Comet

From April 2020 through to July 2020, Comet ATLAS C/2019 Y4 will be passing close to the Sun and will often be visible in the night sky from the UK. When it is brightest, it might be possible to see it with your eyes without the need for binoculars or a telescope (although these might help you to see it clearer).

Comets are large balls of ice, rock and dust but you can think of them as large dirty snowballs that travel through the Solar System. For most of the time comets are invisible, but as they get closer to the Sun, the ice starts to heat up and turn into gas. The water vapour and dust released by the heating process forms an enormous tail that stretches out behind the central part of the comet, known as the nucleus. Find out more about Comets.

What shape are comets?

67P/ Churyumov-Gerasimenko.​ In 2014, the Rosetta spacecraft orbited this comet and the Philae probe robot landed on its surface. It has a diameter of approximately 4 km.

Image Credit: ESA/Rosetta

 

Comet 103P/Hartley (Hartley 2). Discovered in 1986, this comet is peanut shaped and its nucleus is approximately 1.5 km from end to end.

Image Credit: NASA/JPL/CalTech

 

1P/Halley. Comet Halley is probably the most famous comet because it was the first object to be recognised as a repeating visitor to our night skies. It is a larger comet and has a diameter of approximately 11 km.  In this image, you can see the cloudy tail behind the main rocky nucleus. Halley swings by every 76 Earth years and will be next seen in 2061!

Image Credit: ESA

 

Activity: View Comet ATLAS with the Liverpool Telescope 
The Liverpool Telescope has been observing Comet ATLAS since 1st April and will continue to do so as the comet approaches the Sun. You can use the telescope data to view the comet yourself. 

Activity: Comet on a stick

Things you will need:

  • A stick - maybe from the garden or a drinking straw
  • Sticky tape
  • A ball - you could try scrunching paper into a ball
  • Craft materials - a few of these: ribbon, strips of paper, fabric, cotton balls, tin foil, bubble wrap cling film, tissue paper etc
  • Hairdryer

No two comets are the same. They differ in size, shape and what they are made from. Don't worry if yours looks different, they are all different! 

Instructions What it represents
Find a stick. The stick is just for holding your model, it is not part of the comet. 
Attach a ball to the stick. Scrunched up paper would work well. The main ball is the comet nucleus. It is like a dirty snowball made of ice and rock.
Add some smaller balls to your main ball. You could use bits of cotton wool. As the comet gets closer to the Sun, the surface of the comet nucleus warms up and ice starts to melt off along with other rocky debris. 
Wrap your bumpy comet in cling film, bubble wrap or foil. The icy and rocky particles make a cloud around the nucleus called a coma. The Sun makes the coma light up.
Use ribbons or streams of material to create a 'tail'. Let them drop down naturally (don't try and force them to trail) The sunlight also pushes the material into the brightly lit tail of the comet.
Use a blue ribbon or pipe cleaner and stick it to the end of the comet at a slightly different angle to the main tail This is the ion tail of electrically charged gas (plasma).

Well done, you've made your model comet! Now let's simulate what happens as it orbits the Sun. 

Comet demonstration with the Sun (hairdryer)

For this you'll need x2 people and a hairdryer.

  • The first person holds the hairdryer and points it at the comet at all times. The hairdryer is the Sun and should be inside the comet's orbit.
  • The second person holds the comet by the stick. They should move in a highly elliptical orbit (like a squashed circle or oval) around the Sun (the person holding the hairdryer). The diagram below shows the shape of the orbit of the comet. 
  • As the comet gets closer to the Sun, the debris of the comet is pushed away by the wind from the hairdryer.
  • As your comet travels far away from the Sun, the tail of the comet will drop - this shows the Sun has less of an effect on comet when the comet is further away. 

Why do comets have two tails? 

Most comets have two tails. The tails appear as the comet approaches the Sun. Energy and particles from the Sun (solar wind) push on the comet and create a tail of gas and dust behind the comet. The gas tail is made of electronically charged molecules of gas (called ions) and points directly away from the Sun. However, the rocky tail is slightly curved towards the orbit. The gas and dust have different weights and so they separate which is why two tails appear. 

 

WARNINGS

  • Don't run with your stick
  • Put some tape or something similar over the end of the stick if it sharp
  • Careful not to trip over the hairdryer wire
  • Keep the hairdryer on a low heat temperature, beware of burning