Swapna Krishna

Sep 9th 2022

Rare Planetary Alignments: What is a Conjunction?


In late June, five planets aligned in the Earth’s night sky: Mercury, Venus, Mars, Saturn and Jupiter. These planets travel through our dark sky along the ecliptic, which is the path the sun travels in our sky over the course of a year (a result of the Earth orbiting the sun). Occasionally, these planets travel close to one another as seen from the Earth. Astronomers call this occurrence a conjunction.

Every once in a while, something very special happens — multiple planets come together in the same part of the sky for a planetary alignment. But exactly how often do the planets align? Here are the ins and outs of planetary alignment, as well as how best to observe the planets from Earth without a telescope.

What Is Planetary Alignment?

The planets in the night sky aren’t always visible. They rise and set over the course of the night, and sometimes when they’re in conjunction with the sun, they aren’t visible at all.

Planetary alignments are, essentially, optical illusions. In reality, within space, the planets are nowhere near each other. This lining up is specific to how these planets are seen from the Earth. Venus and Jupiter will be next to each other in the Earth’s night sky, but in reality they’re 430 million miles apart.

Observing Planets With the Naked Eye

Planets are among the brightest objects in our night sky, reflecting the light of the sun. There are technically six planets visible from Earth without a telescope; they include Mercury, Venus, Mars, Saturn, Jupiter, and Uranus, though Uranus is only visible under perfect viewing conditions. Venus is the second brightest object we can see at night (after the moon, of course) followed by Jupiter. Mars and Mercury are fifth and sixth on the list, preceded by Sirius, the dog star.

If you see a bright object in the night sky and aren’t sure whether it’s a planet or a star, there’s one easy way to tell: Planets don’t twinkle. Stars are very distant pinpricks of light; because of that distance, their light is more affected by Earth’s atmosphere. This makes it appear as if they are twinkling. Planets, on the other hand, appear as steady bright objects in the night sky.

The planets are also distinct colors. Mercury is yellow, while Venus is white. Mars appears red-orange in our night sky, while Jupiter is a white-orange. Saturn, like Mercury, is yellow.

Seeing the Planetary Alignment

To see the most planetary alignment, you need find the perfect spot. In the case of the late June alignment, because Mercury was so close to the horizon, you would have needed to be in a location in the northern hemisphere that had a completely flat view of the sky when facing East.

Timing is also important when it comes to viewing alignments. In late June, the planetary alignment was easiest to see in the hour before sunrise.

It’s important to note that Uranus and Neptune were also be part of this alignment. If viewing conditions were absolutely ideal, it was possible to see Uranus between Mercury and Mars. Neptune was not be visible with a naked eye, but could be seen with a telescope.

How Often Do the Planets Align?

As Live Science explains, planetary alignments aren’t common — but they aren’t rare either. The last time that this kind of five-planet alignment happened was in 2020. Before that, it was 2016 and 2005. In this particular alignment, the planets lined up in the following order (starting at the horizon going north in the sky): Mercury, Jupiter, Venus, Mars and Saturn.

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