Solar Eclipse

Event
The Solar Eclipse is an event occurring only in Hardmode. It is announced at the beginning of a day with the message, "A solar eclipse is happening!", lasting from sunrise to sunset. During the Solar Eclipse the light will be only slightly brighter than at night and you can see the moon in front of the sun.

It is similar to a daytime, hardmode version of the Blood Moon, and should be treated as such.

Unique Enemies
All of these have high HP and high damage, and some of them have special features that make fighting them extremely hard. It is recommended to treat this event as a Boss fight mixed with an Invasion, since there will be large numbers of very tough and unusually agile enemies, most of which are resistant to knockback.

Players wishing to avoid the creatures spawned by this event can easily do so by burrowing underground, which prevents Eclipse enemies from spawning altogether, or by staying inside a floating house, since only the Reapers can pass through walls and they have the same shortcomings as Wraiths, namely, they can only ascend when inside a block.

Tips

 * One effective strategy is to plant Tiki Torches to light up the area, and then use the Flamethrower to eliminate enemies. Since the flamethrower reduces forward movement, this will cause it to incinerate entire groups at once, making the Eyezor the only real threat. If you have time, prepare the arena to include two short 'mounds', which will protect you from the Eyezor until it hits the top of the 'mounds' you have created, though this will allow the Reapers to have more cover as they move through the 'mounds.'
 * Another useful setup is a Paladin's Hammer plus Titan Glove (or one of its derivatives), since the extremely high speed and knockback allow the player to keep enemies away while dishing out serious punishment. This setup is more click-happy than the previous one though, and Eyezors are still a threat.
 * The Mushroom Spear is also quite effective. The spinning mushrooms deal quite a lot of damage when the mobs run through them. All knockback bonuses are of use, either through reforging or by accessories like the Titan Glove.
 * The Chlorophyte Shotbow may be your best friend if you are a ranged character. Even with standard Wooden Arrows, the multiple arrows fired per click all but neutralize the enemies' resistance to knockback, as well as dealing heavy damage.
 * Another effective strategy is to get Spear traps from the Lihzahrd dungeon. Make a 6-8 tile deep by 7 long pit, have the Spear Traps above the pit, pressure plates in the pit and make a little tunnel below the pit to collect the loot from the mobs. Does not work with Reapers.
 * using the piranha gun proves extremely effective as its nockback can cause the enemies behind the target to pile up all receiving continual damage and being stunned for the most part, so long as it is used on the target closest and the player continually switches sides to avoid getting attacked from behind.
 * if you're looking to acquire the broken hero sword it can be a good idea to have a water candle in your hot bar to switch to during times without enemies, it will help to have a steady flow of enemies without overwhelming you like the battle potion.

NPCs

 * The Cyborg will sell Rocket IV

Trivia

 * Some enemies seem to be based off old horror movie creatures. Vampire resembles Bram Stoker's Dracula and Frankenstein is Frankenstein's Monster. Swamp Thing is, well, Swamp Thing (from DC Comics). Reaper and Eyezor don't seem to have a basis in old Horror Movies though.
 * It is not a total solar eclipse. It is actually an annular ring eclipse, when the moon is not quite close enough in its orbit to cover the entire sun. The moon has a elliptical orbit around the Earth, being closer or farther in its orbit at times. The moon also revolves around Earth at a 5 degree plane, where as if it was at a 0 degree plane, you would have a Solar Eclipse every lunar month.
 * The music that plays during an eclipse is the 'Terraria 1.2 Update - Music Spoiler' that Red uploaded to his Youtube Channel 'Demilogic' (http://www.youtube.com/user/demilogic?feature=watch) on August 10, 2013.

History
(Not actually working despite Developer tweet.)