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 Perseus arm 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 two swooping 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 1.5 million years old -- in the centre of the nebula is known as Melotte 15. The nebula 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 Soul Nebula. Inside are several open clusters, containing several generations of stars: older stars in the hollows of the nebula's cavities (red), and younger stars lining the rims (green). Astronomers believe that when the older stars formed, the intense activity pushed the gases outward into the dense clouds indicated by the green regions. In turn, this activity caused new bursts of star formation in 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, had to go and stuff it all up by boasting that Andromeda was more beautiful than the 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 demigod Perseus, slayer of the Gorgon Medusa, was having none of that; he fearlessly slaughtered the monster, rescued Andromeda and married her, because nothing says true love like a chap slaying the slavering behemoth about to eat you alive. Upon her death, she was placed in the sky, near to her true love forever (and her mum, who may have been foolish but nevertheless loved her daughter very much).
Andromeda is quite a distance from the galactic plane, and therefore contains no nebulas or clusters. What it does contain is the Andromeda Galaxy -- the Milky Way's closest major galactic neighbour, and the largest galaxy in the Local Group, both in terms of size and mass.
Were Perseus to pluck a flower for his Andromeda, he might look no farther than NGC 2237 -- the Rosette Nebula, so named for its resemblance to the many-petalled flower of blushing love. Located in the constellation 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 million years old -- whose winds and radiation are sculpting the nebula’s complex petals.
When galaxies veer too close to each other, their mutual gravitational pulls drag at their shapes, pulling them out of true.
Arp 273, 300 million light-years away and visible through the constellation of Andromeda, is just such a phenomenon. Two galaxies are aligned in such a way that they seem to form the shape of a graceful stemmed rose. The larger of the two galaxies, UGC 1810, five times the mass of its companion, is a spiral galaxy whose shape has been distorted by the smaller galaxy, UGC 1813, below.
The large outer arm of UGC 1810 appears partially as a ring. This feature is usually seen when one galaxy passes through another -- indicating that UGC 1813 dived through UGC 1810, rather than being consumed by it.
In the upper right section of UGC 1810, another unusual feature is visible -- what seems to be a mini-spiral.
Coma Berenices -- formerly an asterism, and now officially recognised as a constellation -- is a collection of faint stars around 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 safely from 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, the shorn locks were transported to the heavens to be immortalised as glittering stars.
Although it is small and faint, Coma Berenices is actually a very rich section of the sky. It contains eight Messier objects and a large number of galaxies, containing both the Coma Cluster -- one of the densest known clusters of galaxies, containing over 1,000 -- and the northern section of the Virgo Cluster of galaxies. It also contains several globular clusters.
One of the brightest objects in the sky -- visible to the naked eye even during daylight, and third only behind the sun and moon -- is Venus, the second planet from the sun and the closest planet to Earth, named for the ancient Roman goddess of love, victory, fertility and beauty. Close by to Venus in the sky is a star cluster called Pleiades -- the seven sisters of Greek mythology -- named for its very bright stars (there are actually nine of these; the two extra stars are named after the sisters' parents).
Although a planet named after the goddess of love sounds like a wonderful place, Venus is actually highly inhospitable. It's covered by thick layers of toxic cloud -- these are what make it so bright, as they are highly reflective. They're also composed of sulphur dioxide and their thickness creates the strongest greenhouse effect in the solar system. Even if humans could breathe Venus' carbon dioxide and nitrogen atmosphere, we'd rapidly be crushed or burn to a crisp. Venus' atmospheric pressure at the surface is 92 times that of Earth, and its minimum surface temperature is 735 Kelvin (863 degrees Fahrenheit). Not a single probe sent to Venus has made it to the surface intact or even functional.
Best just to look up, make a wish and admire the glittering beauty from a safe distance.
The Necklace Nebula -- 15,000 light-years from Earth in the constellation of Sagitta, glittering like a string of gems in the darkness of space -- is pretty small as far as nebulas go, measuring just 2 light-years across and 9 light-years long. We've included it here not for its resemblance to jewellery (although it would be pretty amazing to wear something so spectacular), but for the way in which it formed.
The bright star in the centre of the nebula is actually two stars -- a binary system. About 10,000 or so years ago, the larger star expanded to the point where it engulfed the smaller star, which remained intact, orbiting inside its larger companion. This increased the larger star's spin to such a degree that a large part of its gaseous envelope flew off into the space around the pair, forming a planetary nebula -- with most of the gas distributed around the star's equator, due to centrifugal force, forming the "necklace" for which the nebula is named.
The two stars continue to orbit each other furiously, with each orbit taking just over a day. Eventually the two cores will merge, either forming a new, single star or resulting in a brilliant supernova.