Changing understanding

Ever since prehistory human beings have been trying to record and predict the movement of celestial bodies.
Indigenous cultures around the world have long performed astronomical observation with the naked eye, using them for navigation, timekeeping, agricultural planning, spiritual and religious practices. Many star charts have been discovered, which reveal clear efforts to map the night sky and learn more about the mechanics of our universe. As early as the 6th century BCE, ancient Greek philosophers documented evidence that Earth was a sphere. They noted that the night sky looked different when seen from various locations on Earth, hinting at the planet's curved surface. They also observed the round shadow of Earth on the Moon during lunar eclipses. These philosophers were even able to calculate the circumference of Earth quite accurately. In the year 185, Chinese astronomers became the first to document a supernova.
Before the 16th century, Earth was commonly thought to be at the centre of the solar system, with all other celestial objects revolving around it. This is known as the geocentric model. This theory, however, did not match observations made by astronomers, such as the path of planets that appeared to move backwards in their orbits. In 1543, Polish astronomer Nicolaus Copernicus proposed a heliocentric model of the solar system in which the planets orbit the Sun. This model explained the unusual path of planets that astronomers had observed. The new theory was one of many revolutionary ideas about astronomy that emerged during the Renaissance period.
These works faced opposition from the catholic church, as they violated the holy scriptures, which placed the Earth in the middle of the Universe.
The work of astronomers Tycho Brahe and Johannes Kepler led to an accurate description of planetary motions and laid the foundation for Isaac Newton's theory of gravitation. This progress dramatically improved humanity's understanding of the universe. Their observations and investigations were strengthened by the invention of the telescope in the early 17th century. Italian astronomer Galileo Galilei popularized the use of telescopes to study and discover celestial objects, including Jupiter's four biggest moons. In his honour, they are known as the Galilean moons.

Astronomers of the past

Ptolemy (c. 100 AD - c. 170 AD) lived in the city of Alexandria under the rule of he Roma Empire. By incorporating numerous epicycles rotating at varying speeds, he developed an astronomical model whcih allowed one to predict future positions of celestial bodies, as well as eclipses of the Sun and Moon. Ptolemy also assembled a star catalogue, with a list of 48 cansetellations. His model, however, was, as those created before him, geocentric, with the Earth sitting motionless in the centre of the Universe and other celestial bodies attached to giant rotating spheres, and it would remain so until the scientific revolution hundreds of years later.

Nicolaus Copernicus (1473 – 1543) was born in Royal Prussia. Copernicus developed the first heliocentric model with planets, including Earth, revolving around the rigid Sun. Beides orbiting the Sun, in his the Earth also turned once daily on its own axis. This model, while closer to our modern perception of the world, too had its flaws. Copernicus saw the Sun as the centre of the entire Universe, not just the Solar system. In his view, the orbits of planets remained perfectly circular, not elliptical, which forced him to incorporate numerous epicycles like in Ptolemy's model. With no concept of gravity, Earth and the planets still revolved around the sun on giant transparent spheres.

Galileo Galilei (1564-1642) was born in Italy. Galileo’s laws of motion, derived from his measurements that all bodies accelerate at the same rate regardless of their mass or size, paved the way for the development of classical mechanics by Newton. Galileo’s heliocentrism (with modifications by Kepler) soon became accepted scientific fact. His inventions, from compasses and balances to improved telescopes and microscopes, revolutionized astronomy and biology. Galileo discovered craters and mountains on the moon, the phases of Venus, Jupiter’s moons and the stars of the Milky Way.
In 1633, Galileo was put on trial by the Inquisiton, convicted of “vehement suspicion of heresy”, and forced to denounce his works.

Johannes Kepler (1571 - 1630) was born in Germany. Kepler discovered 3 major laws of planetary motion:
1) the planets move in elliptical orbits with the Sun at one focus;
2) the time necessary to travel any arc of a planetary orbit is proportional to the area of the sector between the central body and that arc;
3) there is an exact relationship between the squares of the planets’ periodic times and the cubes of the radii of their orbits.
These laws directly influenced Newton when deriving his general physical principles.

Key inventions

Before the Telescope

Astrolabes, which could locate and predict the movement of heavenly bodies like the Moon, planets, and stars, were first developed in the 11th century BC. They were used for telling time, and predicting and charting the movement of stars and planets.

People created star maps to better understand the havens and their organizations. Stars were grouped into constellations and categorized by their apparent brightness.

Prior to the development of reliable clocks, sundials, which tell the time of day by the position of the Sun, were used insted. Stars other than the Sun could also be used in similar dials.

The Telescope

In 1608 in the Netherlands, a patent for the 1st telescope was submitted by Hans Lippershey, an eyeglass maker. News of the invention soon spread across Europe. The design of these early refracting telescopes consisted of a convex objective lens and a concave eyepiece. Galileo improved on this design the following year and applied it to astronomy. In 1611, Kepler described how a far more useful telescope could be made with a convex objective lens and a convex eyepiece lens.
A common problem with early refracting telescopes was the chromatic and spherical abberations (defects in images produced to the inability of the len to focus all wave lengths of light in one point). Inventors sought ways to liquidate these effects. Newton is credited with building the 1st functional reflecting telescope in 1668 with a small flat diagonal mirror to reflect the light to an eyepiece placed on the side of the telescope.
In 1666, Newton discovered that chromatic colors arose from the uneven refraction of light as it passed through the glass medium. In 1733, an inventor by the name Chester Moore Hall was able to construct the 1st achromatic telescope by combining lenses made from different types of glass (each with a different refractive index).
In the 19th century, glass reflective telescope mirrors began to be covered in a layer of silver, which is much more reflective than speculum mirrors.

The first telescope was constructed in 1608.

Chromatic aberration occur when the lens is unable to focus all wave lengths of light in one point.

The image therefore appears distorted.

The first reflecting telescope was developed by Isaac Newton in 1668.

Refracting vs Reflecting telescope