Today, I would like to talking a little about the process of reconstruction and the way we view the Theoi in Hellenimsos. This post is part of the beginner's guide to Hellenismos.

Modern worshippers of the Theoi--myself included--often try to compartmentalize Their worship. This, because we aren't raised in a culture where the Theoi are worshipped in grand festivals and we have to reinvent the wheel as we try to find ways to worship Them in a way that resembles the ways of the ancient Hellenes. To have some hard rules for this worship helps us greatly; it allows us to look at the parts of the rites we do know and infer the rest--at least in broad lines. The biggest boxes we use are 'Ouranic' and 'Khthonic', and we often think the two are entirely separate--they are not.

'Ouranic' is a term that applies to Theoi and practices who reside or that are associated with Mount Olympos, home of many of the Theoi. As such, Ouranic deities are also referred to as 'Olympians'. In ancient Hellas, an altar for the Ouranic Theoi was called a 'bômos' (βωμός). Most bômoi were isolated cubes, around one meter (three feet) high, but there were altars which were far larger. The sacrificial altars were either square or round, and many held an 'epipuron' (ἐπίπυρον)--a movable pan or brazier, used on top of the bômos so it could serve as an altar for burnt-offerings. Impromptu altars for the Ouranic deities were made of earth, turf, or stones collected on the spot. What mattered was that the offering was sacrificed (high) off of the ground.

Ouranic deities tended to receive wine libations that were mixed with water. Food offerings were usually divided between the Theoi and the worshippers where only a ceremonial part of the sacrifice was given to the Theoi. In general, Ouranic-themed festivals were light in tone and included a measure of festivity. They were also conducted at temples, often within the city limits. Sacrifice to the Ouranic deities was given with hands raised high, up towards the sky, with the palms flat and up. Worshippers stood for the sacrifice, and they were given during the daylight hours of the festival day.

'Kthonic', on the other hand, refers to deities or spirits of the Underworld or the earth, and the rituals associated with Them. An 'eschára' (ἐσχάρα) is the term for a low-lying altar used in burnt-offerings  for the Khthonic Theoi. An offering pit--'bothros' (βόθρος) in Greek texts--also sufficed. Khthonic deities received either wineless libations (water, milk, and honey, usually), or wine libations of unmixed wine. These rituals often took place outside of the city walls, or started within the city walls ad ended outside of it. Their tone was usually sombre or grim, and there was far more fear of the Theoi invoked. Truly Khthonic sacrifices involved kneeling, and/or lowering or striking the flat palms either on or towards the ground. They were held at night and the sacrifices were given whole; it was a holókaustos (ὁλόκαυστος), and the matching libation a khoe (χοαί). The whole offering was either burned or buried and no one partook of any of the food or drink that was given to the Khthonic Theoi. This because contact with the underworld carried miasma.

Miasma (Μίασμα) literally means 'pollution', and it describes the lingering aura of uncleanliness in regards to a person or space through which contact is made with the Gods. Next to piety, being ritually clean is one of the most important things to adhere to within Hellenismos. Miasma occurs whenever the space or person comes into contact with death, sickness, birth, sex, excessive negative emotions and bodily fluids (amongst a few others). Especially death and birth, because these acts open up of the way to the Underworld. When a Khthonic deity is invoked, this passageway is opened as well.

Ouranic deities cannot and will not come into contact with the Underworld. They must remain pure, untainted. If a worshiper is tainted with miasma, he or she must first clean themselves of it through katharmos ((Καθαρμός). The most well-known of these is through applying khernips (Χἐρνιψ). Khernips is created by dropping smoldering incense or herb leaves into (fresh and/or salt) water (preferably sacred spring water or sea water). Both hands and face are washed with khernips.

There are, however, entities that exist between the strict divide between Ouranic and Khthonic, and the rites that honour them are mixed as well. Heroes were often worshipped at the eschára, for example, and certain Gods walk the fine line; Hekate, for example, who walks freely between the upper world and the Underworld, or Persephone, who spends part of the year in the Underworld and the rest on Olympos with her mother and father. And then there are Theoi like Zeus and Hermes, who have certain epithets that can make the journey down, and Hades who has an epithet who can make the journey up.

An epithet is an attachment to the name of a God or Goddess, used to indicate either a specific domain of the Deity, a specific origin myth or region from which the Deity came, or an entirely different entity, through either domain or origin. Epithets serve(d) either a ritualistic function or a literary on; hymns and chants are used in both aspects of Hellenismos and in both, destinctions are made between the various epithets of the Gods. 
Within ritual, epithets are used out of respect, devotion and out of practicality. It's seen as respectful to address the Gods by their various names. It shows you are aware of the names of the Gods as well as the domains They influence. As for the practical; well, some Gods rule over a variety of domains. Zeus, for example guards travelers in His epithet of Zeus Xenios but is seen as the bringer of storm-clouds in his epithet of Zeus Ombrios. It's rather obvious, but getting rained upon is probably not what you were after when asking Zeus for aid on your journey.
In general, Khthonic deities have epithets that make them less scary and more helpful to humanity, and then there are Ouranic deities who have darker epithets. Ploutōn (Πλουτων), as an epithet for Hades, was venerated as a stern ruler but the loving husband of Persephone. The couple received souls in the afterlife, and are invoked together in religious inscriptions. Hades by contrast had few temples and religious practices associated with Him, and was portrayed as the dark and violent abductor of Persephone. Ploutōn was viewed as a harvest God, and prayed to for prosperity. The other way around, Hermes has his epithet 'Khthonios', in which he guides the souls of the dead down to the Underworld. Zeus has his epithet of 'Meilichios', and it was one of His most popular ones.
Meilichios (Μειλίχιος), meaning 'Kindly One', is a Khthonic epithet of Zeus, who generally receives nighttime sacrifices, and only by way of a holókaustos. Zeus seems to have adopted the Meilichios epithet from an older Khthonic serpent daímōn or Theos. He is considered a purifier. In fact, during the Diasia--a festival held at the end of winter, a time where many festivals linked to ritual purification were held--the members of the household would touch a sacrificial animal before it was sacrificed, believing the miasma they carried would be transferred into it and then burned away. Old practices for Hekate's Deipnon included the same to be done with a dog.
Theoi that mixed Khthonic with Ouranic markers (or the other way around) also tended to have mixed rites performed in Their name. The aforementioned Diasia, for example was held during the daylight hours of the festival day. The sacrifice was given on a raised altar made of stone found in the area, but it was performed outside of the city walls. It was a holókaustos sacrifice, but there was a big picnic-type feast held afterwards with other foodstuffs that people brought. The sacrifice itself was sombre and gloomy, but the day ended with good food and gifts for kids, making it a favourite amongst huge amounts of people. Its function was to lift the burden of miasma from the worshippers, but in doing so, a way to the Underworld had to be opened; a mixed bag for sure.
As much as we, as Hellenists, would like to create boxes and labels for the Theoi and Their worship, there will always be instances where the lines are blurred and it's important to realize that for the ancient Hellenes, these lines would not have existed--and if they did, they evolved with every generation. Our religion is far more flexible than we would perhaps like it to be, but therein lies its beauty: the ancient Hellenes found ways to include the most powerful and most beloved Theoi in the rites that mattered most to them. They created loopholes and reasons within the framework of their religion to do what they perhaps felt to be the right thing. This flexibility is hugely important to remember for modern practitioners lest we get bogged down in rules that never existed, and the dichotomy between Ouranic and Khthonic is one of them.