Questions tagged [parallax]
36 questions
18
votes
7 answers
What is a simple argument to prove that the stars in the sky are farther away than the Moon from the Earth?
How do we know, without using modern equipment, that the stars are further away than the moon in the night sky? Further, is there a simple and actionable argument to prove that this is indeed the case? Additionally, I would like to know how people…
kbakshi314
- 2,430
16
votes
2 answers
How is the parallax angle actually measured?
I understand that parallax is used to measure distances to stars. But how is the parallax angle actually measured?
In the parallax diagram we have two similar triangles, but we don't know any values other than the distance from one side of the…
bgrantham
- 395
9
votes
2 answers
How do astronomers measure the parallax angle?
How do astronomers measure the angle p?
"Instead of closing one eye and then the other, we observe a star six months apart, so that we are on opposite sides of the sun for each observation. Watch the star shift against background star field, and…
user349993
8
votes
3 answers
Parallax, obliquity, precession, and Orion?
Today, the obliquity of the earth is about 23.4°.
6500 years ago, it was about 24.1°
Imagine the blue square is the constellation of Orion, and the yellow star is the sun. Viewpoint B is you, on earth, today, when the obliquity is 23.4°. When you…
Rob
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8
votes
1 answer
When and how were relative distances to the planets first measured?
I understand that the absolute distance to a planet can be measured using earth-baseline (e.g., diurnal) parallax, and that the first reasonably accurate such measurement was made for Mars by Cassini (and his assistant Richer) in 1672, and then,…
orome
- 5,209
6
votes
5 answers
Why don't the relative positions of stars and other objects in a galaxy change over the year?
Though the identifiable stars in a constellation (say Andromeda) and a galaxy (say the Andromeda galaxy) are situated light years apart, why doesn't the galaxy appear at different positions with respect to the stars at different times of the year?
roy
- 61
5
votes
2 answers
Why do some stars have a negative parallax?
I am constructing a Hertzsprung-Russell diagram for stars within some radius around Pleiades and have repeatedly come across stars that have negative parallaxes. For example,…
jm22b
- 764
4
votes
1 answer
Parallax angle calculation
I'm trying to understand how the parallax angle is calculated.
I alredy read this explanation.
So we got that distance between the sun and the star is d = tan(α) * 1 AU.
That said my doubt is about the angle α. We can calculate this based on the…
Isky
- 161
4
votes
3 answers
How to account for the movement of stars during measurement of parallax?
In my GCSE physics class today I was doing revision for my upcoming GCSEs, and we came to parallax measurements, as before my teacher explained that two measurements are taken six months apart as the Earth moves around the sun.
My question is, as my…
3
votes
0 answers
3D movie optics mathematics
I get the idea that we use two polarized light sources and a parallax rendered film such that the objects seem to resemble true parallax in our eyes once it passes through the polarized glasses, but I'm confused as to why the 3D effect is still…
Skyler
- 1,989
3
votes
1 answer
Measuring parallaxes from the moon
If one were to measure star parallaxes from the moon, what (if any) changes would you have to make compared to someone making the calculation from earth? What about on another planet in our solar system?
user56829
- 47
2
votes
0 answers
What's the relation between the parallax distance and the luminosity distance?
i have read that Riess and his team are able to measure $H_0$ from supernovae calibrated using Cepheid in a model independent way.
from what i have gathered they find the absolute luminosity of Cepheid $M_c$ with the parallax method and a bunch of…
Alucard
- 299
2
votes
2 answers
Parsec confusion
parsec is defined as the distance at which average radius of earth's orbit around sun would subtend an angle of 1''(second of arc). But suppose im looking at this star when earth is on one side of the sun, now six months later earth is on the other…
sanya
- 97
2
votes
3 answers
How to find transverse component of star's velocity given its proper motion and distance from observation point?
If $\mu$ is the proper motion of a star in arcseconds per year, and $d$ is the star’s distance from us, then the transverse speed, $v_t$ will be
$$v_t=d\sin\mu$$
For small motions (assumed for this question) $\sin\mu\approx \mu$
Barnard’s…
BLAZE
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2
votes
4 answers
Why do we have to wait half a year to measure stellar parallax
To measure distance of astronomical objects, often we may use parallax, the angle it makes with the earth-sun and trigonometry to determine the distance.
The thing I don't get is why do we need to sweep out at least half a circle and then look at…
John Hon
- 2,384