Cosmic love: Romance among the stars (pictures)

With Valentine's Day approaching, romance is in the air -- way, way up in the air. It's not just humans who like to show their affection. So do cosmic bodies.

Located in the constellation of Cassiopeia in the Perseusarm of the Milky Way galaxy and some 7,500 light-years from Earth is IC 1805, aka the Heart Nebula. The reason for this name should be obvious: its twoswooping wings resemble the shape of a heart, and it glows red from within --classifying it as an emission nebula -- from hydrogen ionised into plasma by nearby stars. The cluster of very young, hot stars -- just 1.5million years old -- in the centre of the nebula is known as Melotte 15. Thenebula itself spans some 200 light-years across.

Where you find heart, you'll also find soul. To the east of IC 1805 is Westerhout 5, also known as the SoulNebula. Inside are several open clusters, containing several generations of stars: olderstars in the hollows of the nebula's cavities (red), and younger stars liningthe rims (green). Astronomers believe that when the older stars formed, theintense activity pushed the gases outward into the dense clouds indicated bythe green regions. In turn, this activity caused new bursts of star formationin the newly formed dense areas.

Poor Andromeda got a bit of a raw deal. Sure, she was a beautiful princess, but then her mum, Cassiopeia, hadto go and stuff it all up by boasting that Andromeda was more beautiful thanthe Nereids. You know, Poseidon's posse. Enraged, the god of the sea sent a sea monster to lay waste to Cassiopeia's land...her response to which,apparently, was to pacify the monster by sacrificing poor Andromeda. Brave demigodPerseus, slayer of the Gorgon Medusa, was having none of that; he fearlesslyslaughtered the monster, rescued Andromeda and married her, because nothingsays true love like a chap slaying the slavering behemoth about to eat you alive. Upon herdeath, she was placed in the sky, near to her true love forever (and hermum, who may have been foolish but nevertheless loved her daughter very much).

Andromeda is quite a distance from the galacticplane, and therefore contains no nebulas or clusters. What it does contain isthe Andromeda Galaxy -- the Milky Way's closest major galactic neighbour, and the largestgalaxy in the Local Group, both in terms of size and mass.

Were Perseus to pluck a flower for his Andromeda, he mightlook no farther than NGC 2237 -- the Rosette Nebula, so named for itsresemblance to the many-petalled flower of blushing love. Located in theconstellation of Monoceros (Greek for unicorn), some 5,200 light-years from Earth,the multipart emission nebula is also an active stellar nursery. At its core(50 light-years across) is an open cluster of young stars -- only 4 millionyears old -- whose winds and radiation are sculpting the nebula’scomplex petals.

When galaxies veer too close to each other, their mutualgravitational pulls drag at their shapes, pulling them out of true.

 Arp 273,300 million light-years away and visible through the constellation ofAndromeda, is just such a phenomenon. Two galaxies are aligned in such a way that they seem toform the shape of a graceful stemmed rose. The larger of the two galaxies, UGC1810, five times the mass of its companion, is a spiral galaxy whose shape hasbeen distorted by the smaller galaxy, UGC 1813, below.

The large outer arm ofUGC 1810 appears partially as a ring. This feature is usually seen when onegalaxy passes through another -- indicating that UGC 1813 dived through UGC1810, rather than being consumed by it.

In the upperright section of UGC 1810, another unusual feature is visible -- what seems tobe a mini-spiral.

Coma Berenices -- formerly an asterism, and nowofficially recognised as a constellation -- is a collection of faint starsaround the north galactic pole. It's one of the few constellations named for a real person-- Queen Berenice II of Egypt -- rather than a mythological figure. Legend has it that Berenice,in a desperate bid to ensure her husband Ptolemy III Euergetes' return safelyfrom war, promised her beautiful flowing golden hair -- the pride of Egypt --to Aphrodite in sacrifice. Upon Ptolemy's safe return, she kept her promise,whereupon the goddess was so moved by the queen's sacrifice to her love, theshorn locks were transported to the heavens to be immortalised as glitteringstars.

Although it is small and faint, Coma Berenices is actually avery rich section of the sky. It contains eight Messier objects and a largenumber of galaxies, containing both the Coma Cluster -- one of thedensest known clusters of galaxies, containing over 1,000 -- and thenorthern section of the Virgo Cluster of galaxies. It also contains several globular clusters.

One of the brightest objects in the sky -- visible to thenaked eye even during daylight, and third only behind the sun and moon -- isVenus, the second planet from the sun and the closest planet to Earth, namedfor the ancient Roman goddess of love, victory, fertility and beauty. Close by to Venus in the sky is a star clustercalled Pleiades -- the seven sistersof Greek mythology -- named for its very bright stars (there are actually nine ofthese; the two extra stars are named after the sisters' parents).

Although a planet named after the goddess of love soundslike a wonderful place, Venus is actually highly inhospitable. It's covered bythick layers of toxic cloud -- these are what make it so bright, as they arehighly reflective. They're also composed of sulphur dioxide and theirthickness creates the strongest greenhouse effect in the solar system. Even ifhumans could breathe Venus' carbon dioxide and nitrogen atmosphere, we'd rapidlybe crushed or burn to a crisp. Venus' atmospheric pressure at the surface is92 times that of Earth, and its minimum surface temperature is 735 Kelvin (863 degrees Fahrenheit). Nota single probe sent to Venus has made it to the surface intact or evenfunctional.

Best just to look up, make a wish and admirethe glittering beauty from a safe distance.

The Necklace Nebula -- 15,000 light-years from Earth in theconstellation of Sagitta, glittering like a string of gems in the darkness ofspace -- is pretty small as far as nebulas go, measuring just 2 light-yearsacross and 9 light-years long. We've included it here not for itsresemblance to jewellery (although it would be pretty amazing to wearsomething so spectacular),  but for the way in which it formed.

The bright star in the centre of the nebula is actually twostars -- a binary system. About 10,000 or so years ago, the larger starexpanded to the point where it engulfed the smaller star, which remainedintact, orbiting inside its larger companion. This increased the larger star'sspin to such a degree that a large part of its gaseous envelope flew off intothe space around the pair, forming a planetary nebula -- with most of the gas distributed around the star's equator, dueto centrifugal force, forming the "necklace" for which the nebula isnamed.

The two stars continue to orbit each other furiously, witheach orbit taking just over a day. Eventually the two cores will merge,either forming a new, single star or resulting in a brilliant supernova.