How to convert arcsec to steradians

[Teenion]

If I know the angular size of the object in arcsecs let's say r, how can I convert it into steradians size? is it just that the size in steradians is r²?

 

[Orodruin]

You don't, not unless you know the shape of the object. An arcsecond is an angle and a steradian is a solid angle, they are different things. It is like asking how to convert a length into an area.

 

[Teenion]

You don't, not unless you know the shape of the object. An arcsecond is an angle and a steradian is a solid angle, they are different things. It is like asking how to convert a length into an area.

I know its spherical object (I should have mentioned it in my first post)..
Yeah, converting is not a good word for what I want to do.. Better question would be How can I obtain the size of the spherical object in steradians if I know the angular size in arcsecs.

 

[haruspex]

I know its spherical object (I should have mentioned it in my first post)..
Yeah, converting is not a good word for what I want to do.. Better question would be How can I obtain the size of the spherical object in steradians if I know the angular size in arcsecs.

Since you are working with arcsecs, I assume we're discussing very small angles. If the subtended angle (of a diameter) is theta and the distance from the observer is R, what, roughly, is the visible area? Divide that by R² and you have the steradians.