Danesol, The Sun is a common all garden Yellow Dwarf star, classification dG2V, meaning it is a DWARF G2 Main Sequence Star.
The G2 comes from the colour classification which relates to the surface temperature of the Star;
O = White Stars with surface Temperatures of 40,000K - 120,000K
B = White/Blue Stars with Surface temperatures of 20,000K - 40,000K
A = Blue/White stars with Surface Temperatures of 8500K - 20,000K
F = Yellow/White stars with surface temperatures of 6500K - 8500K
G = Orange/Yellow Stars with Surface temperature of 5200 - 6500K
K = Red/Orange Stars with surface temperatures of 3000K - 5200K
M = Red stars with surface temperatures of 1500K - 3000K
Each of these classification is then sub-divided into 10 sub groups, for example A0 - A9 (The lower the number indicates the lower surface temperature)
Now as I said, the Sun is a G2 type star, this means it has a surface temperature of around 5600K and sits of the edge of the G2 and G3 classification region
This will help visual this;
Fig 1: Size/temperature relationship: A Hertzsprung-Russell Diagram
In this diagram the Limiting distance refers to how far the star can be seen from in kilo-parsecs (1 parsec =3.26 light years) and the Absolute Magnitude refers to how bright the star would appear from 10 parsecs (32.6 light years).
This diagram is very simplified and is not totally accurate, but good enough for this. Recent research is questioning the "Helium Flash" actually happens and this diagram also misses out the Galactic Hypergiants, stars that exceed 65 solar masses.
Here is one showing the Sun in relation to other well known stars.
Fig 2: Solar comparison diagram.
Now the Sun used to be thought of as a constant star, that is output only varied by tiny amounts over geological time, this is why back in the 1840's they came up with the so called "Solar Constant", which was a measure of the total output of the Sun as received by a given area of the surface of Earth over a measured period of time. Fairly rapidly, as measuring techniques improved, they discovered that the output of the Sun varied by an average of 0.2% over the same 11 year period that had been known for thousands of years and determined by Chinese and European (later) observers recording the amount of "Sun spots", so called dark regions, on the visible surface of the Sun.
Much research has been done in recent years with regards to this so called constant, which is now known to be anything but, and further, it has been discovered that the solar 11 year cycle is likely part of a much longer period cycle that sees the Solar output vary by up to 2% over a period that may be as much as 100,000 years. To make this even more complicated, we are just discovering that within this there are other periods of variability that impact the energy we receive on Earth, and that the solar 11 year cycle virtually shuts down for long periods.
Such a period was recorded in the middle ages, known as the Maunder Minimum, this was a period of frigid winters and poor summers in the Northern Hemisphere for some 250 years, with tidal rivers, such as the Thames and the Rhure actually freezing in winter for several months. This period is also know as "The Little Ice Age". This period was not unique, several distinct periods have been identified in human history where prolonged cold spells are matching changes within the Sunspot count on the surface of the Sun.
Currently the Sun is at a maximum period of activity for the current cycle, however this maxima is actually below the minimum levels recorded during the periods from 1860 to 1990 and is a likely explanation for the frigid temperatures recorded in Northern regions over the last decade. Scientists do not know if this will be a poor cycle or actually the start of a prolonged slow down of this cycle before it starts again, if it's the latter then we can expect temperatures in the UK to drop to around -30°C in winter and rise no higher than around +10°C in summer as the cycle deepens, although how long that will take is anyone's guess as there is not enough historical data to give a conclusive guide.
As a backdrop to all this, the solar radiation received from the Sun will increase over time, as the Sun uses up more and more of the Hydrogen fuel in it's core the core will cool, this will cause gravity to crush it, increasing pressure and thus pushing the distance between the energy production and the convective zone further apart, causing the outer layers to cool, however this will cause them to also expand, thus the actual radiative energy released from the surface will increase, however this will not happen for about 1.5-2 billion years, and we will be long forgotten as individuals and as a species...
