Hydra (Pronounciation:Hi-dra, Abbrev:Hya, Latin:Hydrae) is a constellation, one of 88 constellations that the night sky is divided into. The sky is not divided up equally between the constellations. Hydra takes up 1302.844 sq. degrees of the night sky which equates to 3.16% of the night sky. Hydra is the 1st largest in terms of size in the night sky.
The constellation name means The Water Monster . The constellation is one of the original constellations that was devised by the Ancient Greco-Egyptian astronomer Ptolemy who lived between 90 A.D. and 168 A.D.
There are 20 stars that make up the main constellation. The hipparcos satellite scanned and detailed 3038 stars. There are 121 stars that can be seen with the naked eye in the constellation on a very clear night sky.
Hydra is not a member of the Zodiac group of twelve constellations that appear when the Sun sets. Hydra is a northern hemispheric constellation which means it can't be seen easily or at all from the southern hemisphere.
There are 32 Extrasolar Planets (Exoplanets) in this constellation that are detailed on this site. There is a dedicated page for exoplanets in Hydra. The current largest star so far identified in the constellation of Hydra is W Hydrae.
There are 3 deep space objects that were identified by Charles Messier in this constellation. There are no non-Messier deep space objects in this constellation that are covered at present on this site.
The image at the top right of this page was generated using Night Vision, a free to use and download application by Brian Simspon.
You can't just go to one location and arrive at the constellation because the constellation is made up of stars at different locations and different distances. The nearest main star in the constellation is at a distance of 100.98 light years and the furthest main star is a distance of 586.62 light years. The average distance to the main stars is 221.93 light years.
The caveat of these stars are that they are catalogued on this site. If you know of a star that is nearer or further then do let me know in the comments and I'll add it to the site. The stars mentioned are from the Hipparcos catalogue or have been added because of their special status.
The nearest star to Earth is Wise 0855-0714 which is roughly about 7.27 Light Years from the Earth. The nearest star to the Earth with an exoplanet is HD 90156 which is about 72.9 Light Years.
The furthest star that is located in the constellation is S Hydrae and it is 108721.1 light years away from the Sun. The furthest figure is derived from either the 1997 or 2007 Hipparcos star catalogue parallax figure and it has been known to produce distances that are wrong.
The brightest star in Hydra is Alphard and is located about 59.00 light years from the Sun. The star has a apparent magnitude of 1.99 but an absolute magnitude of -1.72 when the star is viewed from a distance of 10 Parsecs or 32.6 Light Years. The star is recognised as being the brightest in the constellation as it has the Bayer status of Alpha.
The dimmest star that can be seen in Hydra with the naked eye is HD 100623. The dim star has an apparent magnitude of 5.96. The dimmest star that a person is able to see with their naked eye is 6.0 magnitude based on the table in the reference. Ref: University of Michigan.
The constellation has a number of interesting variable stars labelled with a single letter. The brightest of these stars is U Hydrae which is a Magnitude 4 star and therefore is easy to see without visual aids. R Hydrae is on the cusp of visibility at Magnitude 6.4. V Hydrae is the only one of the three that can't be seen by the naked eye, you will need a good pair of binoculars to see.
All three stars are too far away for anyone to see the variability in the stars, you would need a very good telescope in order to see the star varying in size.
The snappily named SDSS 0907-0245 is an example of a Hypervelocity Stars, a star that is moving at above normal speed for a star. It is a star that got too close to the centre of the galaxy and thrown out. It will eventually become a rogue star, a star that is not within a galaxy.
Hydra is the undefeated largest constellation in the sky by area. It accounts for just over 3% which might seem a small amount but you need to take into account it is one of 88 constellations so it takes up more than its fair share of space. Hydra is a southern constellation lying south of the equator.
Hydra is the largest constellation in the sky and its not going to be easy to be able to always see it. The only time you are going to see the whole of it is in the Northern Hemisphere (London) is in May and June. The head will be visible in the northern hemisphere a lot longer than the rest of the body. The constellation disappears after June and then doesn't resurface until December.
Hydra is more visible in the southern hemisphere where you can see the start of the constellation from January. The whole constellation appears fully in the sky in an easterly direction. It rises high into the sky and then starts to dive under the horizon in May.
Hydra was a multi-headed sea creature that inhabited the lake near Lerna in the Argoid. It was alleged the lake had an entrance to the Underworld which it guarded. When one head was chopped off, another two would grow in its place. The only way of killing it was to chop off its head and setting fire to the severed neck. Hercules would chop off the head and Iolaus, a companion would set fire. During the fight, Hera set Cancer the crab to make things harder for Hercules.
There are 16 Meteor Showers that occur during the year within this constellation based on information gathered from Adam Mickiewicz University (Poland). The list below are major ones and which I have a date period for.
|Name||Activity||Peak Activity||Closest Star|
|nu Hydrids||19th March|
The following list contains the stars that make up the constellation. For a larger list of stars in the entire constellation area, please visit the For a list of named stars, that is stars that don't start HD or HIP, please visit Hydra Star List page.
|Name||Bayer||Distance (Lt.Yr.)||Right Ascension||Declination||Spectral Type||Colour|
|Alphard||Alpha Hydrae||180.30||09h 27m 35.25||-08d 39` 31.3||K3III||Orange|
|Beta Hydrae||Beta Hydrae||309.75||11h 52m 54.56||-33d 54` 29.3||Ap Si||White|
|Gamma Hydrae||Gamma Hydrae||133.84||13h 18m 55.25||-23d 10` 17.1||G8III||Yellow|
|Delta Hydrae||Delta Hydrae||160.36||08h 37m 39.41||+05d 42` 13.7||A1Vnn||White|
|Ashlesha||Epsilon Hydrae||129.28||08h 46m 46.65||+06d 25` 08.1||G0III-IV||Yellow|
|Hydrobius||Zeta Hydrae||167.18||08h 55m 23.68||+05d 56` 43.9||G8III-IV||Yellow|
|Eta Hydrae||Eta Hydrae||586.62||08h 43m 13.49||+03d 23` 55.2||B3V...||Blue/White|
|Theta Hydrae||Theta Hydrae||113.49||09h 14m 21.79||+02d 18` 54.1||B9.5V||Blue/White|
|Ukdah||Iota Hydrae||263.25||09h 39m 51.33||-01d 08` 33.6||K3IIIvar||Orange|
|Lambda Hydrae||Lambda Hydrae||112.55||10h 10m 35.40||-12d 21` 13.8||K0III||Orange|
|Mu Hydrae||Mu Hydrae||234.14||10h 26m 05.51||-16d 50` 09.9||K4III B||Orange|
|Nu Hydrae||Nu Hydrae||143.75||10h 49m 37.43||-16d 11` 38.9||K1.5IIIHdel-0.5 B||Orange|
|Xi Hydrae||Xi Hydrae||129.64||11h 33m 00.26||-31d 51` 27.1||G8III||Yellow|
|Pi Hydrae||Pi Hydrae||100.98||14h 06m 22.27||-26d 40` 55.3||K2III||Orange|
|Rho Hydrae||Rho Hydrae||354.14||08h 48m 25.98||+05d 50` 16.4||A0Vn||White|
|Minchir||Sigma Hydrae||372.76||08h 38m 45.45||+03d 20` 29.3||K2III||Orange|
|Zhang||Upsilon1 Hydrae||263.89||09h 51m 28.68||-14d 50` 47.6||G6/G8III||Yellow|
|Phi Hydrae||Phi Hydrae||210.56||10h 38m 35.01||-16d 52` 35.9||G8III||Yellow|
|Chi1 Hydrae||Chi1 Hydrae||141.01||11h 05m 20.03||-27d 17` 36.9||F3IV/V||Yellow/White|
|58 Hydrae||331.13||14h 50m 17.47||-27d 57` 36.8||K3III||Orange|
|Is a Zodiac Sign||No|
|Area||1302.844 sq. deg.|
|Percentage of Night Sky||3.16%|
|Site Exoplanet Count||32|
|Meteor Shower Count||16|
|Nearest Star||Wise 0855-0714|
|Nearest Star with Exoplanet(s)||HD 90156|
|Largest Star||W Hydrae|
|Dimmest Star||HD 100623|
|Furthest Star||S Hydrae|
|Bright Star Count||121|
|Hipparcos Star Count||3038|
|Main Star Count||20|
|Messier Deep Space Object Count||3|
|Bordering / Neighbouring / Surrounding Constellations||Crater|
*Note: The number of Non-Messier Deep Space Object Count relates to how many are covered on this site not how many there are.
|Ghost of Jupiter (NGC3242)||Planetary Nebula||-18:38:32.6||10h 24h 46m 1|
|Messier 48 (NGC2548)||Globular Cluster||1500||-05:48||08h 13m 8|
|Messier 68 (NGC4590)||Globular Cluster||33600||-26:45||12h 39m 5|
|Messier 83 (NGC5236)||Spiral Galaxy||14700000||-29:52||13h 37m 0|
|NGC 2850||Galaxy||-04 56 24.28||09 20 56m 997|
|NGC 3309||Giant Elliptical Galaxy||-27 31 06.35||10 36 35m 651|
|NGC 4993||Elliptical or Lenticular Galaxy||130 Million LY||-23d 23` 4||13h 09m 47m 2|
|Porpoise / Penguin Galaxy||Galaxy||326 Million LY||+2d 46` 00||09h 37m 41|
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