The Weekly Facts to learn this week are –
a) Stars – Learn one star constellation and how to find it.
b) Clouds – learn one cloud formation, what it looks like and what it means for weather prediction.
Constellations are arbitrary groupings of stars that are used to tell different ones apart. Scientists recognise 88 of them (since 1922). The star gazer or astronomer needs to know these constellations and their locations because it then allows them to find other objects in the sky e.g. planets.
People have been using the stars for thousands of years. Sailors have used them to help with navigation. It has also helped our ancestors to mark the passage of time because they can be used to mark seasons (as most constellations only appear in certain seasons). This has allowed farmers to use them to know when to start planting and when to harvest.
The names of Constellations have come from early European history or from Greek myths. In the Greek stories, those heroes who couldn’t attain immortality at death were placed in the sky as stars. Some constellations were also named after animals.
The sky appearance changes over time because the earth spins and moves. However, there are five constellations that can always be seen above the horizon in the northern hemisphere – Ursa Major, Ursa Minor, Cassiopeia, Cepheus and Draco. They all revolve once in 24 hours around the North Star and so they are known as Circumpolar Stars. This year I wish to focus firstly on these five constellations as well as some other well known ones like Andromeda, Orion, Bootes and Pegasus. In 2014 I hope to go through each of the Zodiac constellations.
So, why should we be astronomers? As earth-centic people, we often forget that there is a big, vast universe out there, and it is all part of nature too. It is as equally worthy of reverence and respect as any other part of nature. The stars and space have an ability to inspire awe and reverence in us in a way nothing on earth can. Looking up at the night sky on a clear dark night will reveal the vastness of the immense universe and invoke a humility we rarely experience at other times. By learning the names of the constellations we can connect with our past – learning the ancient myths and stories of our ancestors. We can recognise the seasons. We are able to connect on a deeper level with the universe than just looking up and seeing the night sky. Did you know that there is actually another galaxy that can be seen in the night sky with the naked eye? Amazing!!!
Also known as the Great Bear, Ursa Major is one of the most well known constellations and can be found in the sky of the northern hemisphere throughout the year. It also contains the set of stars named the Big Dipper or Plough which look like a saucepan…however these are only part of it. The stars Merak and Dubhe are known as the “pointer stars” because they point in a line to the North Star, Polaris which allows us to find true north.
The Greek myth behind this Constellation is that Zeus, the king of the Gods, lusted after a young women named Callisto. In revenge, Hera, Zeus’ jealous wife, transforms Callisto into a bear. Callisto later encounters her son Arcas who shoots the bear, and so Zeus turns Arcas into a bear too and puts them both in the sky – Ursa Major and Ursa Minor. The constellation was also known as “Helike” meaning “turning” in ancient times, because it turns around the pole.
To find Ursa Major, look for the large saucepan like constellation of seven stars. That forms the back and tail of the Bear, next to the bowl of the saucepan is an almost arrow shape forming the head and below the bowl of the saucepan are the legs (see below). Over this next week, go out and see if you can find it.
Clouds are tiny drops of water or ice crystals (depending on the temperature) that have settled on dust particles in the atmosphere. There is water all around us in the form of tiny gas particles known as water vapour. When the air is saturated and cannot hold any more water vapour (e.g. due to evaporation), the water vapour condenses into visible water droplets or ice crystals and these form clouds.
Clouds are classified into ten main groups based on whether they are high level clouds (occur above 20,000ft), medium level cloud (occur 6,500 to 20,000ft) or low level clouds (occur below 6,500ft). High level clouds are Cirrus, Cirro-Stratus and Cirro-Cumulus. Medium level clouds are Alto-Stratus, Alto-Cumulus and Nimbo-Stratus. Low level clouds are Stratus, Cumulus, Cumulo-Nimbus and Strato-Cumulus. Over the coming months, I will explore each of these ten.
To make it easier to remember, it’s good to know what some of the language means. Clouds with the name ‘Cumulus’ are in a heap, puffy or in a pile. Clouds with the name ‘Stratus’ are layered, long & streaky. Clouds with the word ‘Nimbo’ will bring rain.
When watching clouds for weather prediction, it is important to remember that if clouds are becoming lower or if fluffy cumulus clouds begin to grow rapidly upwards, that is a sign of rain or a storm coming.
Cirrus clouds are short, thin, wispy and have a fibrous hair-like or silky appearance like tufts of hair. They are the highest clouds and are composed of ice crystals. They often look like delicate brush strokes and have a hooked appearance. They are usually whiter than any other cloud in that part of the sky and may sometimes take on the colour of sunrise or sunset.
They often point in the direction of air movement and while they mean there is fair weather now, a large number together are also a sign that something is happening which could be either good or bad e.g if they are moving fast, it is a sign of a change in weather conditions over the next 24 hours.