Exploring The Planets

Mercury

Mercury is the closest planet to the sun, it is a bare, airless and rocky world. Because it lies between the Earth and the Sun, it shows pronounced phases, like the Moon. The main challenge for photographing Mercury is that it never gets far from the sun although sometimes it can be seen low above the horizon just before dawn, or after sunset. Mercury passes across the face of the Sun (a 'solar transit') on average every six or seven years, but the mechanics of its orbit means that such transits usually happen in pairs a couple of years apart, followed by a longer gap before the next one. The most recent transits were in 2016 (when the picture below was taken) and 2019.

Venus

The next planet is Venus, its dense atmosphere of carbon dioxide causes a runaway greenhouse effect that means its surface is hot enough to melt lead.  These temperatures combined with clouds of sulphuric acid mean visiting space probes can only survive for a short time. Images taken in ultra-violet light  show these clouds in a striking planet-wide V-shape. Despite being Earth's closest neighbour these challenges mean it is far less visited than Mars. Venus also transits the sun, but much more rarely, and like Mercury it shows phases, but it does move further away from the sun and so is easier to observe - often being the brightest 'star' in the sky.

Earth

We are all familiar with our home planet, but naturally it's not possible to take the sort of images of Earth that orbiting spacecraft can get. The photo below shows one way to cheat - it shows part of the Earth's shadow on the moon during a Lunar eclipse.

Mars

Mars is the next planet, and the best explored of solar system bodies after the Moon. It appears as a bright orange 'star' - its blood red colour giving it a historical association with war. The timing of its orbit mean that it comes closest to the Earth roughly every eighteen months, with the distance of closest approach varying so sometimes its disc appears as large as Jupiter's. Like the Earth, Mars has distinct seasons with polar caps of water and carbon dioxide ice. Though its atmosphere of carbon dioxide is very thin, it can still whip up planet-wide dust storms that can hide most of the details visible under better conditions.

Jupiter

Further out and beyond the asteroid belt lies Jupiter. This gas-giant planet is mostly hydrogen, and is a great subject for photography as its appearance is constantly changing. It rotates in just seven hours so storms and other features pass rapidly across its disc and its four Galilean moons, Io, Europa, Ganymede and Callisto are easily seen in their constant dance around the planet. The image below shows its characteristic pattern of bands, the famous Red Spot - a storm bigger than the earth - and also its closest moon Io at top right, casting its shadow on the planet below.

Saturn

Saturn is a remarkable and unforgettable sight. Another gas giant, but slightly smaller than Jupiter, its banded rings tilt towards and away from us as it slowly orbits the sun going from wide open to almost invisible every fifteen years. The bands on Saturn's disc are less marked, but still visible. Occasionally small white storms can be seen, and hints of a strange dark, hexagonal storm that appears to be permanently fixed at its north pole are captured.

Uranus

Rather smaller than Jupiter and Saturn, Uranus is an 'ice giant' composed largely of frozen gases mostly methane and ammonia, rather than hydrogen. It has a pale blue-green colour, and it is rare to be able to capture any markings on its surface. Oddly it's axis of rotation is tilted so that it appears to 'roll' along its orbit. It has several fairly bright moons that can be imaged by taking longer than usual exposures that cause the planet itself to 'blow out'.

Neptune

Since Pluto was demoted to the status of a 'minor planet', Neptune is the most distant planet from the sun. Like Uranus, it is an ice giant with very little detail visible in most photographs, and only slightly larger. Its atmosphere has a distinct blue colour, partly caused by methane in its atmosphere. In some photos pale clouds can be seen streaking across the blue. Longer exposures reveal its brightest moon, Triton. After the Earth's Moon, Triton is the largest moon compared to its planet in the solar system.