What does “...the moon blocks sunlight from the Earth from space” mean?
It means we're talking about that the moon preventing sunlight from hitting the Earth (solar eclipse) as seen from the perspective of space.
In order to avoid the “from ... from ...” construct, what is an alternative phrasing?
“You may think you can picture a solar eclipse, but you haven't seen it from space.”
(I've basically just replaced “the moon blocks sunlight from the Earth” with “solar eclipse”)
In general, what's the essential relationship, if there is any, between the objects of the two from[s] in such a construct?
They both refer to a source of some kind. Within this particular concept of prevention (the first “from”), there is the idea of rescue (away) from a dangerous point of origin. With the second “from”, the source in question is the position of our perspective—from which we see.
For more detail, read on:
We've all seen pictures of what a solar eclipse looks like from our perspective, but what does it look like when the moon blocks sunlight from the Earth from space.
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I've included the beginning of the sentence in question because it's key to understanding the meaning of the part you've quoted. There's also a helpful sentence after that one:
In the image, the shadow cast by the moon is pictured off the coast of Alaska.
And the caption of the image:
Different perspective: An eclipse is seen from space - the shadow of the Moon can be seen on the Earth just off the coast of Alaska in 2012
From this context, it should be easy to see that the author is trying to write about a solar eclipse as seen from space. To avoid this awkward construction, in which the two juxtaposed instances of “from” refer to different things, the author might have instead written:
We're all familiar with the image of the moon blocking the sun from our earthly view, but what does a solar eclipse look like from space?
There are probably even clearer ways to write this, but in my example, I've preserved the meaning of each instance of “from”. The first refers to blocking sunlight from hitting the Earth, the second indicates that the images provide a view from space. These are different senses of the word. Out of the following, the first refers to prevention (#8) and the second refers to a point of view (#5):
from “frəm”
preposition:
- indicating the point in space at which a journey, motion, or action starts.
"she began to walk away from him"
- indicating the distance between a particular place and another place used as a point of reference.
"the ambush occurred 50 yards from a checkpoint"
- indicating the point in time at which a particular process, event, or activity starts.
"the show will run from 10 to 2"
- indicating the source or provenance of someone or something.
"I'm from Hartford"
- indicating the date at which something was created.
"a document dating from the thirteenth century"
- indicating the starting point of a specified range on a scale.
"men who ranged in age from seventeen to eighty-four"
- indicating one extreme in a range of conceptual variations.
"anything from geography to literature"
- indicating the point at which an observer is placed.
"you can see the island from here"
- indicating the raw material out of which something is manufactured.
"a varnish made from copal"
- indicating separation or removal.
"the party was ousted from power after sixteen years"
- indicating prevention.
"the story of how he was saved from death"
- indicating a cause.
"a child suffering from asthma"
- indicating a source of knowledge or the basis for one's judgment.
"information obtained from papers, books, and presentations"
- indicating a distinction.
"the courts view him in a different light from that of a manual worker"
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