A once-in-a-lifetime event is happening tonight. I’m sure you’ve already heard about it. But I don’t know if anyone has really broken it down to explain just how special it is.
The “Christmas Star” will be visible tonight. This is when Jupiter and Saturn align in the night sky – shortly after sunset in the southwestern sky for North America – to make them appear a one star.
The ‘Great’ Conjunction
NASA – and other astronomical enthusiasts – call this The Great Conjunction. And it has a fair bit of history…
In 1610, Italian astronomer Galileo Galilei pointed his telescope to the night sky, discovering the four moons of Jupiter – Io, Europa, Ganymede, and Callisto. In that same year, Galileo also discovered a strange oval surrounding Saturn, which later observations determined to be its rings. These discoveries changed how people understood the far reaches of our solar system.
Thirteen years later, in 1623, the solar system’s two giant planets, Jupiter and Saturn, traveled together across the sky. Jupiter caught up to and passed Saturn, in an astronomical event known as a “Great Conjunction.”
NASA.gov
“You can imagine the solar system to be a racetrack, with each of the planets as a runner in their own lane and the Earth toward the center of the stadium,” said Henry Throop, astronomer in the Planetary Science Division at NASA Headquarters in Washington. “From our vantage point, we’ll be able to be to see Jupiter on the inside lane, approaching Saturn all month and finally overtaking it on December 21.”
The planets line up in a similar way about every 20 years. But they only get this close in the night sky every 400 years. And, according to astronomers, they only line up to be nearly on top of eachother like tonight every 800 years.
And before you say, “Well, if I miss it tonight, I can just see it next year when it is barely any different”
You can’t.
That is what the alignment will look like next year. They won’t be as close. Why not?
This happens because the planets are not orbiting the sun evenly. So the inner planets zip around the Sun while the outer planets take much longer to orbit.
Earth moves through the Solar System at about 30km/sec. Jupiter? Only 13km/sec. Saturn moves at about 10km/sec.
So, it takes time for all of the moving pieces to line up in the right way for the two planets to appear to be on top of eachother.
Keep looking up!
The Earth is getting a special visitor from the Asteroid Belt in January. And while it will be very close, don’t worry, it should stay far enough away not to bother life on this planet.
On January 25, 2021, Asteroid 2018BA3 will make a close cosmic pass to Earth. It will be about 0.00183au from Earth as is zings by.
That sounds super close. But it converts to about 170,000 miles.
Cosmically close! But actually not.
This asteroid is about the size of a house. So it won’t be visible by the naked eye. However, due to the way it will pass, if you have a reasonably strong backyard telescope, you may be able to see it after midnight.
It also helps that we will be passing by this asteroid as it crosses the plane of its orbit.
Neat stuff!
