Explosion

One megaton on the surface, as close to physics as a vacuum allows. The parts physics would not allow are listed at the bottom.

Step by step

• Countdown. Ten seconds, read over the radio with Apollo-style Quindar tones.
• Flash and fireball. A plasma ball up to about 1 km wide that turns transparent within seconds.
• Crater. The ground itself changes: a crater about 500 m across and 100 m deep, shaped like the Sedan nuclear test crater. Molten rock on its floor glows and cools.
• Ejecta. Rock leaves at hundreds of metres per second, up to 1.5 km/s. With no air to slow it, it flies in clean arcs and forms a cone-shaped curtain. Boulders tumble and bounce.
• Ground shock. A fast deep wave, then a surface wave at about 110 m/s that lifts dust and can lift you. The Moon keeps ringing for about a minute.
• Radiation. After the gamma flash, the suit dosimeter starts clicking.

Aliens within about 3 km do not survive. Up to about 8 km they are injured.

Added for the game

A mushroom cloud, the red light that follows it and the heat shimmer cannot exist without air. They are there by choice, because a nuclear blast without them did not look like one.

Speed

Settings → Game → Explosion speed runs the blast 1× to 5× (2× by default; 1× is real time). The rocket and the countdown always run in real time.