
How Do We Measure the Distance to a Star? - yaseen-rob
https://www.scientificamerican.com/video/how-do-we-measure-the-distance-to-stars/
======
xenophonf
Parallax is barely the first rung of the cosmic distance ladder:

[https://en.wikipedia.org/wiki/Cosmic_distance_ladder](https://en.wikipedia.org/wiki/Cosmic_distance_ladder)

------
shove
It's a huge pet peeve of mine when the science part of this kind of
edutainment media is either wrong, or (as in this case) dumbed down to the
point of uselessness. The triangle diagram here is completely wrong, and yeah,
it uses high-school trig, but c'mon--if it's something we all supposedly
learned in high-school and your audience is high-school educated... Show the
actual diagram and the actual math!

~~~
selimthegrim
Scientific American isn’t aimed at professional scientists or STEM majors.
Think bright middle class high school kids.

~~~
jhayward
Back in the 1960's my grandfather, who didn't have a high school education
(farm raised, 1903-1994) had a subscription to Scientific American and would
read them cover to cover.

Starting when I was 7 or 8 he would talk about the articles with me while we
were working on things, either in his shop or cutting timber or repairing
things around the farm. He would ask probing questions about the subjects,
look for implications, make connections to other things he knew, all the kinds
of things you want a scientific mind to do. Despite a lack of formal education
and wearing a pair of blue jean overalls and muddy wellington boots, with
tools in his hands, he was a smart and erudite for his circumstances.

He gave me his entire library when I was in my early teens. The first program
I ever wrote, Conway's Life, was taken after a Martin Gardner article I read
there. I credit those talks with my grandfather, and the articles I read, with
a large portion of my being drawn to STEM and seeing it as "something for me".

SciAm was once a great institution trying to spread knowledge of the explosion
of scientific understanding that was happening at the time. I miss those days.

~~~
selimthegrim
I used to read the Connections column by James Burke regularly but he quit
writing it shortly after my family actually sprung for a subscription :(

------
msisk6
Surprised it wasn't mentioned in the video, but this is where the term
'parsec' come from. A parallax angle of 1 arc second means the object is 1
parsec away (3.26 light years).

------
chrisBob
They have some beautiful animations, but can any astronomers confirm if people
actually do it this way?

From class I remember that you can also determine the distance by measuring
the coherence of the light coming from the star at two distant points on the
order of 100m. In theory this would require more equipment, but has the
obvious advantage of taking less than 6 months to get the results.

~~~
eesmith
[https://en.wikipedia.org/wiki/Cosmic_distance_ladder](https://en.wikipedia.org/wiki/Cosmic_distance_ladder)
\- "At the base of the ladder are fundamental distance measurements, in which
distances are determined directly, with no physical assumptions about the
nature of the object in question. ... The most important fundamental distance
measurements come from trigonometric parallax."

~~~
xtacy
Also highly recommend Terry Tao's talk on the cosmic distance ladder:

[https://terrytao.wordpress.com/2010/10/10/the-cosmic-
distanc...](https://terrytao.wordpress.com/2010/10/10/the-cosmic-distance-
ladder-ver-4-1/)

------
crazydoggers
Parallax is not the only way. Cepheid variables are also used, I think more so
than parallax, since parallax is only accurate for somewhat nearby stars.

[https://en.m.wikipedia.org/wiki/Cepheid_variable](https://en.m.wikipedia.org/wiki/Cepheid_variable)

~~~
antognini
Yes, but Cepheids are calibrated, fundamentally, by parallax. (I believe that
no Cepheids were actually close enough to be calibrated directly by parallax,
at least until Gaia, so they had to be calibrated by other techniques which
were, in turn, calibrated by parallax.)

------
dyukqu
Here is a 9 videos playlist (that I find helpful) about the methods
astronomers use to measure the cosmic distances:
[https://www.youtube.com/playlist?list=PLEE8A6CB118FADED4](https://www.youtube.com/playlist?list=PLEE8A6CB118FADED4)

------
selimthegrim
The author was my undergrad classmate. She did biology or biological
engineering IIRC, glad to see she’s hitting the big time.

------
js2
[https://en.wikipedia.org/wiki/Stellar_parallax](https://en.wikipedia.org/wiki/Stellar_parallax)

------
amelius
How accurate is parallax, given that stars bend light?

~~~
throwawaymath
It's accurate to within 100 light years. See
[https://starchild.gsfc.nasa.gov/docs/StarChild/questions/par...](https://starchild.gsfc.nasa.gov/docs/StarChild/questions/parallax.html).

~~~
teraflop
"Accurate _to_ within 100 light years" isn't really a meaningful statement.
The page you linked to is a simplified explanation that says the method is
only accurate enough to be used _for stars within_ 100 light-years of Earth,
which is approximately true. We have measurements of more distant stars, but
they become increasingly inaccurate with distance.

To be more precise, the relative error of a parallax distance measurement is
proportional to both the measurement error and the distance. For example, the
Hipparcos mission measured parallax with an accuract of roughly 0.001 arc-
seconds. That corresponds to a 0.1% error at a distance of 1pc (~3 ly), or 1%
error at a distance of 10pc, or 10% error at a distance of 100pc, and so on.

Note also that the page you linked was written sometime around 2002; since
then, more sensitive measurements have been done, e.g.
[https://arxiv.org/abs/1401.0484v1](https://arxiv.org/abs/1401.0484v1)

------
chmaynard
Understanding this is not a high priority for me. Just sayin'. :)

~~~
contravariant
Glad you could still find the time to tell us.

------
zunzun
The simplest method would be to send a spaceship there and back and calculate
distance based on fuel usage.

