The general consensus on the orientation of Stonehenge is that it was aligned towards the summer solstice sunrise (also referred to as midsummer, the longest day of the year) to perfectly frame the Sun between the 'entrance' to the Sarsen Circle. The Heel stone was then placed on this axis of alignment in such a way that the Sun rose directly over the top of it. Indeed, this makes for the most remarkable of photos. However, it is a lie! As author Christopher Chippindale admits:

You can see the effect for yourself by clicking here. Other authors have claimed numerous alignments towards celestial events, many of which belong to Celtic tradition, but the fact is at present Stonehenge aligns to nothing without the addition of five odd stones placed on or outside the Bank (two of which are missing). If these events were so important could we not expect to see the entire collection of 40 Sarsen pillars so aligned that the purpose of the site was beyond any doubt?
 

In my book, The Stonehenge Observatory, I suggest Stonehenge was originally aligned North at latitude 45ºN and that a major cataclysm around the end of the last Ice Age caused a shift in the Earth's crust. The resulting location and orientation of Stonehenge set in stone, quite literally, the direction of all subsequent research and theory. But how likely is it that the site could align on anything by chance? Well, now you can find out with this little demonstration ...

Each time the computer generates a random angle and compares it against the rising and setting of the Sun or Moon at over 20 events, choosing the nearest. Too far means it is worse than the current alignment of Stonehenge towards the summer solstice. Close enough means there's reason to slaughter a pig! It should be noted that the orientation (or azimuth) indicates the position of the Sun as it appears (or disappears) over the horizon and the displacement is simply the angular difference of this to the event. In reality the Sun's elevation (or altitude) above the horizon needs to be taken into consideration, as well as the refraction of the image, local terrain and the true age of the site, all of which have the effect of moving the event several degrees right or left, as is the case with the midsummer sunrise of course.

So, what are the chances of it aligning on the midsummer sunrise? The central axis at Stonhenge is 2º off the midsummer sunrise. It could be 2º off in the opposite direction as well, which means a similar chance alignment would need to be within ±2º or 4/360 = 1 in 90. We must also consider it would be aligned if pointing the other way, halving the odds to 1 in 45. In the above demonstration you should find the chances of landing 'Close Enough' to an event (however insignificant) is 1 in 2. Remember, the Sun and Moon are simply the most easily observed of celestial objects. We could include Venus, Saturn and Sirius, to name a but few other bright objects worthy of so much effort!

But all this is irrelevant. The most important aspect of the design is not what can be seen between the pillars of the Sarsen circle or across any two uprights for that matter - in every case it is the placing of the lintels atop the pillars, those of the Sarsen Circle having been placed absolutely level 4m (13ft) above the ground which is on a slope, and those of the so-called Trilithons placed at such a height that the view of the lintel ring from the central Trilithon is not obstructed.