Stargazers will be treated to a rare alignment of seven planets on 28 February when Mercury joins six other planets that are already visible in the night sky. Here’s why it matters to scientists.
Peer up at the sky on a clear night this January and February and you could be in for a treat. Six planets – Venus, Mars, Jupiter, Saturn, Uranus and Neptune – are currently visible in the night sky. During just one night in late February, they will be joined by Mercury, a rare seven-planet alignment visible in the sky.
But such events are not just a spectacle for stargazers – they can also have a real impact on our Solar System and offer the potential to gain new insights into our place within it.
The eight major planets of our Solar System orbit the Sun in the same flat plane, and all at different speeds. Mercury, the closest planet to the Sun, completes an orbit – a year for the planet – in 88 days. Earth’s year, of course, is 365 days, while at the upper end, Neptune takes a whopping 60,190 days, or about 165 Earth years, to complete a single revolution of our star.
The different speeds of the planets mean that, on occasion, several of them can be roughly lined up on the same side of the Sun. From Earth, if the orbits line up just right, we can see multiple planets in our night sky at the same time. In rare events, all the planets will line up such that they all appear in our night sky together along the ecliptic, the path traced by the Sun.
Mercury, Venus, Mars, Jupiter and Saturn are all bright enough to be visible to the naked eye, while Uranus and Neptune require binoculars or a telescope to spot.
In January and February, we can witness this event taking place. The planets are not exactly lined up, so they will appear in an arc across the sky due to their orbital plane in the Solar System. During clear nights in January and February, all of the planets except Mercury will be visible – an event sometimes called a planetary parade. On 28 February, though – weather permitting – all seven planets will be visible, a great spectacle for observers on the ground.
“There is something special about looking at the planets with your own eyes,” says Jenifer Millard, a science communicator and astronomer at Fifth Star Labs in the UK. “Yes, you can go on Google and get a more spectacular view of all these planets. But when you’re looking at these objects, these are photons that have travelled millions or billions of miles through space to hit your retinas.”
While fascinating to observe, do such alignments have any impact here on Earth? Or might they have a use for increasing our understanding of our Solar System and beyond?
In fact, says Millard, “it’s just happenstance that they happen to be in this position of their orbits”. And while there have been suggestions from some scientists that planetary alignments might cause impacts on Earth, the scientific basis for most of these claims is weak or non-existent.
In 2019, however, researchers suggested that planetary alignments could have an impact on solar activity. One of the main outstanding questions about the Sun is what drives its 11-year cycle between periods of peak activity, known as solar maximum (which we are currently in), and periods of weakest activity, solar minimum. Frank Stefani, a physicist at Helmholtz-Zentrum research centre in Dresden-Rossendorf in Germany, believes the combined tidal forces of Venus, Earth and Jupiter could be the answer.
While the tidal pull of each planet on the Sun is extremely small, Stefani says that when two or more of the planets line up with the Sun – known as a syzygy – they might combine to cause small rotations inside the star, called Rossby waves, which can drive weather events.
“On Earth, Rossby waves cause cyclones and anticyclones,” says Stefani. “We have the same Rossby waves in the Sun.” Stefani’s calculations showed that the alignments of Venus, Earth and Jupiter would cause a periodicity to solar activity of 11.07 years, almost exactly matching the length of solar cycles that we see.
Not everyone is so sure about the idea, with some noting that solar activity can already be explained by processes within the Sun alone. “The observational evidence suggests that the planets directly causing the solar cycle just doesn’t happen,” says Robert Cameron, a solar scientist at the Max Planck Institute for Solar System research in Germany, who published a paper on the subject in 2022. “There’s no evidence of any synchronisation.”