ATRONOMY – ATROPHOTOGRAPHY & IMAGING (40) CALCULATOR
Extinction Coefficient
A precise tool.
What is the Extinction Coefficient & How does it work?
Atmospheric extinction describes how the Earthβs atmosphere dims starlight as it passes through. The amount of dimming depends on the amount of air mass the light traverses, which in turn varies with the observerβs altitude above sea level.
At sea level the extinction coefficient (kβ) is measured in magnitudes per airmass. As you ascend, the atmospheric column above you becomes thinner, and the extinction coefficient decreases roughly exponentially with altitude, following the scale height of the atmosphere (H), typically about 8β―km.
The relationship can be expressed as k = kββ―eβ»Κ°α΄΄, allowing astrophotographers to predict how much atmospheric dimming will affect their exposures at a given site. Knowing k helps in planning exposure times, selecting filters, and calibrating photometric measurements.
k = k_{0}\,e^{-\frac{h}{H}}
k = extinction coefficient at altitude (mag/airmass)
k_{0} = seaβlevel extinction coefficient (mag/airmass)
h = altitude above sea level (m)
H = atmospheric scale height (m)
k_{0} = seaβlevel extinction coefficient (mag/airmass)
h = altitude above sea level (m)
H = atmospheric scale height (m)
Parameters
Result
β
Frequently Asked Questions
What is the extinction coefficient at sea level?
The extinction coefficient (kβ) at sea level is typically measured in magnitudes per airmass.
How does extinction coefficient change with altitude?
As altitude increases, the atmospheric column above decreases, causing the extinction coefficient to decrease roughly exponentially.
What factors affect atmospheric extinction?
Atmospheric extinction is influenced by factors such as air mass, humidity, and the observer’s altitude above sea level.
Can you explain the scale height in relation to atmospheric extinction?
The scale height describes how quickly the atmosphere thins with altitude, affecting the rate at which the extinction coefficient decreases.
How do I calculate the airmass for a given observation?
Airmass can be calculated using the secant of the zenith angle (the angle between the vertical and the line to the celestial object).
What is the practical use of knowing the extinction coefficient?
Understanding the extinction coefficient helps astronomers correct for atmospheric effects when measuring stellar brightness.
How does humidity affect atmospheric extinction?
Higher humidity can increase atmospheric extinction because water vapor absorbs more light, particularly in certain wavelength ranges.
Results are for informational purposes only and do not constitute professional advice.