The Orbit of Halley’s Comet

Did you know that Halley’s Comet – the most famous reoccurring comet last seen in 1986 – is on its way back from deep space? But no need to pull out your telescope just yet, it won’t be near Earth until 2061.

So why am I that interested in Halley’s Comet if we can’t see it for another 37 years? Because when I was 6 years old, I vividly remember going out on a cold night in 1986 to attempt to locate the comet with my mom and my brother. 

Oh, and did I mention that I wrote a middle grade series about a girl who was named after Halley? So you see, I’m just a little intrigued by this comet that comes around every 76 years.😉

The occurrence of Halley’s Comet in history wasn’t always understood until Isaac Newton and Edmund Halley determined it had an elliptical orbit around the sun as opposed to a circular orbit like some planets.

The comet has two points in its orbit – one that comes close to the sun called it’s perihelion (which occurred February 9, 1986) and one that is farthest point from the sun called it’s aphelion (which just occurred December 9, 2023).

To understand this elliptical orbit, check out this simple activity.   

Here’s what you need: a cardboard box or board, 8-1/2 X 11″ paper, pens, 2 straight pins, a string tied in a loop about 2″ long

Here’s what you do:

1. Fold the paper in half and draw a line down the center.
2. Measure the center line and two points 0.5″ away from the center line
3. Place the paper on top of the cardboard and insert the pins in the two points
4. Loop the string around the two pins and carefully trace the path guided by the pins 
5. This path will look like a flattened circle which is an ellipse
6. Next place the pin in the center mark and trace it around. This makes a circle.
   
7. Move the two pins further out to about 1.5″ from the center line and trace this ellipse. It will be flatter than the first. This shape is what Halley’s orbit resembles. 

What’s the science: The closer the two pins (or foci) are together the more it resembles a circle. Earth’s orbit is not a circle and neither is Halley’s Comet – but Halley’s orbit’s foci are further away than Earth. Interestingly, the closer Halley gets to the sun’s foci and gravitational pull, it speeds up until heads out to it’s second foci beyond Neptune.

To learn more about Halley’s Comet you can follow along with me in this book written just following the 1986 passage of Halley’s Comet.

I can’t wait to share with you the story – and prequel to the series – that I am writing about the last time Halley’s Comet was visible from Earth in 1986…💫