Planetary “Alignments”

Ever so often, you hear news about planetary alignments in the sky, and there is a good reason for it – several of the brightest planets are appearing to be aligned in the sky, or IN LINE with each other so to speak.

Are they anything major or special – astronomically speaking? Not really. However, they are fun targets for wide angle astrophotography, and are easy to observe as one doesn’t need a telescope to enjoy them, and they often have windows that last more than a few days for one to observe thus one won’t feel too bad if they miss out on a night.

Here we will talk about what’s actually happening and why they appear the way they do.

I cannot tell you how many visitors came up to the Observatory and ask me about a “planetary alignment” going on. This was especially during a notable ongoing one in the month of April 2022. Many people would just hear the words, not bother to look up when and how to observe it, and thus come up hoping to see it during the evening viewing hours only for me to tell them “sorry, it’s visible at 5am before sunrise!”

Either way, we know that events like these are easy to get attention, and people like me are happy to explain the truth behind how these “planetary alignments” work.

So What’s Going On?

Equinox days are represented by the blue line.

Remember that the Sun has a “path” across the sky which we call the Ecliptic. The planets also usually appear along this path at any given point, and it’s all due to each planet, including Earth, all having the same orbital plane with a few minor tilt differences in relation to the Sun. You can see an example of this in the following image.

Each planet in this picture has its own orbital “path” shown in red. Note the path of Venus as seen in this picture… this is due to the inferior orbit compared to Earth.

And BECAUSE they share that same orbital plane, they sometimes appear “in line” due to their respective orbital positions around our Sun as seen from Earth. They are not actually all “aligned” with Earth, nor in the same order in the Solar System as you see from Earth in these following pictures.

In late April of 2022, one could see four of the five naked eye planets in the morning sky. The images above are from April 20. While they do appear in line from Earth, in reality, here is the positions as they were in the solar system.

As you can now see… even though Jupiter appears closest to the Sun (or where it would be in the sky before sunrise), it’s actually “third” in that order in terms of distance, and neither Saturn nor Jupiter are in line with Venus or Mars. In reality, we see this formation because all four of these planets are on that side of the Solar System. As they continue their orbits, the four planets in the 4/20/2022 pictures will gradually shift in two ways – one from appearing closer or further from each other in the sky, and two – from being morning targets into becoming evening targets after a few months. If one sees a formation like this in the evening, then the same happens, only they will shift into morning targets a few months from then.

That should help explain to you what actually is going on, and how many of these so called “alignments” are not actually true alignments. But when you see three to four of them along the same side of the sky in a relatively tight order, we still enjoy the sight when they appear like jewels in a cosmic necklace, especially when the moon joins them as a centerpiece.

It’s even more rare when you have all five of the naked eye planets appearing on the same side, as that usually happens every half century or so on average, with the last time being in 2002, and the next time being on September 6, 2040. This is due to Mercury’s fast 88 day orbit and its closer position to the Sun making it difficult to spot in the sky on most nights.

If All 8 planets were truly in line with each other in the Solar System – like how one sees in left-right diagrams in the order of Sun through Neptune:

  1. Observers on the day side of Earth would see Mercury and Venus transit across the Sun simultaneously…
  2. Observers on the night side of Earth would see Mars, Jupiter, Saturn with the naked eye, plus Uranus and Neptune, all appear at opposition (rise at sunset, cross meridian at local midnight, set at sunrise), and appear so tightly positioned that one could cover all of them with their thumbs!
  3. NOTHING like this has ever happened in recorded history!

Will we ever see all of them truly align together in the sky at the same time? No. They all have different orbital tilts in respect to one another, and all have different orbital speeds. The next time you’ll see all 7 planets in the same 180 degree side of the sky won’t be until the year 2492, and even then you’ll need a telescope to observe two of them. So when you happen to see all 5 naked eye planets on the same sky you’re still just as gifted!

HOWEVER – Are there ever celestial events when two or more planets are actually perfectly in line with each other AND earth?

Jupiter and Saturn seen with the naked eye on 12/21/2020

Yes!

But we don’t call them alignments – we call them conjunctions!

They too happen somewhat frequently but it’s those nights when they appear super close together that are much more rare – thus more special to check out. Check out this post all about conjunctions, or check out my page on the Great Conjunction of 2020 – a once in a lifetime conjunction I got to experience.

Would it be nice to see all five naked eye planets “truly aligned” together in the sky as seen from Earth? Of course!

They just wouldn’t appear to form a long line in the sky like you have seen in the images, they’d appear to form an extremely tight group of “bright stars” and form perhaps a small five sided shape for a few nights.

There are also instances where Mercury and/or Venus are perfectly in line with our Sun and Earth… we call them transits! And they are much more rare than planetary conjunctions!

If anything, enjoy them for what they are, and keep looking up!

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