All planets seem to line up in the sky towards the end of February
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All the planets of our solar system line up for parade in the night sky at the same time. This extraordinary celestial event will see the dispersed sky of seven planets visible in what is known as a great planetary alignment.
The eight planets of our solar system orbit the sun in the same plane, because they were all formed at the origin of the same debris disc Around the sun. The line of the sun traces in the daytime sky, called the ecliptic, aligns with this plane, so when the planets appear in the sky, they all appear along the ecliptic. It is not a perfect line of planets, because their orbits are slightly tilted, but it is quite close.
This is never more apparent than during a planetary alignment. An alignment comprising all the planets, with the exception of Mercury, takes place in mid-January. Uranus and NeptuneBeing the most distant planets, will only be visible by a telescope, but you may be able to spot others with the naked eye.
The great alignment, including Mercury, will only occur for a few evenings around February 28, according to your location. The seven planets will be briefly visible just after sunset, extending into an arc through the sky.
When the sky is completely dark, mercury and Saturn will have sunk under the horizon, with Neptune and Venus following shortly after. The best time to spot the planets will be in the hour that followed the sunset, while all except March, Jupiter and Uranus will be close to the horizon. These three will continue to drag for most of the night, but locating three planets in the sky is not as rare as finding the seven.
The main thing preventing such alignments from being visible all the time – apart from the weather – is the difference in orbital periods between the planets. Mercury, which is closest to the sun, takes about 88 days from the earth to finish an orbit, while Neptune, which is the most remote, takes almost 165 years of earth.
A large alignment is only possible when the planets are all relatively far from the sun, so they are visible at night, and all in the same half of the sky, so they can be seen at the same time. It is a remarkable orbital coincidence – sometimes there are several large alignments in a year, and sometimes several years pass without one.
In some respects, a planetary alignment is simply an optical illusion: the planets are always separated by millions or billions of kilometers, and if you could look at our solar system from the outside, you would never see them armed in a perfect line emanating from the sun. But for stargazers around the world, it's an excellent chance to see all the planets at the same time, carefully distributed in the sky.
