Comets and Shooting Stars

Comets have been observed and recorded by many cultures since ancient times. They have often been interpreted as harbingers of doom. In the past they were thought to foretell of events as diverse as earthquakes, floods, hail storms, heat waves, poor harvests, epidemics, war and high prices!

Comets were said to foretell disasters
Comets were said to foretell disasters

But by 1700 most scholars had concluded that these events happened whether there was a comet or not.

Visitors from deep space

Comets are cosmic snowballs of frozen gas, rock and dust that orbit the Sun.

They usually have highly eccentric elliptical orbits. The time they take to orbit the sun is very variable. Some take only a few years, whereas others may have orbits lasting as long as several million years. Short period comets originate in the Kuiper belt which lies beyond the orbit of Neptune. Long period comets are thought to originate in the Oort cloud which extends from outside the Kuiper belt to halfway to our nearest star!

Comet nuclei range from a few hundred metres to tens of kilometres across and are composed of loose collections of ice, dust, and small rocky particles. When comets get closer to the Sun they warm up and begin to release gas and dust. This produces a visible atmosphere or coma. A comet’s coma may be up to fifteen times the Earth’s diameter. Some comets can get bright enough to be seen from Earth without the aid of a telescope.

Comet Tails

As a comet approaches the sun, some of the gas and dust in the coma is blown away by solar radiation. This force exerted by the Sun is large enough to create an enormous “tail” from the dust and gas.

The streams of dust and gas form distinct tails, each pointing in slightly different directions. The dust is pushed out of the coma by radiation pressure. It then continues to follow the comet’s orbit around the sun often forming a curved tail. On the other hand the gas in the coma is ionised by the solar radiation. Because these charged particles are more strongly affected by the solar wind they form a separate tail that always points directly away from the Sun. Comet tails can stretch as far as the distance from the Sun to the Earth.

Comet Wirtanen passing the Pleiades on December 17th 2018
Comet Wirtanen passing the Pleiades on December 17th 2018
Comet 46P / Wirtanen

Comet 46P/Wirtanen is a short-period comet with an orbital period of 5.4 years. It is relatively small in size, with an estimated diameter of just 1.2 kilometers.

However this one came really close.

On December 16th it passed by at a distance of only 7 million miles from Earth. By then it was neatly positioned between the Pleiades and Hyades star clusters – a really favourable place for us to see it high in the sky after sunset.

This icy space rock was luminous enough to be just visible with the naked eye. It was the brightest comet that we are likely to encounter for at least another five years.

We hope you didn’t miss it!

Meteor Showers

Meteor showers are caused when the Earth passes through the trail of debris left by a passing comet. This debris is moving at extremely high speeds and usually burns up on entering the atmosphere to create shooting stars. Most meteors are smaller than a grain of sand, so almost all of them disintegrate and never hit the Earth’s surface.

Because meteor shower particles are all travelling on parallel paths, and at the same speed, they appear to come from a single point in the sky. That point is called the radiant. Meteor showers are almost always named after the constellation in which the radiant is situated.

A shooting star
A shooting star

Tomnavoulin gets New Lights

Full cut off street lighting in Tomnavoulin
Full cut off street lighting in Tomnavoulin

Moray Council have just finished installing replacement street lighting in Tomnavoulin with “full cut off” LED units. A great improvement because as you can see they only illuminate downwards where we need the light. Also good for our wildife, reducing our carbon footprint and the cost of running the lighting. It all helps to keep our council taxes down in future.

Dark Sky Discovery Sites

Brand new interpretation boards were installed at our three Dark Sky Discovery sites last week: The Field of Hope, The Carrachs and Blairfindy Moor. They have got information to get you started on your star gazing adventures. But you will need to visit all three to get the whole story.

The Field of Hope - Tomintoul's Dark Sky Discovery Site
The Field of Hope – Tomintoul’s Dark Sky Discovery Site

Here’s where to find them:

Dark Sky Discovery Map
Dark Sky Discovery Site Map

The Queen and Pegasus

Cassiopeia

To find Cassiopeia first find the Plough. Then draw an imaginary line through the Pole Star from the star that joins the handle of the Plough to it’s body. That will take you to the big “W” of Cassiopeia.

Cassiopeia was the wife of Cepheus, King of Ethiopia, and mother of princess Andromeda. She boasted that her daughter Andromeda was more beautiful than the Nereids. Poseidon, who was the Nereids father did not agree. So he sent a monster, Cetus, to terrorise the Ethiopian coast. When Cassiopeia and Cepheus consulted an oracle to find out how to get rid of the monster they were told to tie Andromeda to a rock for the monster’s dinner.

In a gross dereliction of parental responsibility Cassiopeia and Cepheus followed the oracle’s recommendation. However just in the nick of time along comes Perseus, rescues Andromeda and they all lived happily ever after… except for Cassiopeia and Cepheus: Zeus had them chained to their thrones and put them in the night sky to spin around the Pole Star for ever as punishment for their despicable behaviour.

Star Map of Cassiopeia & Pegasus
Star Map of Cassiopeia & Pegasus

Now get those binoculars out and check out these two star clusters in Cassiopeia:

Caroline’s Rose

NGC7789 is also known as “The White Rose” Cluster or “Caroline’s Rose” because when seen visually, the loops of stars and dark lanes look like the swirling pattern of rose petals as seen from above. It was discovered by Caroline Herschel in 1783.

Caroline's Rose
Caroline’s Rose

The Owl Cluster

NGC 457 is also known as the Owl Cluster or ET Cluster. It has two bright stars – the eyes of the Owl or ET, that can be seen staring back at you as you spy the cluster through your binoculars.

The Owl Cluster
The Owl Cluster

Pegasus

In Greek mythology Pegasus was a winged horse with magical powers. There are many stories told of his exploits: He helped Perseus slay the gorgon Medusa and Bellerophon to kill the Chimera. He was also the bearer of thunder and lighting for Zeus, the chief of the gods.

The constellation of Pegasus can be recognised from the “Square of Pegasus” – a large and conspicuous feature of the autumn night sky.

Messier 15 – A Globular Cluster

Right out on the western edge of Pegasus is M15 – a globular cluster. Globular star clusters are believed to be the remains of ancient galaxies cannibalised by the Milky Way. Some of them are almost as old as the universe itself.

Messier 15
Messier 15

Through binoculars M15 will appear as a small fuzzy ball of light. In reality it contains over 100,000 stars and is 12 billion years old. You can find it using the star map above.

Blood Moon

Blood Moon
Blood Moon

A blood moon was a dramatic event for early civilisations. Here are some tales from long ago:

Giant Wolves

According to Viking mythology the monstrous wolf Fenrir had two sons, Sköll and Hati. Sköll

would chase the Sun whilst Hati ran after the Moon. If either the Sun or Moon were caught then there was an eclipse.

During an eclipse the Vikings used to try and rescue the Sun or Moon by making as much noise as possible to scare off the giant wolves.

A Substitute King

The ancient Mesopotamians also saw lunar eclipses as an attack on the moon. But in their stories, the assailants were seven demons.

Now the Mesopotamians regarded an attack on the Moon as an assault on their king. But being fairly good at predicting eclipses they could make preparations in advance.

So during the attack they would install someone expendable as a substitute king whilst the real king pretended to be an ordinary citizen. Afterwards the substitute would quietly disappear, possibly by poisoning, and the real king would resume his duties.

A Jaguar

The south American Inca believed that during a lunar eclipse a jaguar attacked the moon and ate it. The feline assault explained why the moon turned blood red.

During lunar eclipses the Inca would shake their spears and beat their dogs. They hoped that this would make enough noise to frighten the big cat away and stop it eating anyone.

Twenty Wives

The Hupa tribe, also in the Americas, believed that the moon had twenty wives and many pets. Most of the pets were mountain lions and snakes. When the moon didn’t bring them enough food they attacked him until he bled. However before long the moon’s wives would come to his rescue and collect his blood to restore him to health. And so the eclipse would end.

What is really going on?

A “blood moon” occurs when the Moon is in total eclipse.

The Moon takes about 27 days to orbit the Earth. Roughly once per month the Moon is directly opposite the Sun. But because the Moon’s orbit is at a slightly different angle to the Earth’s orbit the Earth does not usually get in the way of the sun and we see a full Moon.

However sometimes the orbital plane of the moon lines up with the orbital plane of the Earth and the Earth blocks the sunlight from falling on the Moon. That is what causes a lunar eclipse.

When the sunlight is only partially blocked by the Earth we get a partial eclipse and the Moon darkens slightly. As the eclipse begins a dark shadow can be seen taking a bite out of the edge of the Moon. When the Moon moves directly behind the Earth then we get a total eclipse and the moon goes very dim. The colour turns red because a small amount of light still reaches the lunar surface, refracted through Earth’s atmosphere.

So the red colour of the Blood Moon is the light of every sunrise and sunset on Earth being simultaneously reflected back at us from our Moon.

Planners back Dark Skies

We were delighted to hear this week that planners will be backing our bid to become an International Dark Sky Park. Both the Cairngorms National Park Authority and the Moray Council have written to confirm that they will be using our Lighting Management Plan as a material consideration in determining planning applications within our proposed Dark Sky Park.

Planners back Dark Sky Park
Planners back Dark Sky Park

Lighting Amnesty

Our lighting amnesty got off to an excellent start on Saturday with an event in Tomintoul. We celebrated International Dark Skies week with an offer to replace local residents outdoor lights with dark sky friendly ones.

If anyone in the proposed Dark Sky Park area has an outdoor light that allows excessive light to spill into the surrounding countryside and night sky then a free replacement unit can be obtained from the Landscape Partnership office in Tomintoul.

Download our Lighting Amnesty Leaflet to find out more.

Dark Sky Friendly Lighting

The Lion and the Crab

Finding The Celestial Lion

To find Leo start at our old friend the Plough and follow the two pointer stars in the opposite direction from the Pole Star. Just under a quarter of the way across the sky look out for a group of stars shaped like a backwards question mark.

This is the Sickle – the head of Leo the Lion. The star at the bottom of the question mark is Regulus, his shining heart and one of the brightest stars in the night sky.

Starhop to Leo

Leo The Lion

In Greek mythology, Leo was said to be the Nemean Lion, killed by Hercules during the first of his twelve labours. The Nemean Lion would take young women as hostages to its lair in a cave. Warriors from a nearby town had all been eaten in their attempts to rescue them because the lion’s hide was proof against all known weapons. Hercules quickly realised that in order to defeat the Lion it was going to be a bare knuckle job. Slipping quietly into the cave Hercules engaged it at close quarters. As the Lion pounced he grabbed it in mid air, catching the Lion’s forelegs in one hand and it’s hind legs in the other. Bending it backwards he broke its back and freed the trapped maidens. Zeus, chief of the Greek gods commemorated his efforts by putting the Lion in the sky.

The Beehive (M44)

Move 25 degrees west from the centre of Leo (the distance between your outstretched thumb and little finger at arm’s length) and look for a fuzzy patch. This is the Beehive cluster in the constellation of Cancer the Crab.

The Beehive cluster looks like a nebulous patch of light to the naked eye under dark skies. Through binoculars it looks like a swarm of bees buzzing round a hive. It has been known since ancient times and is sometimes called Praesepe meaning “the manger” from Latin.

Also known as Messier 44, the Beehive is one of the nearest open clusters to the solar system. Even so the light that we see today started on it’s way here during the Wars of the Roses. The Beehive contains around a thousand stars – more than most other nearby clusters.

The Beehive Cluster
The Beehive Cluster (wiki commons)

The Crab

The Beehive cluster lies in the middle of the constellation of Cancer the Crab. Cancer is such a faint constellation that it could easily be missed if it were not for the Beehive cluster.

During Hercules’ epic battle with the multi headed Hydra, Hera sent Karkinos the crab to distract him. However quick witted Hercules swiftly dispatched the crab by kicking it with such force that it ended up in the sky. Hera gave Karkinos a permanent place in the starry heavens in gratitude for it’s efforts.