An alert reader submitted this
question via Facebook:
“[W]hat the heck is up with: ‘One
light year, is the distance light, moving at 299,792 kilometres per second
travels in a year, or about 10 trillion kilometres.’?”
A most excellent question. <bowing head> Let us parse.
Using the inexplicably outmoded but
still useful technique of sentence diagramming (which I have always itched to investigate but never before had
opportunity), we find that the simple subject is "light year" (sometimes
written as “light-year," which I would advocate here, for reasons you will
shortly understand), and that it has been modified by the adjective "One.”
So far, so good.
The simple predicate is also easy-peasy--it's
"is." Hooray!
No, don’t argue, children. There is
no other choice. In this sentence "travels" is obviously a noun, although
more specifically it is the second half of the compound noun “second-travels”
and (who was the copyeditor???) therefore in dire need of a hyphen. I
don't pretend to know what "second-travels" are, but would venture to
guess that this compound noun designates the trip one makes to a specific spot
after having visited it once (and only once) before.
Similarly, although the word “moving”
appears here in classic verb form, it is unquestionably being employed as an
adjective (i.e., “causing strong emotion”). Unfortunately, a little
interference seems to have inserted itself between this adjective and the noun
that it modifies. This may be random noise, probably interstellar. (If you
listen to a sample
here, you can see how easily this might happen.)
I suspect that the noun being
modified by “moving” is the aforementioned “second-travels” (don’t they sound
like fun?), although one might argue that it is, instead, the adjective grouped
within this phrase (“kilometres per”)—modified in turn by the quantifier “299,792”
(which strikes me as rather a long way to go for a second-travel, or even for a
first!)—which would mean that it is functioning here more as a noun. But for
the sake of argument (’cause we love that stuff), we’ll diagram it as an
adjective.
Oh, the diagram! Let’s get back to
it.
Our next discovery is a delightful
one: We have a subject complement! (I love when that happens.) Here, it is “the
distance light.” (We may have to start docking that copyeditor’s pay, as this
would have been more immediately graspable had this additional compound noun also been hyphenated: “distance-light.”) Yet again, I am not clear on
the meaning. Fortunately, my purpose is to decode the grammar, not to divine
the sense. I’m an editor, not an astrophysicist. But I rather imagine a
"distance-light" is a kind of sidereal lighthouse. Quite poetic!
What we have next is a somewhat
unfortunate pile-up of appositive phrases. I am not sure how “distance-light” (sing.)
can be equated with “second-travels” (pl.), but the structure of this sentence
demonstrates very clearly that these terms correspond. “Second-travels” is
modified quite spectacularly, first (as mentioned earlier) by “moving at,” then
by “kilometres per” (which are in turn quantified by “299,972”) and finally by
the prepositional phrase “in a year.”
At this stage, we are offered an
alternative. Instead of equating “distance-light” with “second-travels,” we are
given the option (such is the function of the “or”) of drawing a
parallel with “kilometres” (modified by “trillion,” quantified by “10,” in turn
qualified by “about").
How very mysterious! I have no clue
how 299,972 kilometres can be equated with 10 trillion kilometres. We may need to
consult a science person—preferably someone who’s good with this deep-space stuff.
Judging by the grammar alone, we
find that the secret may lie in the sneaky insertion—heavens, a third (or is it fourth?) unhyphenated compound,
this time an adjective! (Time to fire that copyeditor!)—of “per.” And that gives
us all the information we need. Indubitably, in the world of astrophysics, “kilometre
[n.]” does not equal “kilometre-per [adj.]”.
Lastly, we discover that . . . Well,
we discover, rather shockingly and anticlimactically, not only that this
sentence makes no sense at all, but that it fails to conclude! It’s true. Just
look at the diagram, above.
On the whole this is a rather good
thing, as not only have we run out of patience, but our diagram has run off the
page.
But wait. It has struck us like a lightning bolt (or a meteorite) that there is an
easier solution. What happens if we commit a simple comma shift? How much
confusion (and silliness) might have been avoided!
“One light year is the distance light,
moving at 299,792 kilometres per second, travels in a year, or about 10
trillion kilometres.”
Given my druthers, I might have rewritten this
sentence (actually, there's no “might” about that), but now, all of a sudden, it makes
sense.
See how important it is to keep track of your commas?
Thank you, alert reader!