Yay! I'm so excited to see Halley!

The Sun had been waiting many years to see his friend, Halley the comet.



She was finally coming to visit him today!

When Halley finally reached the Sun, he was filled with joy!

He could not wait to hang out with his friend Halley.

Sadly, Halley only had enough time to say "Hello!" Then, she left!

The Sun would have to wait many more years to see her again.

What's wrong?

The Sun was sad and confused why Halley has such quick visits, then leaves for so long.

He got to see his other friends, the planets, all the time, so where was Halley going?

The Sun decided he was going to find out why Halley the comet was so different from his friends the planets.

He got out his notebook, and he was ready to investigate!

First, he wrote down his question, "Why does Halley the comet move differently than my other friends, the planets?"

In his notebook, he wrote down how Halley moves really fast when she gets close to him, but slows down a lot as she gets further away.

On the other hand, the planets mostly keep the same speed as they move around him.

"Interesting," he thought.

The Sun thought that maybe Halley moves so fast because she is so small. He began writing about Halley's size in his notebook.

He wrote: "Halley is much smaller than my friends the planets. She looks like a tiny pebble compared to the planets! Maybe she moves so quickly because she is so little and not heavy."

The Sun also noticed that Halley moves downward when she leaves, but his friends the planets, like Earth and Mars, move on the same level around him.

He wrote this observation down in his notebook. He felt like this was very important to note.

The Sun was finding a lot of evidence for how Halley is different from his friends the planets, but he still wanted to know why!

The Sun saw the Earth passing, and wanted to ask him for help.

"Why do you, Mars, Mercury, Venus, Jupiter, Saturn, Neptune, and Uranus all go around me at the same level, but Halley moves downwards?" he asked.

"That's because we are all on a line called the ecliptic that was made when the Solar System formed," the Earth answered.

The Solar System

Halley's orbit

Suddenly, the Sun remembered when the Solar System was formed billions of years ago. He remembered being flattened into a disk.

It started to make sense to him. If the Planets all were moving on a disk except Halley, she probably was not here when the Solar System was formed. Or, maybe she was, but an object hit her and she got pushed out of the disk!

Pull

Pull

Now that the Sun knew why Halley went downward, he had to find out what made her go so far away for so long.

The Sun noticed that whenever she did come to visit, he felt like he was pulling her in. He also noticed that he does this with the planets too. It feels like he is using a force on them, even though he is not trying to.