Aura is the positively charged magical background radiation, making it the counterpart of Taint.
To first understand what the aura is, you need to understand what Vis is. Vis is the magical energy inherent in all things. Every living thing and every piece of inanimate matter contains a certain amount of Vis. The rarer or more powerful the object is, the greater the amount of Vis it contains. When a creature dies or an object is destroyed this Vis is released into the atmosphere where it remains until it is reabsorbed by items and creatures.
The Aura is this latent background Vis energy that is not trapped within an object or a creature. If an area has a particularly high Aura rating, the Vis tends to naturally siphon into areas with lower vis ratings, thus distributing a high Vis concentration pretty fast.
The Aura of a given area can be tapped by a Vis Condenser and turned into liquid Vis for use in other alchemical devices. The amount of Aura in an area is finite however, and using too much of it can have fateful consequences: The higher an Aura is, the more living things thrive there. Areas with low aura ratings tend to be lifeless and barren.
Measuring the AuraEditYou can measure the charge level of the local Aura with the Vis Detector, the Thaumometer and the Goggles of Revealing. If you have a Vis Detector or a Thaumometer in your inventory or your hotbar, a Vis Gauge will appear on the lower right of the screen. This gauge indicates the total percentage of background Vis of the chunk you are currently in.
When the button below the gauge is glowing, it means that some background effect like hidden crystals or Vis sipping in from a neighboring chunk with a higher Vis concentration is positively affecting the aura.If you have a pair of Goggles of Revealing, you can see the precise amount of Vis (and Taint) currently present in the atmosphere. The percentage to the right of the Aura and Taint buttons indicates whether some changes to the Aura and Taint levels are currently going on.
Regenerating the AuraEdit
First and foremost, you're generally advised not to let the Aura of an area drop down to dangerous levels in the first place. Once the Taint gets a hold in an area, it is very time- and resource-consuming to clean up. That being said, if you can "inject" Vis into the Aura by throwing potions of Concentrated Vis to the ground. Each potion will inject about 200 units of Vis into the Aura. You should keep in mind that this Vis will most likely siphon into the neighboring areas though, so you should prepare a large batch of potions. As a safeguard, you can also plant several Vis Crystal Ores in the area to ensure that the aura is able to regenerate itself once it falls below ten percent.
If you have some Silverwood Logs to spare, you could also use them to craft some Totems of Dawn and place them in the area. They will not only prevent taint from forming and/or proceeding further, but they will also positively influence the Aura and decrease the amount of Taint.
Effects of the AuraEdit
Once an area contains enough aura, certain things happen. If this is the case in a desert, the sand will slowly convert to dirt, then into a grass block with a chance of spawning tall grass. This can be annoying as these changing blocks count as block updates, and the desert will be filled with holes if the sand falls into a cavern. However, these holes are helpful in finding near-surface dungeons.
Another interesting effect of high aura is that logs that do not have leaves connected, say player placed logs or AI built logs, will grow a small cube of leaves around it.