just rotates on an axis to put the target star in the same 2d plain as our sun and the earth

[@JayDee98765]

@TheBagleboy The rotation would be moving through the third dimension? Its like trying to pin point a location in front of you 'down the street', unless its perfectly 'in front' of you, you have to take into consideration the third dimension... :(

[@werdnativ]

What is the maximum distance to which we can effectively use parallax for measuring distance? Is there any other method for measurement beyond that?

[@KitCat898]

Okay, question: If the apparent magnitude is equal to the absolute magnitude, what would be the distance of the hypothetical star? (Thanks for any help, I have a huge exam tomorrow and would appreciate input, as my astronomy professor is not the best in the world..)

[@shahineali5858]

So if we apply this to the moon, what distance would we get? Keep in mind, for 3/4 days every month the moon is above the horizon for 9 hours or less ( at 51 degrees N. Latitude). The rise/set sightings would be tangents to the circumference at the point of observation. There's a chance to win €500 (or equivalent in local currency) if you give the correct distance. Hint; it's under 4000 miles. See www.crystalcodex.com/competition.

[@GerardoZuniga]

How did you come up with the Total change in angle??

[@chissstardestroyer]

But, Mr. Khan, regarding how far a star is from the Earth, don't you need every single detail if you're planning an astronomical expedition, plus a lot of extra gear and supplies, considering survival odds?

[@JayDee98765]

@boeing747200lr :) I fully understand that part...its just, okay, so you have a 2d measurement using Pythagoras towards another point in the same 2d dimensions, but, if the actual location of the point is slightly to the left or right (the third dimension) of that point in the 2d dimension, then don't we have another isosceles triangle to calculate with respect ot he left or right direction? this is where i'm having a problem...

[@Voshronogi]

How is it you would measure the amount of arc seconds?

[@TheBagleboy]

@JayDee98765 yeah I am saying that the plane would be rotating through the third dimension. Imaging a situation in the video, except the star in question is in a plane 20` different to ours. could we not just change our view by 20` to move the star into the same two dimensional plane (for that it may require moving location by 20` N or S I'm not sure)

[@JayDee98765]

@khanacademy but... doesn't this method only work when the star we care about is in the same 2d plane as our sun and earth? Either i'm seriously missing something lol or we have to take into consideration the third dimension? the possibility that the star we care about isnt in the same dimensions as the isosceles triangles drawn? help :(

[@princemady9]

I have a question.Why can't we directly find the distance of the object(star) from earth,by using cosine i.e, adj/hyp as the adj would be 1AU and the hyp would be the required distance from Earth to the star..?

[@Theblazingchars]

Prince Mady because earths position is constantly changing as earth orbits around the sun and hence that distance also changes

[@BlueAsYourEyes]

How do you get the difference in angle? (the arc seconds thing) I don't get it.. What is the 'whole' angle?

[@drakedorosh9332]

Is there somewhere to look up an actual star? Public satellite database?

[@JayDee98765]

@TheBagleboy I see what youre saying, but even with the rotation of 20', you still dont have the true distance from you to the star? Try it with a piece of paper, put two points on each end, and rotate the paper, at least, this is what has dumb founded me. Perhaps Salman wasn't talking about 3d planes, it seems the only explanation, sir.

[@MercifulAreWe]

Hey Khanacademy, I've watched loads of your videos, and I love them all. I am so interested in astronomy, and cosmology. I was wondering though, could I use the information in this video for a demostrative speech in class? I would use the information and condense it, I will not use the video, but perhaps if i copied some pictures? Thanks for whichever decision.

[@chissstardestroyer]

Wouldn't the Parallax be almost nonexistent for a star in the sky, Mr. Khan, for aside from the Sun/Sol/Helios, none are closer than 4.2 light-years, so with the naked eye that would amount to no change at all. But planets would change via parallax, as they are much closer, wouldn't they, Mr. Khan.

[@timothyrenaud7348]

How do you measure the parallax angle ?

[@78anurag]

The parallax angle+ Angle between star and earth=90° The parallax angle= (90-Angle between star and earth)° The angle between star and earth can be calculated easily by a telescope with an inbuilt protractor

[@TheBagleboy]

@JayDee98765 ahh yes I see now. Thanks for pointing it out to me

[@mossaic13]

am I missing something? every youtube channel teaches this... But are all stars 90* above the sun? and How does one go out and take star angle A measurement in summer, B in winter. It would have to be at night right? looking away from the sun right? or am I just confused?

[@Horinius]

The cardinal points are wrong for sky view! They should be either N E W S or S W E N

[@ThatTechyStoat]

How did you find 1.5374 arc secs?

[@AdaManfaat]

This is my question too😭. Anyone can help?

[@xRoRox]

@@AdaManfaat same here, I’ve googled high and low yet can’t find any answers

[@kaloomuwana9077]

On every single video ive seen they always draw the two angles as being the same, is this always the case? Surely the two angles will be different in certain cases?

[@stevelarry154]

as I understand it, for any star at any angle, we can find 2 periods in a year when earth is forming equal angles with the stars and the sun. Think about that in 3d

[@BlueAsYourEyes]

You didnt explain how you would measure the total change in angle/ whole angle in arc seconds please explain and what the difference is between total change in angle and whole angle? Your video is just confusing me

[@mrinalsood9887]

How do the sun, earth and the star are lying in the same straight line in your diagram?

[@78anurag]

They don't have to, he just took this diagram to make stuff easier

[@BlueAsYourEyes]

You do know you dont have to do 90-theta right? You can just use theta as its the same angle as the one coming from the star between the earth and sun..

[@Horinius]

KZbin chooped out my "new lines"... I wanted to write N (1st line) E W (2nd second) S (3rd line) and similarly for the other one

[@BlueAsYourEyes]

I just dont understand why you cant measure the total change in angle in degrees instead of having to convert it back

[@Dekulink333]

You don't. You measure the total amount the star has moved and divide it by two.

[@av733]

Ha ha, I see you have got rid of the crappy windows calculator.

[@BlueAsYourEyes]

Your videos are usually really easy to understand but this one goes too fast towards the end and you don't really explain very well

[@jimkeller3868]

A good math lesson, but stellar parallax is NEVER determined in this way. Don't teach the technique if you don't know.

[@MannyManny-pf8sb]

nut

[@charliefoulkes8363]

Although this was very helpful and informative, i think you mumble on to much and repeat things three or four times, it gets quite irritating and boring to listen to after about 5 minutes. if you didnt repeat your words or mumble things that you didnt need to i think you could cut your video time down to 8 minutes

[@Horinius]

KZbin removed the "new line" characters from my previous comment. Sorry, but can't help.