5 Largest Star Constellations in the Sky

Ursa Major
Image Credit: Niclas Lundin

Even professional astronomers sometimes admit to having difficulty recognizing all of the 88 modern constellations, as most constellations are marked out by some stars that are not that visible to the naked eye, except under exceptionally good seeing conditions. Regardless of the difficulties, recognizing star constellations can fill one with a sense of both satisfaction and humbling awe.

So to help you on your way, here is a list of the five biggest constellations in the night sky, as well as some of their main Messier and deep-sky objects (nebulae, star clusters, and galaxies). Why not go out tonight and see how many of them you can find?

1) Hydra

Hydra, (“Water Snake”) takes up 3.158% (1303 square degrees) of the night sky, making it the largest star constellation. This southern hemisphere constellation can be seen from between +54° and -83° of latitude, although best seen in April. Its head is located just to the south of Cancer, with the rest of its long, twisting body stretching all the way to a point between Centaurus and Libra, where its tail terminates.

Hydra contains around 238 stars but consists primarily of an asterism of 17 stars, the brightest of which is Alphard, an orange giant of magnitude +2 located 177 light-years distant. In Greek mythology, Hydra is associated with the Lernaean Hydra from the Twelve Labours of Heracles.

Deep Sky Objects in Hydra

Hydra contains three main Messier objects, namely M68 (globular cluster), M83 (Southern Pinwheel Galaxy), and M48 (open cluster). Other objects of interest include Tombaugh’s Globular Cluster (NGC 5694), and a planetary nebula called the Ghost of Jupiter (NGC 3242).

2) Virgo

5 Largest Star Constellations in the SkyVirgo (“Virgin”), is the largest constellation of the zodiac and takes up 3.138% (1294 square degrees) of the southern sky. It can be observed from latitudes between +80° and -80°, although best seen in May. Virgo also currently contains the autumn equinox point, where the Sun’s ecliptic crosses the celestial equator on Sept 23rd, marking the start of autumn in the Northern Hemisphere, and the beginning of spring in the Southern Hemisphere.

The constellation contains around 169 stars, of which only the blue-white giant Spica (+1.04) is of first magnitude. In mythology, the constellation Virgo represents Persephone, Queen of the Underworld, and the daughter of Demeter, the harvest and fertility goddess.

Deep Sky Objects in Virgo

Virgo contains the galaxies Messier 49, Messier 58, Messier 59, Messier 60, and Messier 87, as well as the Sombrero Galaxy (M104), the Eyes Galaxies, the Siamese Twins, and the quasar 3C 273.

3) Ursa Major

Ursa Major (“Big Bear”) takes up 3.102% (1280 square degrees) of the northern celestial sky, and can be seen between latitudes of +90° and -30°. It is one of the most recognizable constellations in the sky, with its seven most luminous stars forming an asterism known as the Big Dipper, although the constellation itself actually contains around 209 stars, the brightest of which is Alioth, a blue-white subdwarf of magnitude +1.76 situated 81 light-years from Earth.

As well as containing one of the most recognizable asterisms, together with Orion and the Southern Cross, Ursa Major is also one of the oldest constellations known to the ancients and features prominently in all major cultures and mythologies.

Deep Sky Objects in Ursa Major

Ursa Major contains a number of notable galaxies, such as the Pinwheel Galaxy (M101), Bode’s Galaxy (M81), and the Cigar Galaxy (M82), while the planetary Owl Nebula (M97) is also situated in Ursa Major, 1,630 light-years away.

4) Cetus

Cetus (“The Whale”) takes up 2.985% (1231 square degrees) of the northern sky, and is visible from latitudes between +70° and -90°, although best seen in November. It is located in a celestial region known as “The Water”, together with other constellations whose names also evoke aquatic images, such as Aquarius (water bearer), Pisces (the fish), and Eridanus (the river).

In mythology, Cetus is associated with princess Andromeda, who was due to be sacrificed to a sea monster in retribution for her mother, Queen Cassiopeia, offending the sea-god Poseidon with her boastful claims. Fortunately, she was saved by Perseus, who swooped in on the winged horse Pegasus just in time. Cetus was also one of the constellations first cataloged by Ptolemy in the early 2nd century.

Brightest amongst Cetus’ 189 or so stars is Deneb Kaitos (Beta Ceti), an orange giant with an apparent magnitude of +2.02 found 96.3 light-years distant. Other stars of note include Menkar (Alpha Ceti), Tau Ceti, and the variable star Mira (Omicron Ceti), all of which are well-known for various reasons.

Deep Sky Objects in Cetus

Amongst the notable deep sky objects in Cetus is Messier 77, a barred spiral galaxy 50 million light-years from Earth, and the planetary nebula NGC 246, also known as the Cetus Ring or “Pac-Man Nebula” because like the video game character, it seems to be chomping down on its surrounding star field.

5) Hercules

Hercules takes up 2.97% (1225 square degrees) of the northern sky, and can be viewed from latitudes between +90° and -50°, although best seen in July. The constellation contains around 245 stars, none of which are particularly luminous, including its brightest star Kornephoros (Beta Herculis), a yellow star found 139 light years distant of magnitude +2.81.

Its other notable stars include the red giant Ras Algethi (Alpha Herculis), a third to fourth-magnitude star which marks the head of Hercules, as well as four stars known as the Keystone asterism, which represent the legendary hero’s chest as he stands over the slain dragon, Draco.

In mythology, the constellation Hercules is most often associated with Heracles’ Twelve Labors, of which the penultimate was the stealing of Hera’s golden apples which were guarded by the dragon Ladone in the Garden of the Hesperides. The legendary strongman ended up slaying the luckless dragon, which has since been associated with the constellation Draco.

Deep Sky Objects in Hercules

Hercules is home to the brightest globular cluster in the northern hemisphere, namely the Great Globular Cluster (M13), which is 25,200 light-years away and contains over 300,000 stars. M92 is another bright globular cluster in this constellation, and holds the distinction of being the oldest yet discovered at 14 billion years old.

The planetary nebulae Abell 39 and NGC 6210 can be found in Hercules, as well as the Hercules Cluster (Abell 2151) of galaxies, and the galaxy cluster Abell 2199. Last but not least, the night sky’s 5th largest constellation contains the largest known superstructure in the universe, the Hercules–Corona Borealis Great Wall, which is a massive group of galaxies 7.2 billion light-years across, 10 billion light-years long, and around 1 billion light-years in depth.

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