How Do Astronomers Measure Distance?

Since astronomers can't actually travel to a star, they rely on two ingenious methods to measure a star's distance from earth. Watch BrainStuff break down the science of space measurement in this episode.

Whether the topic is popcorn or particle physics, you can count on the HowStuffWorks team to explore - and explain - the everyday science in the world around us on BrainStuff.

[ashleypatricia]

When I see you two on the pic showing who's hosting, I KNOW it's gonna be entertaining. Love you guys

[Ariminua]

People invent new units to make it EASIER to do maths. Instead of saying 1000 meters, it's easier to just say 1 Kilometer. Similarly, instead of saying 3.26 light years, we have the handy parsec to make it easier and not use so many figures. For novices, yes all these random values that have to be memorized may seem a bit much, but believe me, for others who use this on a regular basis, it's extremely helpful.

[axypolyas]

Hi! 
I'm not sure, i might have missed something....
How do they know the original brightness of a distant star?
Wouldn't that be required?
Is there a "general" brightness that applies to all stars so loss of that brightness can be then used to calculate distance?

[AslanAtreyu]

Thank you for explaining the Kessel Run!

[TopSchotter]

I think since astronomers use light to estimate distance they don't factor in relativity because the light is traveling at light speed regardless of the dips and bends in the space-time fabric so the estimated distance the light travels is probably not affected. However, the light most likely is not traveling to earth on a straight line so they probably keep that in mind.

[SLAPYHAD]

Thank you for this video. You guys earned a sub!

[IMRANULHAQUE-uxbg]

The best thing that there is no way to challenge these measuring techniques

[neomp]

yes, but how do they measure distance factoring in relativity? if spacetime is shaped by mass, and a gravitational field is a contraction of space, doesn't that mean that distance is changed by mass? and furthermore, isn't the apparent size of objects altered by that contraction of space?

[powelldiesel]

I knew the second method. However, the 1st method was a surprise to me. Both seem like pure speculation that is taught as truth in the schools.

[AtlasCho]

"SOH, CAH, TOA" stuff in Mathematical, . I like it!~

[TheDrunkenKhajiit]

Can we have a geometric rendering of the Milkyway ?

Thank you.

[corybuck]

In response to the first technique:
1) They *calculate* the distance using *measured* angles. They do not measure the distance. Otherwise they would have to travel the distance.
2) The sun is moving over 7x the speed of the earth due to its orbiting of the galaxy. I do not see that taken into account.
3) We do not know the speed at which the star is traveling. I do not see how we could even think to take that into account without first knowing its distance and direction of movement.
4) The use of parallax to determine distance requires that only the view point changes, while the target remains stationary. When I see the parallax of my thumb caused by switching which of my eyes is open it is the distance between my eyes that allows me to view the parallax of my thumb. However, neither my head or my thumb is moving while I am switching which eye is open, otherwise they would alter the results.
**note: this is assuming a spherical, heliocentric model as our indoctrination has taught.

In response to the second technique:
1) This is the brightness equation for stars: B = L/4πd2, where B = Brightness of the star in w/m^2, L = Luminosity of the star in watts, and d = distance to the star in meters. According to this equation, it is not apparently obvious to me how one would calculate (again not measure) distance without knowing the actual luminosity of the star in addition to its brightness which is known from measured RGB.
2) This method requires that there be nothing between the observer and the star, otherwise it would obfuscate the result. However, there are plenty of NASA articles about alleged water and other materials in space.
3) The technique is further complicated when you add in that it, the technique, was derived from the closer stars using the first method mentioned.

"We can invent as many theories we like, and any one of them can be made to fit the facts. But that theory is always preferred which makes the fewest number of assumptions. " - Einstein

We can dream in fantasy, but we must wake to the truth.

[atheistpariah]

You explained the parallax method well enough to where I can understand that some basic trigonometry would yield the answer. What is the distance formula for the color/brightness method?

[azraelblame]

Ok so all i got from this explanation is assumption after assumption after assumption. the first explanation assumes the distance to the sun is known, but how? how was it calculated in the first place never mind stars ASSUMED to be 400 light years away. how do you know they are that far in the first place? Redshift is also an assumption propagated as FACT. I mean if a star is 400 years (light years) away would it not mean that whatever changes it goes through takes 400 years to be seen from earth? so how would we know the brightness it has now is not its actual brightness unless we been observing it for 400 years? i cant even start with parsec and any other measurement becoz all of them just assume we know at what angle anything is, assumes we know the ends of the universe and generally assumes we been out there to verify. its fun stuff though just boggling with those numbers but i think at the end of it all they are just that, numbers.

[mrchichmagnett]

I always wondered this. There's a place called the whispering gallery and if you stand in a certain point in a room you could whisper something to someone all the way across the room.

[jpwiegand]

Bowlin and Strickand make a great team. They have a fun banter that really makes the science explanations easier to grasp.

[JacktheSmack]

When light is affected by gravity, since the light is beamed in all directions, any light effected during it's travel will produce a lensing effect which will be clearly visible.

[phalredenferd]

How do we know different angles yield the distance and why would that be accurate? How do we know the earths diameter orbit around the sun?

[ChristopherEverett]

Here is a question. How do they determine the chemical composition of an object at a distance?

Could you should us examples. Directly from NASA (if you will)? AND What technology exist or being worked on that does this?

[henrymark]

How do astronomers measure radius or diameter of planet or star in galaxy?? I am not interested in distance count.. Radius or diameter only