Seven planets will align in the sky next month. That’s what it really means

Stargazers will be treated to a rare alignment of seven planets on February 28, when Mercury joins six other planets already visible in the night sky. Here’s why it matters to scientists.

Look 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. For one night only in late February, they will be joined by Mercury, a rare alignment of seven planets visible in the sky.

But such events aren’t 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 one orbit – one year for the planet – in 88 days. Earth’s year, of course, is 365 days, while at the upper end, Neptune takes 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, some of them may line up on roughly the same side of the Sun. From Earth, if the orbits line up just right, we can see many planets in our night sky at the same time. In rare events, all the planets will line up in such a way that they all appear in our night sky together along the ecliptic, the path followed by the Sun.

Mercury, Venus, Mars, Jupiter and Saturn are all bright enough to see with the naked eye, while Uranus and Neptune require binoculars or a telescope to spot.

In January and February, we can witness this event. The planets are not exactly aligned, 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 planets except Mercury will be visible—an event sometimes called a planetary parade. On February 28, though – weather permitting – all seven planets will be visible, a wonderful spectacle for observers on the ground.

“There’s something special about seeing 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 to Google and get a more spectacular view of all these planets. But when you look at these objects, these are photons that have traveled millions or billions of miles through space to hit your retina.”

While fascinating to observe, do such alignments have any impact here on Earth? Or could they have a use in increasing our understanding of our Solar System and beyond?

In fact, says Millard, “it is by chance that they are in this position of their orbits.” And while there have been suggestions by some scientists that planetary alignment may occur cause impacts on Earththe scientific basis for most of these claims is weak or non-existent.

In 2019, however, researchers suggested that planetary alignments can have an impact on solar activity. One of the major unsolved 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, the solar minimum. Frank Stefani, a physicist at the Helmholtz-Zentrum, a research center in Dresden-Rossendorf in Germany, suggested that 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 planets line up with the Sun – known as a syzygy – they can combine to cause small rotations within the star, called Rossby waveswhich can trigger weather events.

“On Earth, Rossby waves cause cyclones and anticyclones“We have the same Rossby waves in the Sun.” Stephen’s calculations showed that the alignments of Venus, Earth, and Jupiter would cause a periodicity of solar activity of 11.07 years, almost exactly matching the length of the solar cycles we see.

Not everyone is so sure about the idea, with some noting that solar activity can now only be explained by processes inside the Sun. “Observational evidence suggests that planets that directly cause the solar cycle simply don’t happen,” says Robert Cameron, a solar scientist at the Max Planck Institute for Solar System Research in Germany, who published the paper. on the subject in 2022. “There is no evidence of any synchronization.”

But there are other, far less controversial features of planetary alignments that certainly have an impact on us: their utility for scientific observations, especially in terms of exploring the Solar System.

Reaching the outer planets with a spacecraft is difficult because these worlds are so far away, billions of miles away, that it would take decades to reach. However, using the gravitational pull of a well-placed planet such as Jupiter to launch a spacecraft from the outside can reduce travel times dramatically, something no spacecraft has done better than NASA’s Voyager vehicles.

In 1966, a NASA scientist named Gary Flandro calculated that there would be one alignment of the four outermost planets – Jupiter, Saturn, Uranus and Neptune – in 1977 that would allow all four to be visited within a span of just 12 years, compared to 30 years if they were not aligned. This fortuitous alignment, which occurs only once every 175 years, led NASA to launch the twin spacecraft Voyager 1 and 2 in 1977 on a “Grand Tour” of the outer solar system.

Voyager 1 flew by Jupiter in 1979 and Saturn in 1980, avoiding Uranus and Neptune because scientists wanted to pass by Titan, Saturn’s fascinating moon, and could not do so without disrupting the slingshot effect.

“It worked fantastically,” says Fran Bagenal, an astrophysicist at the University of Colorado, Boulder in the US and a member of Voyager’s science team. “If Voyager 2 had left in 1980, it would have taken until 2010 to reach Neptune. I don’t think it would have gained support. Who would fund such a thing?”

It is not only within our Solar System that planetary alignments are useful. Astronomers use alignments to investigate many different aspects of the Universe, and none more so than in the discovery and study of exoplanets, worlds that orbit stars other than the Sun.

The dominant way to find such worlds is known as mode of transit: when an exoplanet passes in front of a star from our point of view, it dims the star’s light, allowing its size and orbit to be discerned.

Thanks to this method, we have discovered many planets in orbit around certain stars. Trappist-1, a red dwarf star located 40 light years from Earth, has seven Earth-sized planets that all pass the star from our point of view. The planets in that system actually are in resonance with each other – meaning that the outermost planet completes two orbits for every three orbits of the next planet within, then four, six, and so on. This means that there are periods where many planets in the system line up in a straight line, something that does not happen in our Solar System.

Using transit, we can study the existence of atmospheres on such planets. “If a planet with an atmosphere passes in front of a star, this alignment means that starlight passes through the planet, and the molecules and atoms in the planet’s atmosphere absorb light at certain wavelengths,” says Jessie Christiansen, an astronomer at Nasa’s Exoplanet Observatory. . Institute of Science at the California Institute of Technology.

This allows different gases such as carbon dioxide and oxygen to be identified. “The vast majority of our analysis of atmospheric composition is due to stretching,” she says.

Much grander arrays may allow us to probe the distant Universe, namely galaxy arrays. Observing galaxies in the very early universe is difficult because they are so faint and far away. However, if a large galaxy or group of galaxies passes between our line of sight and a much more distant early galaxy, its strong gravitational pull can magnify the light of the more distant object, allowing us to observe and study it. , a process called gravitational lensing.

“These are huge alignments across the scale of the universe,” says Christiansen. They are used by telescopes such as the James Webb Space Telescope to observe distant stars and galaxies such as the Milky Way. Earendelthe most distant star known from Earth. The telescope’s first light from the star came from the first billion years of the Universe’s 13.7 billion year history and was only visible due to gravitational lensing.

And then there are some newer uses of the alignments, such as searching for the existence of extraterrestrial life, in solar systems where exoplanets pass in front of each other from our point of view.

In 2024, graduate student Nick Tusay at Pennsylvania State University in the US used these alignments to look for any widespread communication being sent between the worlds of the Trappist-1 system, like how on Earth we send signals to planets like Mars in our solar system to talk to rovers and spacecraft. “Any time two planets are aligned it can be interesting,” says Tusay.

In this case, the search turned out to be short. But an alien civilization looking toward our Solar System could use similar alignments for the same purpose. While the planetary parade this month depends on your perspective – any two planets in our system can line up if you’re positioned at the right angle – it’s not impossible to imagine someone else on the other side, watching.

“Maybe another alien civilization could see this as an opportunity to conduct their own investigations,” says Tusay.

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