The Drake Equation is a famous formula for determining the probability of detecting alien civilizations. It is simply a set of simpler probabilities multiplied together to get a very small number.

`N = R* • fp • ne • fl • fi • fc • L`
• N = The number of civilizations in the Milky Way galaxy whose electromagnetic emissions are detectable.
• R* =The rate of formation of stars suitable for the development of intelligent life.
• fp = The fraction of those stars with planetary systems.
• ne = The number of planets, per solar system, with an environment suitable for life.
• fl = The fraction of suitable planets on which life actually appears.
• fi = The fraction of life bearing planets on which intelligent life emerges.
• fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
• L = The length of time such civilizations release detectable signals into space.

Source: space.com

It's occurred to me that the the same formula can be applied to other areas of life, such as the probability of being able to stargaze on any given night. To honor the original equation, I'll call this equation the Darke (geddit?) equation:

`N = clear • seeing • location • moon • weekend • family`
• N = The probability of being able to conduct astronomical observations on any given night..
• clear = The fraction of nights that are clear.
• seeing = The fraction of nights where seeing is adequate.
• location = The fractions of nights one has access to the observing site.
• moon = The fraction of nights where the Moon is sufficiently dim.
• weekend = The fraction of nights that are NOT followed by an early morning.
• family = The fraction of nights where family commitments do not prevent stargazing.

This formula results in a tiny fraction. Multiply this by 365.24 to get your Darke Number, the number of nights you think you might be observing in a year.

Here is a Darke Number calculator to enable you to quickly and scientifically calculate how hopeless your situations is:

```N = clear(
0.05
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1.0
) • seeing(
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1.0
) • location(
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)
• moon(
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) • weekend(
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) • family(
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1.0
)```