All this data is potentially out of date, and should be taken with a truckload of salt
A cynosural field, also known colloquially as a "cyno", is a cosmic anomaly that acts as a pseudo-gravity well. With the correct calibration information, interstellar jump drives can lock onto the field and create a portal into the destination system.
Cynosural field generation requires the user have levels in Cynosural Field Theory. Remote generation of cynosural fields is not currently possible. Thus, capital pilots must rely upon another pilot to generate a cynosural field in the target system. When activated, cynosural fields act as beacons, allowing any pilot in the system to locate and warp to the field.
Jump drives rely upon out-of-band faster-than-light communications in order to calibrate and lock onto a cynosural field. Because of this, both the cynosural field generator and jumping pilot must be in the same fleet to use the cyno. This information is broadcast once when the cynosural beacon is lit, but can be rebroadcast by clicking the white triangle at the top of the fleet window. By relying upon FTL communications, only authorized pilots (those in your fleet) will be able to jump to the same field, preventing an enemy capital fleet from jumping to a friendly cynosural field.
Cynosural fields can also be generated on a continuous basis by using a Cynosural Generator Array. Such generators require an alliance to have appropriate sovereignty to use. These generators operate on a constant basis, broadcasting the appropriate calibration information out-of-band via the alliance channel, allowing any pilot in that alliance to lock onto the generator's field.
A cynosural field will usually last for 10 minutes.
Force recon ships have a special skill that will reduce the cynosural field duration to 5 minutes. Also, they have a special bonus that will reduce the amount of liquid ozone required for generating a cynosural field.
Generating a cynosural field is a highly taxing operation. In addition to requiring a certain amount of liquid ozone to create the field, all the ships resources must then be concentrated on maintaining the field. This is at the expense of weapons, navigation, and defensive systems, all of which are disabled while the field is active. This leaves the generator extremely vulnerable to attack. Once the field collapses, the generator regains full control of their ship.
This makes the placement of a cynosural field extremely important. Activating a cynosural field in a safespot is not a good decision as the beacon created by the field will alert all pilots in system to the location of the safespot. There are two generally accepted locations that are good for placing a field: friendly starbases (POS) and stations.
At a Starbase
Placement of a cynosural field at a friendly POS can be achieved either with the ship-based Cynosural Field Generator or with an anchored Cynosural Generator Array. This generally ensures that there will be protection for the field generator and jumping ship. The turrets and other defensive equipment can be used to attack anyone approaching the field, giving the jumping ship enough time to get into the protective force field of the POS or to warp to another protected location. Cynosural fields cannot be activated within the protective force field. Additionally, the incoming jumping ship will not have the appropriate force field password set on jump-in, so placing the field too close to the force field may result in the jumping ship being forcefully ejected from the force field, leaving the ship highly vulnerable. Generally, a well accepted location to activate a field is about halfway between the force field and a grouping of turret/missile batteries.
At a Station
Another viable location for locating a cynosural field is at a station or outpost. The key here is to select a station with a large docking radius, but an area that is generally devoid of the actual station structure. Such locations are often found above or below the station or just off the undock point. When placing the cynosural field, the generator should be close enough into the docking ring such that the jumping pilot can immediately dock after the session timer expires, but far enough from the station structure such that the jumping pilot's ship won't be forcefully ejected from the station. This can be a vulnerable location for the field generator, however, as there are little or no protections at stations to prevent an immobilized generator from being attacked and destroyed.
Jumping to a cyno
Ships that jump to a cyno will appear at a random location within a radius of 15 kilometers of the cynosural beacon.
Cynosural fields can be jammed through the use of specialized equipment. The major empires use technology of this sort to prevent the generation of cynosural fields in systems with a security status of 0.5 or greater. Alliances that have sovereignty 3 or greater in a system can deploy a Cynosural System Jammer at one of their starbases in that system. When online, the jammer prevents any cynosural fields from being generated including any friendly one. This allows the sovereign alliance greater control over who may access the system via capital ships.
The Cynosural System Jammer can be temporarily disabled and reactivated to allow friendly cyno's to be activated. Great care must be used when trying such tactics, since reactivating the jammer requires some time during which enemies can also activate their own cynos.
The most effective way to stop enemies for using a cyno is to quickly target and destroy the cyno generating ship before any hostile capital ship has managed to jump to the cyno beacon. With the destruction of the cyno generating ship, the cyno beacon will also disappear.
Logging off after lighting a Cynosural Field
If a character lights a cyno and logs off shortly thereafter, while the Cynosural Field Generator cycle is still active, the server will treat this pilot as being online until the cycle completes. This means that the ship will linger in space for the full duration of the module cycle, and if aggressed by another player character within the cycle, will receive a full 15 minute PVP logout timer.
More info on the PVP logout timer can be found here: http://wiki.eveonline.com/en/wiki/PvP_Logout_Timer