The impression of an artist of the solar system
Shutterstock / Vadim Sadovski
All the planets of our solar system line up in the night sky at the same time this week. This extraordinary celestial event will see the dispersed sky of seven planets visible in what is known as a large planetary alignment, or a “planetary parade”.
The eight planets of our solar system orbit the sun in roughly the same plan because they all have been formed from the same debris disc Around the sun. The sun line 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. As a general rule, only a few planets share the night sky, but an unusual alignment of the seven planets will be visible for a few evenings around February 28, according to your location.
The best time to watch is just after sunset, with a chance to see all the planets stretch in an arc through the sky, although all except March, Jupiter and Uranus will be close to the horizon. These three will continue to drag for most of the night, while the sky is completely dark, Mercury and Saturn will have sunk under the horizon, with Neptune and Venus following shortly after.
The main thing preventing such alignments from being visible all the time – apart from the weather – is the difference in orbital periods among the planets. The mercury, which is closest to the sun, takes about 88 days from the earth to finish an orbit, while Neptune, which is most the distant planet, takes nearly 165 years of land.
A large alignment is only possible when the planets are all relatively far from the sun, they are therefore visible at night, and all in about 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. A similar event should not occur before 2040.
“It's great to see the interest that the planetary parade generates,” says David Armstrong At the University of Warwick, United Kingdom. “Commitment to astronomy, the gaze to the sky and the appreciation of the wonder of our solar system are all fantastic, and I encourage anyone interested in taking the time to go out and see the planets with their own eyes if they have the opportunity in the coming days and a clear sky.”
Additional reports by Alex Wilkins
