Seven Planet Line Up 2022
The planets in our Solar System. Credit: NASA

Seven Planet Line Up 2022

09/06/2022Written by Catherine Muller

From the middle to the end of June 2022, cast your eyes to the morning sky to see a spectacular parade of the planets

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Observing the seven planet line up

Observing the seven planet line up
How the sky will appear on the morning of 24 June from Leicester, with five of the seven planets visible with the naked eye. Credit: Stellarium

The seven other planets in the Solar System will be parading across the morning sky together during the latter half of June. Just before sunrise, in the eastern sky, Mercury, Venus, Mars, Jupiter and Saturn will appear in alignment. These will all be visible with the naked eye. Uranus and Neptune, the two planets farthest from Earth, will also be visible, but require binoculars or a telescope to be seen. And on 24 June, the waning crescent moon will join the showcase, slotting in between Venus and Mars. Being able to see these planets aligned in the same part of the sky is a rare phenomenon, but the planets can be viewed individually throughout the year. Each one unique – there is something exciting to observe about all the other planets in the Solar System.

Mercury at greatest elongation

Mercury at greatest elongation
Diagram showing greatest elongations of an inferior planet such as Mercury. Credit : Wmheric

Mercury is quite the elusive planet- its proximity to the Sun means it is often washed out by our star’s incredible brightness and is difficult to see. Therefore, the best times to observe Mercury are when it appears farthest from the Sun on the dome of the sky. These are known as the greatest elongations and occur when Mercury is positioned at a tangent to Earth in its orbital path. On 16 June 2022 Mercury will reach greatest western elongation when it will be visible as a morning object in the eastern sky, just before the Sun rises. Elongations are measured in degrees east or west of the Sun, and on 16 June, Mercury will appear 21˚ from the Sun. Either side of this greatest elongation, Mercury will still be visible for a few days in the morning sky.

Phases of Venus

Phases of Venus
Diagram showing how the phases of Venus can be seen from Earth. Credit: Public Domain

Throughout the year, Venus alternates between being visible in the morning and the evening sky. This led to some ancient astronomers believing they were seeing two separate bodies in the sky. These two different ‘stars’ even had names, Phosphorus and Hesperus. To add to the confusion, when observed through a telescope, at times, parts of the disk of Venus appeared to be missing. Thanks to the observations of Galileo Galilei, it was discovered that Venus was just one planet and goes through phases much like the Moon.

Venus’ orbit of the Sun is closer than the Earth’s, so it completes one orbit much faster than Earth does (225 days in comparison to our 365.25). As a result, sometimes Venus is on the other side of the Sun from Earth. When this happens, from Earth’s view, Venus is fully lit by the Sun. This is the equivalent of a full moon. As Venus approaches Earth, we see less of its dayside as its phase begins to change. Eventually, we see nothing but an illuminated crescent, as Venus reaches its closest approach to Earth. It takes 584 days to go through one complete cycle of Venus’ phases- this is the amount of time it takes the planet to overtake Earth in its orbit.

 

Canali on Mars

Canali on Mars
Surface of Mars drawn by Schiaparelli. Credit: Public domain

With the development of larger telescopes and observatories throughout the world in the 1800s, scientists were able to study the planets in our Solar System in greater detail than ever before. The observations of one of these scientists, the Italian Giovanni Schiaparelli, accidentally popularised the idea that there was intelligent life on Mars.

In the late 1800s, Schiaparelli observed channels on Mars and named them ‘canali’. This name resulted in the misinterpretation that there were actually man-made canals on Mars, akin to the Suez Canal that was completed not that long before, in 1869. The idea was picked up by many influential scientists of the time, including Percival Lowell, who decided these canals were built by Martians to bring water from the polar caps to the equatorial regions.

The theory of these man-made canals has been subsequently disproved – they were optical illusions that resulted from the poor-quality telescopes of the time. In 1965, NASA’s Mariner 4 became the first spacecraft to reach Mars and sent back 22 photos of the planet’s surface to Earth. These photos confirmed that Mars was a dusty and dry world.

Galilean moons of Jupiter

Galilean moons of Jupiter
Jupiter and three of the four Galilean moons, seen through an amateur telescope like Galileo’s Credit: NASA

As the largest planet in our Solar System, Jupiter can be observed with the naked eye and has been known since ancient times. However, it wasn’t until 1610, when Galileo looked to the night sky, that we began to find out more about the Jovian system.

Using a small, homemade telescope, Galileo noticed three ‘stars’ within proximity to Jupiter that were moving in the wrong direction relative to the background of stars. After a week of observations, and the discovery of a fourth of these objects, Galileo concluded that they were not stars, but moons orbiting Jupiter. This proved to be a ground-breaking observation. The discovery provided evidence that not everything in the universe revolved around Earth, as was believed at the time. Scientists now believe that Jupiter has 79 moons, but these four Galilean moons remain some of the most interesting worlds in the Solar System, and some of the easiest to observe from Earth with a telescope.

 

Observing Saturn's rings

Observing Saturn's rings
A view of Saturn’s rings when its southern hemisphere was tilted towards Earth, 2004. Credit:NASA

When observing Saturn with the naked eye, it is not possible to see what the planet is known for – its incredible rings. A small telescope is required to see them. However, the view of the rings you get may not be the same each time you look to the sky.

This is a result of the tilt of Saturn’s axis by 26.7°, so the rings are not always on the same plane as planet Earth. In fact, Earth travels through the orbital plane of Saturn’s rings every 13-15 years. As a result, we spend half of the time observing the rings from the south, and the other half observing them from the north, when Saturn’s northern hemisphere is tilted towards Earth. When Earth does find itself in the same planes as the ring, they almost seem to disappear entirely, thanks to how thin they are (only 100m thick compared to the 270,000km ring width).

We are next due to cross the ring plane on 23 March 2025.

Blue hue of Uranus

Blue hue of Uranus
The featureless blue-green globe of Uranus Credit: NASA

In 1781, William Herschel discovered Uranus, making it the first planet to be found with the aid of a telescope. When observed, the face of Uranus appears quite plain, unmarked by any distinctive surface features. From Earth, Uranus’ most distinguishable characteristic is its blue-green hue. Uranus owes its colour to the gaseous methane present in its upper atmosphere. When sunlight reaches Uranus, the red wavelengths of light are absorbed by the methane, while the blue light is reflected, causing the planet to appear an azure colour. In 1986, the Voyager-2 probe flew past Uranus, confirming what we’d seen on Earth in more detail. Since the flyby of Voyager 2, however, no spacecraft have returned to Uranus. This has led to the call from prominent scientists to organisations such as NASA and ESA to prioritise the creation of a probe to be sent to this icy world.

Neptune and its spots

Neptune and its spots
The Great Dark Spot on Neptune’s surface, taken by Voyager 2 Credit: NASA

After Voyager 2’s flyby of Uranus, it reached Neptune in 1989. Upon arrival, the probe discovered a swirling storm the size of Earth on Neptune’s southern hemisphere. It was known as the Great Dark Spot with wind speeds reaching over 2000 kilometres per hour, the fastest known winds in the Solar System.

The Great Dark Spot is something of a mystery to scientists, however. In 1994, the Hubble Space Telescope photographed Neptune in an attempt to learn more about the storm but found it had disappeared! Astronomers theorise that the spot has either been covered up or completely vanished. The Great Dark Spot is not the only storm on Neptune, and these other storms also appear to have short lifetimes. This peculiar behaviour is something scientists are still trying to understand.

While Neptune is too far away to be viewed with the naked eye, it will be possible to observe the planet using a small telescope as part of the seven planet line up in June 2022.

About the author: Catherine Muller is a Space Communications Presenter at the National Space Centre.