Cassiopeia

Stargazing on a clear night is an enjoyable experience.

With a bit of starlore and knowledge, the experience becomes more intense.

In this blog, we’ll focus on one particular constellation.

Our Constellation Close-Up is Cassiopeia.

Cassiopeia is a distinctive star pattern.

It is almost overhead in our autumn night sky.

So now is a good time to learn more about the mythical Queen.

And it’s a chance to feature my all-time favourite star cluster.

Constellations

The astronomer’s sky is divided into 88 areas.

These areas are the constellations, star patterns.

Our constellations are based mainly on the ancient Greek patterns.

All our star maps come courtesy of Stellarium.

Stellarium is a superb planetarium programme.

It shows the sky on any date and at any location.

You can download stellarium free, click here.

Cassiopeia mythology

In Greek mythology, Cassiopeia was queen of Aethiopia.

Her star pattern was one of the 48 original Greek constellations.

The queen boasted of her beauty and in doing so, annoyed the sea-god Nereid.

Nereid obviously had a low threshold of anger.

He rather over-reacted and sent a sea monster to terrify Cassopiea’s people.

The queen had to offer her daughter, Andromeda, as a sacrifice to send the monster away.

Only the intervention of Perseus and his flying horse Pegasus saved the princess.

All the character in this drame are represented by constellations in the autumn night sky.

So let’s look where the story began.

Let’s take our astronomical close up look at Cassiopiea.

The ‘W’

The five brightest stars of Cassiopiea make a distinctive letter ‘W’ shape.

This makes it one of the easiest constellations to recognise.

And it’s overhead in the darkest part of the night sky through autumn.

Let’s look at the five main stars in detail, moving from left to right of the ‘W’.

Top left of the ‘W’ is Epsilon Cas.

It’s about 410 light years away and is a hot blue-white star.

Epsilon Cas is four times wider than our Sun and spins much more quickly.

Next, the first dip in the ‘W’, is delta Cas, known as Rukbat.

Rukbat, ‘the knee’, is around 100 light years away.

The light we see left the star in 1924.

The middle star is gamma Cas.

It’s light varies unpredictably and it probably has an unseen companion star.

This central star is 550 lightyears away, the most distant in the ‘W’.

The light from this huge star set off at about the same time that Nicolaus Copernicus was born.

We dip down again to alpha Cas, Schedar,  the brightest star in the constellation.

This is an orange-red giant, almost 800 times wider than the Sun.

Schedar is around 230 light years away.

Up to star five, the final line in the ‘W’.

This is beta Cas, the second brightest star, also known as Caph.

Caph is a white star rotating quickly, in just over a day.

It spins itself into an oblate spheroid, a somewhat squashed ball of gas.

Beta Cas shines 20 times brighter than the Sun and is 55 light years away.

As you can see, these five stars are at very different distances.

They have no connection with each other.

It is only from our vantage point that they form a letter ‘W’.

Deep Sky objects in Cassiopeia

The Milky Way runs through Cassiopiea.

It is well worth scanning the constellation with binoculars to appreciate the starry richness of our galaxy.

Cassiopiea also contains several star clusters.

My favourite is NGC 457, the Owl Cluster.

NGC 457, Owl Cluster

A telescope is needed to see this celestial bird.

In the image, the owl’s bright eyes are at top left.

His body spreads down to the right with his wings outstretched.

His feet are two more stars at bottom right.

He’s also known as the ET cluster, after the eponymous movie.

There are over 100 stars in the cluster.

However the brightest, the owl’s right eye, phi Cassiopeia, may not be one of them.

The cluster is around 7,900 light years away.

If you see this lovely collection of stars, you have a connection with a celebrity astronomer of the past.

NGC 457 was discovered by William Herschel on August 18, 1780.

He used a 6-inch reflector, quite a small telescope.

So if you have a telescope, no matter how modest, you might find the celestial owl.

The author: Dennis Ashton is a Fellow of the Royal Astronomical Society and a Wonderdome presenter.

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