Absolute and apparent magnitude

In summary, absolute and apparent magnitude can be measured in any photometric band, and it's important to specify which band is being used. While absolute magnitude does measure the intrinsic power output of an object, it is still specific to a certain band and is not necessarily measuring all wavelengths.
  • #1
mmssm
7
0
is that both of absolute and apparent magnitude counts only visible light?
since i found some books said absolute magnitude counts luminosity instead of intensity, where luminosity includes also the non-visible frequencies.

thank you!
 
Science news on Phys.org
  • #2
Welcome to PF mmssm!

mmssm said:
is that both of absolute and apparent magnitude counts only visible light?

No, you can define a magnitude in any band (range of wavelengths). In fact, magnitude is something that only makes sense IF you specify which in which photometric band that magnitude was measured. Usually a band is defined by using a filter that admits only a certain range of wavelengths, so that that is the range of wavelengths that is measured. For instance, one traditional photometric system uses three filters that define three different bands: U, B, and V (for ultraviolet, blue, and visible), each of which is centered on a different wavelength. You then have to be specific about whether you're talking about U-band, B-band, or V-band magnitudes.

Many other photometric bands exist as well. For instance in the near to mid-infrared you have the I, J, H, and K bands. You can measure the magnitude of an object in anyone of these bands.
mmssm said:
since i found some books said absolute magnitude counts luminosity instead of intensity, where luminosity includes also the non-visible frequencies.

thank you!
It's true that the absolute magnitude is a measure of the intrinsic power output (luminosity) of an object, but it's NOT true that you're measuring that output over all wavelengths. Just like the apparent magnitudes that I discussed above, absolute magnitudes are always specific to a particular photometric band, and you have to specify WHICH band it was measured in when you state an absolute magnitude.

If you do measure the intensity of a source over all wavelengths, then this is called the "bolometric" intensity , and you can define a corresponding "bolometic" magnitude that is the magnitude when all wavelengths are taken into account. However, this is usually hard to measure (especially from the ground, since not all wavelengths make it through the atmosphere).
 

What is the difference between absolute and apparent magnitude?

Absolute magnitude is a measure of the intrinsic brightness of an object, while apparent magnitude is a measure of how bright an object appears to an observer on Earth.

How is absolute magnitude calculated?

Absolute magnitude is calculated by measuring the amount of light an object emits and adjusting for its distance from Earth.

What is the significance of absolute magnitude?

Absolute magnitude allows scientists to compare the true brightness of objects, regardless of their distance from Earth, providing insight into their physical properties and evolution.

How is apparent magnitude measured?

Apparent magnitude is measured by comparing the brightness of an object to a standard reference point, such as Vega or Sirius.

What factors can affect the apparent magnitude of an object?

The apparent magnitude of an object can be affected by its distance from Earth, its size, and the amount of light it emits. Other factors, such as atmospheric conditions and light pollution, can also impact its apparent magnitude.

Similar threads

  • Astronomy and Astrophysics
Replies
2
Views
2K
  • Astronomy and Astrophysics
Replies
8
Views
2K
  • Astronomy and Astrophysics
Replies
2
Views
2K
  • Classical Physics
2
Replies
40
Views
4K
Replies
4
Views
4K
Replies
4
Views
1K
  • Astronomy and Astrophysics
Replies
3
Views
2K
Replies
1
Views
1K
Replies
2
Views
4K
  • Introductory Physics Homework Help
Replies
3
Views
590
Back
Top