1F30C (Milky Way)

wiki

the biggest size (and oldest) emoji depicted

weirdly, most often an external view with us deep within it

all forms are ambiguous/ unsatisfactory

cf night with stars, cityscape at dusk, bridge at night

1F30B (volcano)

wiki


Mount Fuji is a volcano due for eruption

since the plot device is already overused, symbolic meanings seem more useful-- person ready to explode, pot overflowing

1F30A (water wave)

any body of water

cf potable-water symbol, sweat drops

c1830

1F309 (bridge at night)

distinctly a suspension bridge [wiki]

possibly Tokyo's Rainbow Bridge (1993) or Japan's Pearl Bridge (1998)

NYC's Brooklyn Bridge (1883) or San Francisco's famous Golden Gate Bridge (1937)

1F308 (rainbow)

symbolically tolerance of diversity

(are those supposed to be clouds below, or land?)

the artist's palette emoji also suggests a range/choice of colors

folklore imagines a pot of gold
Judy Garland imagined heaven/utopia

real rainbows always have the red on the outside (and the sky is usually much darker outside the rainbow than inside it)

1F307 (sunset over buildings)

equally sunrise

1F306 (cityscape at dusk)

equally at dawn
no visible sun