An example of a simile in popular science writing:
"…interstellar gas… contains clouds of tiny dust particles, which are a great nuisance to the observational astronomer because they produce a sort of fog that limits his vision whenever he [sic, or she] tries to look deep into the Milky Way. Forty years ago it was thought that when we look out at the Milky Way we see the whole Galaxy. But we now know that this view is hopelessly wrong. The fog I've just mentioned cuts down our vision so much that, instead of out being able to see the whole of the Galaxy, we see only about a tenth part of it…
If you want to look toward the centre of the Galaxy you should seek out the great star clouds that lie in the constellation of Sagittarius, the Archer. But you will not see the centre; it is for ever [!] hidden from us by the fog we have just discussed…Radio waves can easily penetrate the fog, whereas light cannot."
Fred Hoyle (1960) The Nature of the Universe (Revised ed.), 1960
Read about examples of science similes
Note: that what is introduced as a simile ('a sort of fog' ) then becomes employed as a metaphor without being marked as figurative ('The fog I've just mentioned…', '…hidden from us by the fog…', '…penetrate the fog…').
Arguably, 'clouds' is here used metaphorically as the interstellar dust is not an aerosol like the water droplets found in 'actual' clouds, and even if that seems pedantic, stars do not form clouds n the conventional sense. (The word cloud, for its present meaning was derived metaphorically because some clouds looked like lumps of earth or rock – 'cluds' in the Old English spelling.)
