Question: How long does an orbital cycle take?
About the article "Global warming", section "Initial causes of temperature changes (external forcings)".

Candidate passages:
al period.
The orbital period is simply how long an orbiting body takes to complete one orbit. 
Annual cycle refers to the set of changes or events that uniformly, or consistently, take place at the same time of year.
In biology, the annual cycle for plants and animals details behaviorial and chemical changes that take place as the seasons advance.
In religion, the annual cycle refers to the various celebrations or memorials that occur in the same sequence from year to year.
For example, Christianity has two annual cycles, the "temporal cycle" that tracks the events in the life of Christ, and the "sanctoral cycle" which tracks the various saint's days.
Some Christian churches only observe the "temporal cycle".
In climatology, an annual cycle is the part of a measured quantity's fluctuation that is attributed to Earth's changing position in orbit over the course of the year.
Such quantities might be influenced directly (e.g.
incoming solar radiation at a point at the surface) or indirectly (e.g.
stratospheric westerlies and easterlies over the winter and summer hemispheres, respectively) by orbital position.
Mathematically, the climatological annual cycle is commonly estimated from observational data or model output by taking the average of all Januaries, all Februaries, and so forth.
If the observational record is long enough and conditions are stationary (i.e.
there is no significant long-term trend), a meaningful annual cycle will result that can be used to calculate an anomaly time series. 
It has long been a dream that some day in the future, orbital spaceplanes may take off, ascend, descend, and land like conventional aircraft, providing true single stage to orbit (SSTO) capability, at commercial airline prices.
Proponents of scramjet technology have claimed that 100 percent scramjet powered vehicles will make this kind of SSTO flight possible.
Unfortunately, no one has been successful in making that happen.
However combination designs have been proposed that combine rockets, with ramjets, and scramjets, in a single vehicle, and these may be easier to design and build.
This type of propulsion system is called RBCC, which stands for Rocket Based Combined Cycle.
Another type of combination vehicle uses what is called a TRCC propulsion system.
TRCC stands for Turbo-Rocket Combined Cycle which is an after-burning turbine engine combined with an RBCC propulsion system.
The main problem with SSTO vehicles is the high propellant fraction which drives up the overall weight of the spaceplane to unworkable amounts. 
Transits sometimes repeat after 13062.8 days (about 35 years and 9 months).
This corresponds to 15.998 Mars-Jupiter synodic periods, or 19.01 Mars orbital periods, or 3.01 Jupiter orbital periods.
However, in many cases, the transit does not repeat because the second event is a near-miss instead.
This period is analogous to the 8-year pairing of transits of Venus.
Longer cycles with a closer match are a cycle with an approximately 56,333-day (about 154 years and 3 months) period that is equal to 69 Mars-Jupiter synodic periods and a cycle with an approximately 212,273-day (about 581 years and 2 months) period that is equal to 260 Mars-Jupiter synodic periods. 
In orbital mechanics, mean motion (represented by formula_1) is a measure of how fast a satellite progresses around its elliptical orbit.
Unless the orbit is circular, the mean motion is only an average value, and does not represent the instantaneous angular velocity.
In databases of satellite orbital parameters the mean motion is typically measured in number of revolutions per day.