How do you measure an object's brightness?

[pipnina]

I'd guess stars are the easy objects to measure... but how would you go about measuring the brightness of an objects like the California nebula or the veil? Do you use normal cameras or spectroscopy? Do you need to take the reading from space or will the reading be accurate from the ground? Is it possible to create a brightness for different parts of an extended object or does the object have to be described as "mag 5 spread over 5x1.3 degrees" ?

Quite the question. I'm quite intrigued!

 

Thanks,

    ~pip

[scarp15]

Not at all sure how these measurements are determined. The Veil I believe is classified at Mag 7, though due to its large 3 degree spread, actual surface brightness is dim. Some facets are considered visually brighter than other segments (with of cause a filter), such as the Eastern Veil.  

[LukeSkywatcher]

I am purely an observing kind of guy. I dont give any thought as to the technical,scientific,maths of the universe (or even any gear i use to observe it with). I am simply an observer along for the ride.

Sorry, i know this doesnt help in any way.

[dph1nm]

On 2/4/2016 at 21:56, pipnina said:

I'd guess stars are the easy objects to measure... but how would you go about measuring the brightness of an objects like the California nebula or the veil? Do you use normal cameras or spectroscopy? Do you need to take the reading from space or will the reading be accurate from the ground? Is it possible to create a brightness for different parts of an extended object or does the object have to be described as "mag 5 spread over 5x1.3 degrees" ?

Quite the question. I'm quite intrigued!

 

Thanks,

    ~pip

You measure the surface brightness, in magnitudes per square arcsecond. Yes, this can be done from the ground and yes you do it with normal imaging. You use stars of known brightness to calibrate the image - you can then convert counts from the camera directly into magnitudes. So you just go to any part of the nebula you want and measure the number of counts you get in an area of known size ...

NigelM

[pipnina]

4 minutes ago, dph1nm said:

You measure the surface brightness, in magnitudes per square arcsecond. Yes, this can be done from the ground and yes you do it with normal imaging. You use stars of known brightness to calibrate the image - you can then convert counts from the camera directly into magnitudes. So you just go to any part of the nebula you want and measure the number of counts you get in an area of known size ...

NigelM

Thank you! Was really interested and you cleared things up, cheers!

[Ruud]

Here's a wikipedia article on the bolometer. It has a few links to other devices for measuring the energy carried by radiation.