Worlds like our own, indeed most worlds, have Fire Suns. They transmit heat and light to our worlds, because our worlds are naturally of darkness. We are of darkness, built to be animated by light.
Tellurine does not have a Fire Sun. Tellurine is a place of incandescent mist and fog, and it has an Earth Sun. Their sun transmits sensation and solidity to their planet.
There is plenty of light and heat to go around in Tellurine’s glowing ether, even at night. But at night it is impossible to grasp. You fall through walls, your feet swim in the sidewalk, and you feel nothing, just a great cotton numbness all around. But when the sun shines on the mists, they suddenly acquire substance. First very soft in the early morning, where you could still poke your finger through the average streetlamp. Then as the sun climbs high and transmits its solidness, things get harder, clay walls are baked into brick, pools of airy water evaporate into wetness, and the streets turn to steel. Earth seeps into everything it can reach. Only spots under shady trees remain soft, patches made of sponge.
As evening comes, things melt and waver. Night falls, stone recedes, the brick walls turn back to clay and then to mud, and you drift off just as the rest of the landscape around you does the same. It is only next morning, when the bed beneath you solidifies enough to wake you up, that you can set your feet back on solid ground again.
The Tellurines themselves follow the same rules as their world, they are wraiths at night and stone in the day. People retire for the day not because it becomes dark, but because they can no longer grip the tools they need to do work. Night shift workers either do jobs that require no physical interaction or they work by the artificial solidity of a desk lamp, which shines a narrow band of substance onto a patch of their desk, just the amount to make paperwork tactile enough to shuffle and fill out.
Under the Earth Sun, they live their public lives, and they turn to love in the insubstantial night. Shy Tellurine lovers pass their hands through each others’ breasts, kissing without ever touching, occupying the same space in desperate embrace. They feel each others’ warmth but not their skin. It is only the boldest among them that kiss in Solid Sun. It is a terror at first. They feel each other be too real, far rougher than they imagined each other to be in their dreams. They fear it but delight in it, knowing that in this revealing, embarrassing substance they have learned they can love each other even at their hardest.