The biology of the eye is extremely complex, especially when you consider the human eye only has the rough diameter of 2.54 cm and weighs approximately 7.5 grams. It is made up of around 15 distinct parts, all with different roles to play in receiving light into the eye and transmitting the electrical impulses, which ultimately relay image information to our brains so that we can perceive the world we live in.

The eye is often compared to a basic camera, and indeed the very ﬁrst camera was designed with the concept of the eye in mind. We can reduce the complex process that occurs to process light into vision within the eye to a relatively basic sequence of events. First, light passes through the cornea, which refracts the light so that it enters the eye in the right direction, and aqueous humour, into the main body of the eye through the pupil. The iris contracts to control pupil size and this limits the amount of light that is let through into the eye so that light-sensitive parts of the eye are not damaged.

The pupil can vary in size between 2 mm and 8 mm, increasing to allow up to 30 times more light in than the minimum. The light is then passed through the lens, which further refracts the light, which then travels through the vitreous humour to the back of the eye and is reﬂected onto the retina, the centre point of which is the macula.

The retina is where the rods and cones are situated, rods being responsible for vision when low levels of light are present and cones being responsible for colour vision and speciﬁc detail. Rods are far more numerous as more cells are needed to react in low levels of light and are situated around the focal point of cones. This focal gathering of cones is collectively called the fovea, which is situated within the macula. All the light information that has been received by the eye is then converted into electrical impulses by a chemical in the retina called rhodopsin, also known as purple visual, and the impulses are then transmitted through the optic nerve to the brain where they are perceived as ‘vision’. The eye moves to allow a range of vision of approximately 180 degrees and to do this it has four primary muscles which control the movement of the eyeball. These allow the eye to move up and down and across, while restricting movement so that the eye does not rotate back into the socket.

Look inside the human eye

An eye-opening look into how vision and sight works.

To date there have been 42 missions to Mars, with exactly half of them complete failures. Other than the Earth it is the most studied planet in the solar system, and for centuries it has been at the heart of wild speculation and groundbreaking scientiﬁc discoveries. Observations of Mars have not only revealed otherwise unknown secrets but also posed new and exciting questions, and it is for these reasons that it has become the most intriguing planetary body of our time. Take a look at the map above to see key geological points of interest as well as the landing and crash sites for several spacecraft.

This image of the surface of Mars was created by reconstructing data from NASA’s Mars Global Surveyor, the Mars Orbiter Laser Altimeter and observations by NASA’s Viking spacecraft.

The surface of Mars

Take a virtual stroll around the Red Planet.

Rockets like Saturn V, the one used to launch NASA’s Apollo and Skylab programs, are multi-stage liquid-fuelled boosters. The Saturn V is considered to be the biggest, most powerful and most successful rocket ever built.

The Saturn V was 110.6m tall, 10.1m in diameter and had a payload of 119,000kgs to low-Earth orbit.

There were three stages, followed by an instrument unit and the payload (spacecraft). The total mission time for this rocket was about 20 mins. The centre engine was ignited first, then engines on either side ignited. The first stage lifted the rocket to about 70m and burned for 2.5 mins.

When sensors in the tanks sensed that the propellant was low, motors detached the first stage. The second stage continued the trajectory to 176km and burned for six mins. About halfway through this stage’s ignition, the instrument unit took control of calculating the trajectory.

Second stage complete, solid-fuel rockets fired it away from the third stage. The third stage burned for 2.5 mins and stayed attached to the spacecraft while it orbited the Earth, at an altitude of 191.2km.

It continued to thrust and vent hydrogen before ramping up and burning for six more minutes, so the spacecraft could reach a high enough velocity to escape Earth’s gravity.

See inside the Saturn V rocket

This illustrated cutaway of the Saturn V shows the 110m high rocket and its 3 stages in amazing detail with full notes

Widely considered by academics to be one of the most influential inventions of the past 1,000 years, the printing press set in motion both the democratisation of knowledge and the establishment of our modern, knowledge-based economies.

For the first time, valued texts could be produced in their thousands and – thanks to the co-evolution of nationwide and international trade routes – allowed texts to be accessed widely by the majority, not just the wealthy aristocracy and intellectual elite.

The man credited with the invention of the printing press is inventor Johannes Gutenberg, who lived and invented the press in Mainz, Germany. Here, around the year 1440 – an exact date is not known – Gutenberg designed a device based on screw presses that, when partnered with inked movable type heads, allowed paper to be quickly and efficiently pressed with letters.

The type heads were made by pouring a lead-tin alloy into a hand mould, and were then affixed to the top of movable, rectangular stalks. The stalks could then be arranged in order to create words and sentences within a rectangular container, before being fed under a screw press. The screw press then clamped a paper sheet on top of the type heads, pressing their ink onto the sheet.

While sounding crude by modern standards, in the 15th Century this was a groundbreaking invention. Before the Gutenberg press, texts were largely hand copied by monks and select few learned individuals. As such, the availability and cost of these texts was immense and they could only be accessed by a minuscule percentage of people.

Consequently, by the mid 16th Century and on to the Renaissance, printing presses had exploded all over Western Europe, producing millions of mass-produced texts on a diverse array of topics from politics to botany. Indeed, famous English philosopher Francis Bacon said that the emergence of typographical printing had “changed the whole face and state of things throughout the world.”

See inside the Gutenberg printing press

This exploded diagram of the Gutenberg printing press gives you a glimpse inside one of the most influential inventions of the past 1,000 years

Designed in the aftermath of the evacuation of Dunkirk by the British Expeditionary Force, the Churchill tank was Britain’s attempt to readdress the technology gap between their ageing Matilda II battalion and the German Panzer tanks that had them out- gunned.

The result was the Mark I, a heavily armoured battle tank equipped with a two- pounder main gun, three-inch howitzer in the rear and the most advanced and robust suspension system yet conceived. It was a defensive juggernaut, designed with one goal: to dominate the European theatre of war.

From its introduction in June 1941, the tank proved a reliable and versatile weapon platform capable of engaging targets quickly and efficiently. Key to this was its high speed of 26km/h (16mph) and excellent turning ability, characteristics made possible by its multiple-bogie suspension system. The suspension was fitted to the hull under two large pannier enclosures on either side, with the tracks running over the top.

Initially, the Churchill was fitted with a two- pounder main gun and three-inch howitzer (artillery piece); however, the former was soon upgraded to a six-pounder cannon and the latter replaced with a high-calibre machine gun.

These cannons gave the Churchill decent stopping power against medium armour, yet still left them short in firepower when compared with their German contemporaries. The Churchill’s main cannon continued to be improved throughout its lifespan, with 75mm guns fitted to Mk IIIs.

Despite its average firepower, however, the Churchill’s high manoeuvrability and excellent armour made it one of the foremost tanks of WWII, being extensively deployed in Europe and North Africa.

See inside a Churchill Mk VII tank

Check out our illustrated guide to one of the most successful Churchill variants of World War II to discover what made it so ruthless, reliable and iconic

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