Before introducing the bright stars and constellations in summer, the Milky Way in summer is also one of the major wonder of the summer starry sky. Summer is the season most suitable for observing the Milky Way. Not only can we observe the brightest part of the centre of the Milky Way, but we can also observe the Milky Way in the night sky with the longest duration when compared with other seasons. Even in Hong Kong, which is well-lit all year round, when we go to the countryside, we shall be able to observe the splendid Milky Way provided that the weather is fine.

Photo taken at the Astropark in Sai Kung , Image Credit：Mew Chu

Summer Triangle

There are more bright stars in summer than in spring and they are brighter too. Perhaps you may not have heard of the Summer Triangle but you must have heard about the romantic legend of "the Cowherd and the Weaving Maid". Legend has it that the Cowherd and the Weaving Maid are permitted to meet each other only on the seventh evening of the seventh moon each year on the bridge formed by magpies across the Milky Way. In the summer night sky, you can find Altair and Vega on the east side and the west side of the Milky Way and they are the brightest stars in Aquila and Lyra respectively. Altair, Vega together with Deneb in Cygnus, which is located at the Milky Way form the Summer Triangle. As the pattern of Cygnus resembles a huge cross, it is also known as "the Northern Cross".

Heart of the Scorpion and the Teapot with Rising Steam

Near the centre of the Milky Way is a reddish bright star, Antares, the brightest main star of Scorpius. It is also known as "Huge Fire". Scorpius can be counted as the most recognizable constellation in the summer starry sky. It is made up of stars that form the English letter "J". The tail of "J" resembles the curving tail of a scorpion whereas the reddish Antares, located at the upper half of the body of the scorpion, seems like its "heart".

Apart from Scorpius, another constellation appearing in summer is the well-known Sagittarius. Several stars of it form the shape of a teapot. As it is located at the centre of the Milky Way, at a glance, the Milky Way seems like a puff of steam rising from the spout of the teapot.

Autumn is the season that has the least number of bright stars. Yet the roles and backgrounds of those stars that appear are well-known in ancient mythology. Members of "the constellations of the Royal Family" include Cepheus, Cassiopeia, Andromeda and Perseus. With the autumn night sky as the background, Cepheus is like a knight on a winged horse (Pegasus), rescuing the princess from the sea monster (Cetus). He succeeded in doing so and married the princess as well, weaving a fairy tale of "a hero saving a damsel in distress".

Besides, Andromeda is also where we can find a large galaxy nearest to us. Moreover, one of the stars of Cepheus is the first variable star (Cepheid variable) discovered by astronomers and its luminosity varies periodically. Algol, also known as the "Demon Star", is a bright star in Perseus. Thanks to "the constellations of the Royal Family", the sombre starry sky in autumn becomes worthy of observation and study.

Making use of Cassiopeia to find the North Pole

For places with a low latitude such as Hong Kong, sometimes the tail of Ursa Major will be below the horizon. Hence, we have to make use of another more recognizable constellation, Cassiopeia, to locate Polaris. The stars that form Cassiopeia appear like the English letter "W". Extend the lines on the left and right of "W" until they intersect. By linking the intersection point with the star in the middle of "W" and extending the distance by 5 times, there you find the whereabouts of Polaris.

Andromeda Galaxy, which seems to be near to us and yet so far away

Andromeda Galaxy, a large galaxy which is closest to our Milky Way, is designated M31 in the Messier Catalogue*. Hence, it is generally known as M31 Andromeda Galaxy. Despite being the nearest galaxy to us, it is still 2.5 million light years away from the Earth (i.e. approximately 23,651,826,181,450,100,000 km!). Astronomers estimate that M31 Andromeda Galaxy has a diameter of 200,000 light years. Owing to its huge size, under fine weather conditions in autumn and winter, it is faintly visible by the naked eye. Although it looks like a hazy patch, it is already one of the farthest deep-sky objects that is visible to the naked eye.

*Messier was a French astronomer who compiled a catalogue of 110 astronomical objects, including nebulae, star clusters and galaxies during the period from 17th C to early 18th C. The catalogue came to be known as the Messier Catalogue.

In spring and summer, we can observe the astronomical phenomenon of the "Triangle" whereas in autumn, we can observe the "Autumn Square", which consists of 3 bright stars of Pegasus and 1 bright star of Andromeda. In the autumn starry sky, there is also a bright star "Fomalhaut" of Piscis Austrinus which appears in the south. The Hubble Space Telescope has captured images of "Fomalhaut b", a planet of "Fomalhaut". It is the first exoplanet that can be observed by visible light directly. Other constellations that can be observed in the autumn night sky include Aquarius, Pisces and Capricornus.

Finally comes the starry sky in winter, which of course will not disappoint us. The starry sky in winter has the largest number of bright stars, each of them being so dazzling. Full of bright stars, star clusters and nebulae, the starry sky in winter becomes all the more brilliant.

Orion, King of Constellations

The most instantly recognisable constellation in the starry sky of the four seasons must be Orion. It is also known as "the king of constellations" and "the Winter Constellation". With its luminous stars, even amateurs can easily identify it. The brightest star is the bluish-white Rigel, and the second brightest star is Betelgeuse which is a red supergiant star.Three stars form a horizontal line representing the belt of Orion. Below the belt is one of the most famous deep sky objects, M42 Orion Nebula.

Notorious Sirius

Sirius, the brightest star of Canis Major, is also the brightest star in the entire night sky. It is only about 8.6 light years from the Earth. In ancient times, quite a number of countries considered it an ominous star. In ancient Egypt, people thought that the rising of Sirius before the sunrise signify the imminent flooding of the Nile whereas ancient Greeks considered intense twinkling of Sirius as a sign that something bad would happen.

The Zeus turned Taurus

In mythology, Zeus, the King of Gods turned himself into Taurus. In the starry sky, Taurus seems to be blessed by the Heavenly God to have many bright stars, of which the most luminous one is Aldebaran (Taurusα), orange red in colour, with an apparent magnitude of 0.86, representing the eye of the "bull". The Hyades is a loose star cluster which is located at the face of the "bull". It is also the nearest star cluster to us. M45 The Pleiades, also known as The Seven Sisters, is a very luminous star cluster. Not only can it be easily seen by the naked eye, but it also form the shape of a question mark when observed through binoculars.

Winter Triangle and Winter Circle

The Winter Triangle, found in the Winter Circle, is an almost equilateral triangle composed of Sirius in Canis Major, Procyon in Canis Minor and Betelgeuse in Orion. As the three stars are nearly of the same brightness, they can be easily recognised in the night sky. After finding the Winter Triangle, look further and you can see the Winter Circle. The Winter Circle, also known as the Winter Hexagon, is made up of Rigel in Orion, Sirius in Canis Major, Procyon in Canis Minor, Pollux in Gemini, Capella in Auriga and Aldebaran in Taurus. You can spot this hexagon even in a brilliantly illuminated city. Next time, gaze at the sky in winter and you will have amazing discovery.