- #36

#### collinsmark

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Summary::Like how is it possible that Earth was just perfectly made for life?

It seems impossibly unlikely that Earth would be able to harvest life. I also heard that the moon is exactly 400 times smaller than the sun and 400 times the distance from each other, which makes solar eclipses possible.

It doesn't need to be exact. All that's necessary is for the angular diameter of the moon to be greater than or equal to the angular diameter of the Sun (or star in question). It can be "greater than." It doesn't need to be equal or "exact."

For example, here is a couple of simultaneous eclipses happening on Jupiter (eclipses happen on Jupiter very frequently; they're really nothing unusual). I took this photo last year with my backyard telescope.

Figure 1. Jupiter, Ganymede, and Io. 2020-08-15 04:33.7 UT

How could a coincidence this major even happen? I also heard that the moon is getting farther and farther away from the sun, so eventually solar eclipes won't even be possible, so what are the odds that the only time sentiment beings are on earth, is the time solar eclipes happen. Like just how could that even happen?

The Moon is not gradually getting farther away from the Sun any more than the Earth is getting farther away from the Sun. I think you mean that the Moon is getting farther away from the Earth. This is true, but only by a 3.8 centimeters (1.5 inches) per year.

Whatever the case, eclipses are not unusual, and more to the point, the existence of life on Earth almost certainly has nothing particularly to do with eclipses.

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On a different note, this might be a good time to introduce the Drake Equation into this thread.

The Drake Equation is a contrived equation to calculate the number of civilizations in our galaxy with which communication might be possible. Again, it's a

*contrived*equation, not a derived one. So it's not particularly insightful on its own. But it does help with defining and compartmentalizing the different aspects involved, and should be relevant to this discussion.

[tex] N = R_* \cdot f_p \cdot n_e \cdot f_l \cdot f_i \cdot f_c \cdot L [/tex]

where:

[itex] N = [/itex] the number of civilizations in the Milky Way galaxy with which communication might be possible.

and,

[itex] R_* = [/itex] the average rate of star formation in our galaxy

[itex] f_p = [/itex] the fraction of those stars that have planets

[itex] n_e = [/itex] the average number of planets that can potentially support life, per star that has planets

[itex] f_l = [/itex] the fraction of planets that could support life that actually develop life at some point

[itex] f_i = [/itex] the fraction of planets with life that actually go on to develop intelligent life (civilizations)

[itex] f_c = [/itex] the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

[itex] L = [/itex] the length of time for which such civilizations release detectable signals into space

I won't go into the estimates for each component in this post. But I will say that our estimates of [itex] f_p [/itex] have gotten much larger within the last couple of decades.