Sirius is in the 'southern celestial hemisphere'; i.e. it's south of the ecliptic (the plane in which the planets orbit the Sun), and from the Earth's northern hemisphere it's only visible in winter. It can however be seen at times from any latitude below 73 degrees north (some distance north of the Arctic Circle, which is at just a tad over 66.5 degrees north).
In the UK (and the USA), Sirius can be observed throughout the winter and until about mid–April. It rises in the south–east, arcs across the southern sky, and sets in the south–west. In December it rises in mid–evening; by mid–April, Sirius is setting in the southwest in mid–evening.
Sirius is not as bright as Jupiter or Venus; but it is brighter than Saturn, and at times it's brighter than Mars or Mercury.
To find Sirius: find Orion's belt, and follow an imaginary line drawn through it and extended to your left. Sirius is about eight times as far from the belt as the belt is wide (and actually slightly below this line).
Sirius forms one vertex of what astronomers know as the Winter Triangle. The other two stars that make up the triangle are Betelgeuse (Orion's left shoulder) and Procyon, which is the brightest star in the constellation Canis Minor. Procyon is to Orion's left, about the same distance from Betelgeuse as Sirius. In fact the Winter Triangle is almost perfectly equilateral – the three stars are all at about the same distance from each other.
Sirius, Betelgeuse and Procyon are the three brightest stars visible in the winter sky from the northern hemisphere.
Sirius is the brightest star that's visible from anywhere on the Earth's surface. It's nearly twice as bright as Canopus, the second brightest, which is never visible from north of about 37 degrees North (roughly the latitude of Lisbon, Athens, northern Afghanistan, the northern edge of the Tibetan plateau, Seoul, San Francisco, and Richmond, Virginia).
The third brightest star is Rigil Kent, in the constellation Centaurus (the Centaur) – also known as Alpha Centauri, and not to be confused with Proxima Centauri, which is the nearest star to the Sun. Proxima Centuri is actually part of the same star system as Alpha Centauri, but it's too faint to be seen with the naked eye. (It's a red dwarf, with a diameter approximately one–seventh that of the Sun. About fifty of the sixty stars that are nearest to the Sun are red dwarfs.)
Centaurus is south of the ecliptic, and the northernmost latitude from which the Alpha Centauri star system can ever be seen is 27 degrees north (just south of the Canary Islands and Cairo, Bahrain, Delhi, south to central China, northern Mexico, or mid–Florida).
The fourth brightest star, and the brightest of all those that are north of the ecliptic, is Arcturus, in the constellation Boötes (the Herdsman). To find it: find the Plough (or Big Dipper), and follow a line drawn through the two stars that form the bottom of the 'saucepan' in a clockwise direction (the same direction as the hande of the 'saucepan'). The distance to Arcturus is about five times the distance between the two stars in the Plough.
© Haydn Thompson 2017