Venus

Venus Swing is the route where Ultimate Cycle Catcher first lets go of Earth and re-centres the camera on the Sun. Venus is a good place for that lesson, because it moves noticeably faster than Earth does.

Earth's twin, up close

Venus is almost the same size as Earth, about 12,100 kilometres across compared with Earth's 12,700, and it is the planet that comes closest to us. There the resemblance ends. Its thick carbon dioxide atmosphere creates a runaway greenhouse effect that keeps the surface at around 465 °C, hotter than Mercury, under a pressure about ninety times Earth's at sea level. Clouds of sulphuric acid hide the surface completely from ordinary telescopes, which is why it was first mapped by radar.

Venus also spins very slowly and backwards compared with most planets. One rotation takes about 243 Earth days, longer than its year.

An orbit inside ours

Venus orbits the Sun at about 72% of Earth's distance and completes a lap in about 225 days. Being closer to the Sun, it moves faster along its orbit, about 35 kilometres per second compared with Earth's 30. In the game's Sun-centered view you can see this directly: Venus gradually pulls ahead of Earth on every lap, so the cycler's swings in and back out are timed against two planets moving at different speeds.

Launch windows to Venus

Because Venus gains a full lap on Earth only every so often, the alignment that makes a cheap transfer possible repeats about every 584 days, a little over a year and seven months. A minimum-energy transfer from Earth to Venus takes roughly five months, following half of an ellipse that touches Earth's orbit at one end and Venus's at the other.

Interestingly, five of those synodic periods add up almost exactly to eight Earth years. That near-resonance means the pattern of Earth–Venus alignments, and the position of Venus in our evening and morning skies, repeats on an eight-year cycle.

Gravity assists past Venus

Venus is one of the most useful planets in the solar system for gravity assists. A spacecraft that flies close to Venus can gain or lose a large amount of speed relative to the Sun without burning fuel. Missions to Mercury and to the Sun's neighbourhood have used Venus flybys to fall inward. Surprisingly, missions to Jupiter and Saturn have also used Venus: swinging inward first and then past Earth again can end up flinging a spacecraft outward more cheaply than a direct launch.

The game's Venus Swing route borrows this picture: the cycler dives in to Venus, swings back out to Earth, and does it again, before the camera returns to Earth for the last leg.

Why change the camera?

Once a spacecraft leaves Earth's neighbourhood, the Sun's gravity dominates its motion, so engineers switch to describing it relative to the Sun. When the game makes the same switch, Earth stops being a fixed point and begins to travel along its own orbit. Your rings still close at the right moment; it is only the background motion that suddenly looks different. Learning to ignore it is one of the main skills the game asks for.

Useful numbers

• Distance from the Sun: about 108 million km (0.72 of Earth's).
• Orbital period: about 225 days.
• Earth–Venus synodic period: about 584 days.
• Minimum-energy transfer time from Earth: about 5 months.
• Surface temperature: around 465 °C.

Continue to Mars, or return to Earth and the Moon.