On the night of the winter solstice, December 21, Jupiter and Saturn will appear to be together in the night sky, shining together as one celestial body.
The event has been called by many the “Christmas Star”, referring to the Star of Bethlehem in biblical history, according to Christian tradition, in which the three sages were guided by the brightness of the star to the place of the Nativity.
But beyond religious belief, professional and amateur astronomers around the world have prepared their telescopes to scan the sky and witness a celestial event whose interest is comparable to the expectations generated by a total solar eclipse.
The planetary coincidence will produce what on the night of the 21st will appear to be a much brighter star, in what is expected to be one of the greatest conjunctions of modern times. Consider this: these planets will look closer to each other since the time of Galileo Galilei in the seventeenth century.
Jupiter and Saturn will be only a tenth of a degree away from our perspective or about a fifth of the width of the full moon. These planets, the two largest in our solar system, are widely separated from each other, about 4.5 times the average distance between Earth and the sun, which is considered an astronomical unit.
Stephen Hummel, a dark-skinned astronomer at the McDonald Observatory in West Texas – led by the University of Texas at Austin – answers a few questions about this phenomenon, the best ways to view it, and some tips to further enhance the experience.
What will happen on the night of December 21?
There will be a conjunction between Jupiter and Saturn. And that means they will appear very close to each other. Every time two things appear next to each other in the sky, in astronomy we call it a conjunction, and conjunctions in general are not very rare. They appear quite regularly, between planets and the moon and other objects. But this conjunction between Jupiter and Saturn will be very close, closer than it was in 1623, and the last time it was visible was in the thirteenth century. They will appear to some as a large, bright, star-like light source, and others may still solve the two planets. For some, it will look like a large source of bright light, like a star, but others will be able to differentiate the two planets. But, of course, these are two planets.
(Note: the planets do not produce their own light, they only reflect sunlight.)
What can people expect to see?
(The planets) will appear to be close to each other in the sky, (on the horizon) to the southwest (United States), just as it gets dark, dusk is the best time to see it, even in polluted cities a light. Jupiter is bright, so it won’t be a problem to see it, and Saturn will be right above it. Saturn is a little weaker than Jupiter, so it may be harder to notice at first, but it still shouldn’t be too much of a problem for most people.
The conjunctions are common and this is due to the way our solar system works. The earth revolves around the sun and also Jupiter and Saturn. It takes Jupiter about 12 years to orbit the Sun, and Saturn is approaching 30 years. And that means that every 20 years, they seem to overlap or, technically, when Jupiter appears to be above Saturn from our perspective. So physically, there are many millions and millions of miles away. And if you’re somewhere else in the solar system, you wouldn’t see it. Only from the perspective of the earth do we see this conjunction. It means they look very close to each other here, but they’re actually very far apart.
Will everyone in the world see the same?
Basically yes. From a technical point of view, the moment of the closest conjunction appears at a certain moment that not everyone will see, this is the closest real and true point, but you could not differentiate it. As long as I’m not too close to the poles, most of the world will be able to see it.
Do you need special equipment to see the conjunction?
No special equipment is needed to view the planets. Jupiter and Saturn are generally seen with the naked eye. However, if you want a better experience, it is recommended to use at least some binoculars. With binoculars you can see (even) the months of Jupiter. You will not be able to see Saturn’s rings with binoculars, but you will be able to appreciate better (the conjunction).
But if you use a telescope, it could be quite spectacular. You will be able to see both planets at the same time at a fairly large magnification, which is not something you can normally do. In other words, you can have an image of the telescope showing both the rings of Saturn and the moons of Jupiter and all the edges of Jupiter in the same photo, side by side. The problem is that because it will appear at the bottom of the sky, about 15 degrees above the horizon when it gets dark (in Texas), the quality of the magnified view may not be very good, because the lower the sky the see more (interference from) atmosphere.
How rare is this phenomenon?
There is a conjunction between Jupiter and Saturn, generally every 20 years, but they are usually not so close. Every few hundred years, one appears that is very close. The last one that was actually visible was in 1226 and there was another in 1623, but it was too close to the sun to be seen very well. So it is very rare that they are so close … this is certainly the closest (conjunction) in our times.
ITWill the stars shine brighter than usual?
Jupiter and Saturn are brighter than most stars. Jupiter in particular is bright, but the planets will not appear brighter. They will not change much visually, it’s just that you can see two of them next to each other. That night, Jupiter will be the brightest object in the twilight. Saturn is about the brightness of an average star. Most stars are easy to see without trying too hard, but (Saturn’s brightness) will be several times weaker than Jupiter.
Do you have any advice to better observe the night sky?
To see better at night, practice using avoided vision, as it is much more sensitive to light. You can see things much, much more blurred. You can practice this by looking at the sky and trying to find the faintest star you can and look at. When you do this, you will see it and it will disappear and when you look elsewhere, it will reappear; this is an avoided vision. It takes a little practice, but it really helps a lot when it comes to finding smaller things, especially if you are dealing with pollution in the city, it can be really helpful.
Can you use a mobile phone to capture the conjunction?
It’s not impossible. I guess you could try, but it would be very, very hard. You need a tripod (standard base), at least. Jupiter and Saturn can probably be seen with a camera phone, but I don’t know how far they will be during the conjunction. So it’s more of a no than a yes.
If you use a phone or a help screen to find the connection, make sure you have it in red mode, with a red filter, or in night mode; many mobile phones and other devices already have it. Red light does not activate your daylight as much as white or blue light, which could destroy your night vision adaptation.
Transmitting the image of the McDonald’s observatory
The McDonald’s Observatory will host a live broadcast of the conjunction on December 21 at 18:00 on its YouTube channel, with live images captured by its telescopes. In addition, there will be a discussion with Kevin Mace and Frank Cianciolo, members of the observatory’s visitor center, and astronomer Stephen Hummel.
This is the McDonald Observatory League
Marisol Chávez is a freelance journalist from El Paso and Ciudad Juárez and a contributor to Al Día and The Dallas Morning News.