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The Night Sky from Beaumes de Venise: 1 Summer

Updated: Mar 26


These are some amateur thoughts about what can be seen in the night sky in summer from Beaumes de Venise in the south of France. I have written it mainly for children, specifically my grandchildren, who might enjoy looking for the stars when they visit and when they are allowed to stay up late enough. But a friend has said that maybe some adults might find it interesting, particularly those living in northerly urban areas where we don't see the stars much. They may even find in it things they don't know - even if they do know about the Moon and the Milky Way. I will expand it come winter, to deal with the things that can be seen later in the year.

Milky Way

Maybe it’s best to start with the Milky Way, even though it’s normally pretty difficult to see.

As most people probably know, it’s really what we can see from Earth looking into the centre of our galaxy. This means that, although it looks like a milky cloud spread across the sky, it’s really billions of stars that are too far away to be seen individually.

In fact, everything we can see in the night sky (with at least one major exception, which we’ll come to) is within our galaxy. Our galaxy, known as the Milky Way galaxy (the word "galaxy" comes from the Greek for milk). consists of billions of stars of which the Sun is just one. The galaxy is spiral in shape, rather like a huge catherine wheel lying on its side. Our sun is on one of its limbs, certainly not at the centre but also not right at the edge.

Summer Triangle

In order to see the Milky Way, we need some directions and in summer these are best provided by looking for the Summer Triangle, three of the brightest stars in the sky during July and August.

The Summer Triangle consists of Deneb, Vega and Altair. Looking towards the south, Vega is pretty much overhead. Deneb is down to the left. Altair is way down to the right. They form an isosceles triangle, two of its sides being roughly the same length, namely the two sides going down to Altair.

The Summer Triangle isn’t itself a constellation. Deneb is in the constellation of Cygnus (the Swan); Vega in Lyra (the Lyre); and Altair in Aquila (the Eagle).

Constellations are what appear to us to be groups of stars, which our remote ancestors thought they could see as shapes, mainly of animals and birds, and so named them accordingly. Interestingly, they are only groups of stars when seen from Earth. They are normally by no means groups. The stars in the groups are normally very far apart from each other.

Deneb

Let’s start by looking at Deneb, partly because it’s one of the most amazing stars in the sky and partly because its the best way to find the Milky Way.

Deneb is the Arabic word for tail, indicating how the Arabs were originally ahead of us in observing the stars - the names of stars are often Arabic. They thought of Deneb as being the tail of the swan.

Deneb is one of the most luminous stars known - it is 60,000 times brighter than the Sun. The reason that it doesn’t seem brighter than the other stars in the Summer Triangle is that it’s much further away. It is 1600 light years away - a light year being a measurement of distance, namely the distance light (at the speed of 86,000 miles a second) goes in one year. This means that the light we see coming from Deneb started coming here 1600 years ago, ie about 500 years before the Norman Conquest, not that long after the fall of the Roman Empire. All very hard to contemplate!

As I said, Deneb is also useful for finding the Milky Way. To the right of Deneb there are three much fainter stars in a line. They are the wings of the swan. If you then follow a line down towards Altair, there are more, fainter stars, representing (in the imagination of our

ancestors) the neck of the swan as it flies down towards Altair. This is essentially the line of the Milky Way.

The Milky Way is normally quite difficult to make out. It looks like a very faint cloud stretching across the sky. The best way to see it is to look in the right general direction and then, curiously, turn your gaze slightly away. For some reason, that often brings it into focus.

Vega

Vega is actually the brightest of the three stars of the Summer Triangle. It is only 27 light years away. So the light from it started its journey a few years before the Millenium. As it is

relatively closer, it appears to us to be brighter than Deneb even though actually Deneb is very much larger and more luminous.

Altair

Altair is the third star of the Summer Triangle and is much the same distance away as Vega, in its case 16 light years.

The Ecliptic

The Ecliptic is the name given to the plane in which the Earth goes around the Sun, but from our point of view it is the route the Sun takes as it seems to go across the sky. It is also, broadly, the same route that the Moon takes, and also the planets. This is because the Earth and the other planets go round the Sun on roughly the same plane. Simlarly, the Moon round the Earth. This means that, during the night, we can always see the Moon (if it is visible) and the main planets (when they are visible) in the part of the sky, looking towards the south, that goes from east to west - from Caromb to Beaumes de Venise in local terms! This is the Ecliptic. If you see what appears to be an unusually bright star on the Ecliptic, it is probably a planet, not a star. If you see a bright star in another part of the sky, ie towards the north, it is definitely not a planet and must be a star.

The Moon

As we all know, the Moon is the closest body to the Earth, going round the Earth roughly once a month - hence the word “month” of course.

The Moon is most impressive when it is “full”, ie when it appears as a bright perfectly shaped ball in the sky - always on the Ecliptic. This happens when the Sun, the Earth and the Moon are in a straight line. Or at least in almost a straight line. If they are completely in a straight line, you get an eclipse of the Moon, because the Earth is right in the way of the light going from the Sun to light up the Moon.

Each night after a full moon, some light disappears from its right side. Roughly seven nights later, it is half light and half dark, a so-called half moon. Roughly seven days after that, we can’t see the moon at all. This is because, although of course it is still going round the Earth, it is no longer in the sky at night. Actually, it is up there during the day but we can’t see it because of all the blue sky and sunlight. A few nights after it disappears, it reappears in the evening sky towards the west as a tiny crescent. This is the so-called new moon. After about 14 nights, it is a full moon again. These are the phases of the Moon.

We can easily see the Moon in close up with our telescope. This is definitely impressive: best when the moon is not full, enabling you to see the craters and hills better.

Planets

We can only normally see four of the planets. These are Venus, Mars, Jupiter and Saturn. (We should be able to see Mercury, but I have never tried.) The gas giants, Uranus and Neptune are not visible by amateurs like us; they were only discovered relatively recently (1781 and 1846 respectively) and were unknown to our ancient ancestors.

The interesting ones are Jupiter and Saturn. Jupiter because of its moons, Saturn, of course, because of its rings.

With our telescope, you can see the four moons of Jupiter that Galileo first discovered in 1610 with his 17th century telescope, known as the Galilean moons: Io, Europa, Ganymede and Callisto. There are now thought to be at least 95 moons around Jupiter.

Saturn requires an exercise of imagination. The rings appear not, frankly, as rings; they make the planet seem eliptical.

Distances

A word about the various distances.

The Moon is easy. We can understand it in miles. It is roughly 230,000 miles (380,000 km) away from the Earth.

The planets are still intelligible (just!) in miles. Jupiter is very roughly 500 million miles away; Saturn a billion miles.

But with the stars, we have to move into light years. One light year is about 6 trillion miles or almost 10 trillion kilometres. Calculating in miles or kilometres is hopeless.

The Milky Way is about 100 thousand light years wide. This makes Deneb (at 1600 light years) seem pretty close. And makes you understand why the Milky Way, as seen in our sky, seems vague and unclear.

Outside the Milky Way galaxy, you get into millions of light years. The nearest galaxy that we can just see with the naked eye is the Andromeda Galaxy, which is 2.5 million light years away. The light started on its journey to us before there were any human beings to see it. We will get onto that when we look at the night sky later in the year - which is different. I’ll try to describe that later on.

Looking north

The most obvious reason for looking north is to see the best known constellation of all - the Big Dipper.

The Big Dipper has many names, formal and informal. It’s really called Ursa Major or, in

English, the Great Bear. But it doesn’t look remotely like a bear, so people normally call it something else, like the Plough or the Saucepan (which it certainly does look like) or indeed the Big Dipper (not sure the reason for that).

One of the key points about it is that it helps you to locate the Pole Star. The stars all revolve around the sky as the year goes by. This is the reason that the sky in winter is different from the sky in summer, with largely different constellations. But the Pole Star is the one big exception. It is always up there. And it is always due north - or almost due north, if you want to be very precise. Very useful for navigators. All the other stars revolve round it. (Of course it’s really we who are doing the revolving, around the Sun. They stay where they are.)

To find the Pole Star, you take the two stars that are the right hand side of the pan (known as “the pointers”) and draw a straight line from them upwards. This should get you to the Pole Star. Looking from our house, the Pole Star is above the hill called the Graveyron that gives its name to the neighbouring village, St Hippolyte le Graveyron. It is also, of course, due north.

Shooting stars

The beginning of August is a good time for looking for shooting stars. Shooting stars are not stars at all. They are bits of debris that cascade into our atmosphere and (hopefully) burn up. This makes them look like stars careering across the sky.

The first few weeks of August is a good time to see some because of the so-called Perseid shower. The Perseids are meteors that have come off a comet - so I understand. People tell you that on the right night you can see as many as 60 during the night. Best of luck! Apparently, the best way of seeing them is to camp on the top of Mont Ventoux.

Sky in Autumn and Winter

See the next instalments.

Tony Herbert

16 August 2023

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