Exploring The Planets

Mercury

Mercury is the closest planet to the Sun — a bare, airless, rocky world baked by intense solar radiation. Because it lies between the Earth and the Sun it shows pronounced phases, much like the Moon, cycling from crescent to full as it orbits. The main challenge for observers is that Mercury never strays far from the Sun in our sky, appearing only briefly low on the horizon just before dawn or just after sunset. Occasionally Mercury passes directly across the face of the Sun in an event called a solar transit — these occur in pairs a few years apart, followed by a much longer gap. The most recent transits were in 2016 and 2019, with the next not due until 2032.

Venus

Venus is Earth's nearest planetary neighbour and the brightest object in the sky after the Sun and Moon — often visible in full daylight if you know where to look. Beneath its brilliant white clouds, however, Venus is a hellish world. Its dense atmosphere of carbon dioxide drives a runaway greenhouse effect, raising surface temperatures high enough to melt lead, while clouds of sulphuric acid make it deeply hostile to visiting spacecraft. Like Mercury, Venus shows phases as it orbits the Sun, and at its crescent phase it can appear surprisingly large through a telescope. Venus also occasionally transits the Sun, though far more rarely than Mercury — the most recent transit was in 2012 and the next will not occur until 2117.

Earth

We know our home planet well, but it is not something we can image from the ground in the way spacecraft can. One creative way to capture Earth in an astronomical image is during a lunar eclipse, when the Earth's curved shadow falls across the face of the Moon — a beautiful reminder that we live on a sphere travelling through space.

Mars

Mars is the most explored world beyond the Moon, and a fascinating target for amateur observers. It appears as a distinctly orange-red star in the night sky — its blood-red colour historically giving it an association with war. Mars comes closest to Earth roughly every 26 months, and the distance at closest approach varies considerably, with some oppositions bringing Mars much nearer than others. Through a telescope, the polar ice caps, dark surface markings and occasional planet-wide dust storms are all visible under good conditions. Like Earth, Mars has distinct seasons and a thin atmosphere — thin enough to be breathed only in imagination, but capable of whipping up enormous dust storms that can obscure the surface for weeks at a time.

Jupiter

Beyond the asteroid belt lies Jupiter — the largest planet in the Solar System and one of the finest sights in the night sky. This gas giant is composed mostly of hydrogen and helium and rotates remarkably quickly, completing one full rotation in just under ten hours. This rapid rotation means that surface features — cloud bands, storms and other details — visibly shift position during a single observing session. Jupiter's four large Galilean moons — Io, Europa, Ganymede and Callisto — are easily seen through binoculars and through a telescope can be watched moving night to night. The Great Red Spot, a storm larger than the Earth that has been raging for centuries, is one of the most iconic sights in planetary astronomy.

Saturn

Saturn is arguably the most spectacular sight in the Solar System and never fails to take the breath away — even for experienced observers. Like Jupiter it is a gas giant, though slightly smaller, and its magnificent ring system sets it apart from every other planet. The rings are tilted towards and away from us as Saturn slowly orbits the Sun, going from wide open to nearly edge-on and back again over a period of roughly fifteen years. The rings are currently tilting back open after reaching edge-on in 2025, so the view will improve year on year for some time to come. Saturn's cloud bands are subtler than Jupiter's but still visible, and occasionally bright storms erupt in its atmosphere.

Uranus

Uranus is classified as an ice giant — smaller than Jupiter and Saturn and composed largely of frozen gases including methane and ammonia rather than hydrogen. It has a distinctive pale blue-green colour caused by methane absorbing red light in its atmosphere. Uranus presents little surface detail even in large telescopes, but its several brightest moons can be captured with longer exposures. One of Uranus's most unusual characteristics is its extreme axial tilt — it is tipped almost completely on its side, so it appears to roll along its orbit rather than spin upright like the other planets.

Neptune

Neptune is the most distant of the eight recognised planets, lying so far from the Sun that it takes 165 years to complete a single orbit. Like Uranus it is an ice giant, with a deep blue colour caused by methane in its atmosphere. Little surface detail is visible from Earth, though long exposures occasionally reveal pale clouds streaking across its disc. Neptune's largest moon Triton is an intriguing world in its own right — it orbits in the opposite direction to Neptune's rotation, suggesting it was captured from the outer Solar System rather than forming alongside the planet.