The exceptional convergence of planets observable in the Belgian sky these days: “It’s very rare, it happens about every twenty years”


This is exceptional: in the next few days, from Earth, we will see five planets of the solar system with the naked eye gathered in the same corner of the sky. “It’s called conjunction: a meeting of planets. The last of this kind occurred in 2004. It’s very rare, it happens about every twenty years, explains the astronomer Emmanuel Jehin (ULiège). You can see Mercury, which is the lowest, and then Venus, Mars, Jupiter and Saturn, which are aligned in the sky very early in the morning, before dawn. “

The planets of the solar system all revolve around the same plane around the Sun (the plane of the ecliptic), which means that at certain times, from the Earth, we can see the planets close to each other. “But to find them at the same time you need the right timing! It is very difficult to have Mercury with everyone else, because it is very close to the Sun. It was therefore necessary to wait until all the planets were in the same corner of the sky. The problem is that Jupiter takes ten years to circle the Sun; and Saturn, thirty! “Here, what is also exceptional, is that they are arranged in the same order as the natural order of their distance from the Sun (in the solar system, Mercury is closest to the Sun, followed by Venus, Earth, Mars and finally Jupiter and Saturn) .

Of course, if we could observe the solar system from afar, we would see that the planets are indeed scattered. Only the perspective from the Earth allows us to see an “alignment”. The phenomenon is visible between about 15 and 25 June from Belgium, but it is quite difficult to contemplate, like everywhere. “Mercury is hard to see these days, because it’s still very low on the horizon, you can’t see it until just before sunrise. Mercury is generally the hardest planet in the solar system to see. It is even said that Copernicus, the father of heliocentrism, which establishes that all planets revolve around the Sun, has never seen it in person, because it is very low. Next week, Mercury will be higher in the sky and therefore easier to see. “

The maximum tightening of the planets will occur on June 22. The advantage? This grouping can be observed from cities because the planets are relatively bright. City dwellers with balconies and in height will have an advantage because it is necessary to benefit from a clear horizon to the east. The ideal is to use binoculars to find Mercury more easily. “To see them all, it’s best to get up around 4 in the morning, about half an hour before sunrise, and look eastexplains Emmanuel Jehin. To take Venus as a reference point because it is very bright and therefore easy to see. Jupiter and Saturn arise first; Mercury and Venus, just before dawn. Venus shines brightly, Mars and Jupiter are quite bright, and Jupiter is a little dimmer. The lowest on the horizon is Mercury. “ The eight solar system objects (planets and Moon) will actually all be clustered on the west side of the Sun, but Uranus and Neptune are not visible to the naked eye (Neptune also requires a telescope or telescope). Such a grouping is also very rare; the next will be in 2124.


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