A rare celestial phenomenon seen only once every few years will light up the sky this week.
Stargazers will be able to spot six of the planets in our solar system lining up in the sky in a ‘planetary parade’. Four of the planets – Mars, Jupiter, Saturn and Venus – will even be visible to the naked eye.
So if you look up at the sky and spot four more eye-catching ‘stars’, they might actually be planets! And those with a telescope will see Neptune and Uranus join the party. NASA says Venus and Saturn will be visible in the southwest just after sunset, with Jupiter overhead and Mars in the east completing the planetary display.
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Planetary alignment is an astronomical term used to describe when planets gather closely on one side of the Sun at the same time.
Although planets are technically always ‘aligned’ because they orbit the solar system on the same plane (called the ecliptic), it’s rare to see four or five planets at once, NASA says.
An alignment of five or six participating planets is classed as a ‘large’ planetary alignment, which only happens once every few years.
The highly-anticipated planetary alignment has been dubbed a ‘planetary parade’ -Credit:Getty Images
When to see the ‘planetary parade’
The earliest, and possibly the best, time to spot the four planets in the sky is 6pm UK time on 18 January, Dr Dan Brown, an astronomy expert at Nottingham Trent University, told The Sun. The planets will sit approximately 20 degrees above the horizon.
The good news is that this isn’t your only chance to see the parade. They should be visible from 5pm to 9pm that night, but 6pm might just offer the best viewing conditions.
But don’t fret if you miss it (or if bad weather affects visibility). The Royal Observatory says the best night to view the four-planet parade is January 21, from just after sunset until around 9pm.
This is when all planets visible in the line have the smallest arc in the sky. The moon will also be in its last quarter phase, meaning the evening skies will be darker, according to Live Science.
The planetary parade should be visible in the evening sky until around the end of February, according to The Planetary Society.
Other exciting celestial events this week
Mars is having a particularly special month as it reaches opposition this week, shining at its biggest and brightest for more than two years.
Opposition means the planet is opposite the Sun in the sky, meaning Mars will appear big and bright: at its best for viewing.
Mars will reach opposition at 3am UK time on 16 January. Although this happens about every two years, NASA says this year it will be closer than average, making it appear bigger than usual.
The planet was closest to Earth at 2 pm UK time on 12 January. It was 5.3 light-minutes away at a distance of 0.642 astronomical units (96,084,099 kilometers).
Four planets will be visible to the naked eye and six with a telescope -Credit:Getty Images
Shortly after Mars reaches opposition, there will be an exciting conjunction between Venus and Saturn where the planets come within about 2 degrees apart in the sky! This will happen on the night of 17-18 January.
Highly anticipated planetary alignments
The most noteworthy planetary alignments are those where many planets are grouped uncharacteristically close together.
Here are three of the most anticipated alignments, according to Star Walk, but don’t hold your breath – they’re not anytime soon.
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September 8, 2040 – five naked-eye planets (Mercury, Venus, Mars, Jupiter, and Saturn) will align in the sky
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March 15, 2080 – six planets (Venus, Mercury, Jupiter, Saturn, Mars, and Uranus) will be visible in the morning sky. It will feature the ‘great conjunction’ of Saturn and Jupiter
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May 19, 2161 – all Solar System planets, including the Earth, will gather on one side of the Sun
Could we ever see an eight-planet parade?
All eight major planets – Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune – could sadly never make an aligned appearance in our night sky.
According to Jean Meeus’ book Mathematical Astronomy Morsels, all eight planets will line up to within 3.6 degrees of sky every 396 billion years. Our universe is only 13.7 billion years old, so we’ll sadly never see a full planetary alignment.