Tonight, Saturn and Jupiter will appear close enough to each other that they may look like a single bright star in the sky. This is the first time in hundreds of years this has happened -- and it won’t happen again in many of our lifetimes.
Student Reporter Olivia Streeter talked with Nick Rae, the Planetarium Educator at the Peoria Riverfront Museum, about this unique astronomical occurrence.
Olivia Streeter: What can you tell us, Nick, about the astronomical event that is happening on December 21?
Nick Rae: There's a planetary conjunction on the winter solstice, coincidentally, December 21, when Jupiter is going to be closer to Saturn than it has been since 1623. And they will be close enough that probably some people will perceive them as just one object low in the southwest setting a little after six o'clock or so.
The conjunction this year is going to feature Jupiter, which with already looks like the brightest star in the sky. It'll be fascinating. Like I said, really, really close to Saturn. And that's the result of Jupiter going around the Sun faster than Saturn, and catching up to Saturn.
OS: So what is the significance of this event in particular? What makes this event so special?
NR: So this will be the closest the two planets have been since 1623. And back then when they got that close, they were kind of close to the sun in the sky. So probably nobody saw it back then.
The last time anybody saw these planets this close was probably back in 1226, hundreds of years before the telescope was invented. So this is a really special conjunction.
OS: Some individuals would call this event the appearance of the "Christmas star." Where did this phrase come from?
NR: The Christmas star that's in the Bible, people have tried to come up withnatural explanations of some event in the sky that people may have seen back at the time.
And that may be referring to, for example, a comet or a star that exploded as a supernova for a planetary conjunction where a couple of bright planets were close enough together in the sky that maybe they looked like one really bright object, but there's no actual convincing case for any specific hypothesis. So in a sense, it's not explained what the the Christmas star or the Star of Bethlehem could have been in a natural way.
OS: Should we try to get to the darkest spot possible to view something like this?
So this is actually one you don't have to go anywhere super dark. The real trick is just getting a view low towards the southwest. It'll be relatively low in the sky early in the evening. So it's possible trees or houses might be in the way. So you'll want to maybe drive somewhere if you need to, or walk somewhere where where you have a clear view of the horizon in the southwest, but it'll be shortly after sunset.
Roughly the sun is setting, I don't know, 4:30 or so in the evening. And so by 5:30, twilight is basically over. And you'll be able to see even before twilight's over. You'll be able to see Jupiter and Saturn again every night low in the southwest and then getting closer and closer each night and getting a bit lower and lower each night as well.
Just get somewhere where you see low to the southwest early in the evening, because they'll be setting. By 6:30, they'll probably be below the horizon.
OS: Great. Well, is there anything else we should know about this occurrence?
So, try to go out each night. That's clear early in the evening. And so you can see them, and you can watch them from night to night getting closer and closer. And, of course, you can imagine the actual 3D movements that are happening, with Jupiter orbiting the sun at a much faster rate than Saturn orbits the Sun, and it's catching up. And it'll be passing by Saturn. Jupiter's out there roughly half a billion miles away. Saturn will be twice as far away, about a billion miles away. They can sort of try to imagine it 3D while you're watching from our planet.
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