# The meaning of angular extent

## Main Question or Discussion Point

Hi
I know the meaning of trigonometric parallax, but what is angular extent?
In a problem, it is stated that the true angular extent of semi major axis of the orbit is 7.61".
Is it different from parallax?
Thanks

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The angular extent is simply the angular size---i.e. how big it looks.

marcus
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Hi
I know the meaning of trigonometric parallax, but what is angular extent?
In a problem, it is stated that the true angular extent of semi major axis of the orbit is 7.61".
Is it different from parallax?
Thanks
the typical application of parallax is where the baseline is provided by OUR orbit around the sun.

It sounds to me as if you have a school problem in which there is a binary star or the star has a planet or something orbiting it.

So you are supposed to estimate the real size of a distant object (an orbit) given its angular size seen from earth.

the picture is turned around, the base of the long skinny triangle is out there.

With parallax the baseline is here at home. We get to look at the object from two different locations along the earth's orbit.

That seems like a difference.

Thank you very much! I got it.
so, if I know the distance to that binary or orbit, I know its linear size.

marcus