I.
stars from the Earth
There are basically 3 types of telescopes:
– lens telescopes, refractors (Sir Isaac Newton)
– mirror telescopes, reflectors (Lauren Cassegrain)
– telescopes containing both a lens and a mirror, catadioptric (Bernard Schmidt)
No, the following description will not be focused on the types, especially since there are so many different types of telescopes. Let’s take a look at how we got to these basic types and what changed when we raised these wonders to the sky while still here on Earth. More…
The lenses of glasses, which already existed in the 14th century, gave the idea for the first telescope. But before that, a little telescope world history.
The Heliocentric model (heliocentrism) actually begins with him. Ancient Greek (lived approximately 310 BC – 230 BC) philosopher, mathematician, astronomer. He was the first to think that the SUN was the center of the Universe and that everything revolved around it. Before our era… But with his death, unfortunately, his assumption, which was very inconsistent with the worldview and culture of the time, was easily forgotten.
Ptolemy –
A Egyptian astronomer, mathematician, geographer, and poet who lived between about 85 and 168 AD. The Geocentric model he developed, according to which the Earth is the center around which the planets and stars revolve, persisted until the 17th century. His assumption was also that the Earth has a regular, spherical shape.
Polish astronomer (February 19, 1473 – May 24, 1543), known developer of the Heliocentric worldview. Everything revolves around the Sun, the MOON revolves around the Earth, and the Earth rotates around its own axis. He published about this, but at that time his discovery did not yet receive the same outrage from the church as in Galileo’s time, because his publisher presented his work as a hypothesis.
Let’s get started! =)
The Beginnings
Let’s just say that the telescope originated in the Netherlands. From there, it spread worldwide and reached the Italian astronomer, physicist, mathematician, and naturalist Galileo Galilei (February 15, 1564 – January 8, 1642), who saw further potential in the subject. The history of telescopic astronomy begins with him, when he built his own telescope (with a convex and a concave lens), with which he began to observe the sky. In 1610, he published his book Sidereus Nuncius (Astrological Messenger) about his observations.
He discovered the 4 moons of Jupiter, and he was the first to notice the rings of Saturn, as well as the craters and mountains of the Moon. It was then that he realized that the surfaces of the planets are uneven and their shapes are not perfect spheres. He also observed Neptune, but did not attach much importance to it, not knowing that it was a planet. He was the one who realized that the Milky Way was a multitude of stars, and he identified many stars. He observed Venus and, based on its changing phases, determined that it revolves around the Sun. He was the first European to see sunspots, from the movement of which he determined that the Sun also rotates. All his observations supported the heliocentric worldview. Later, he went to Rome to tell the church about the Copernican system, which ended in his being forced to remain silent. A few years later, his friend Cardinal Barberini became pope and published a book on the Copernican system. This resulted in an Inquisition trial and a plea bargain. Galileo admitted his error, his works were banned, and he spent the rest of his life under house arrest.
Galileo presented his telescope in Venice in 1609, and it was a great success among shipping merchants. In 1611, this telescope was further improved by Johannes Kepler (December 27, 1571 – November 15, 1630) (it used two convex lenses), which made it much more focused.
For a long time, no major breakthrough was made despite continuous experimentation. However, the lenses were defective (chromatic aberration, for example), and long-focus telescopes were not a solution, because these telescopes were more than 10 meters long.
The development
In 1668, Sir Isaac Newton (December 25, 1642 – March 20, 1727) an English physicist, mathematician, astronomer, philosopher and alchemist created the reflecting telescope, which managed to eliminate chromatic aberration. One mirror projects the image onto another, which projects it further into the eyepiece (which we look into).
In 1672, the invention of the French scientist and priest Laurent Cassegrain (c. 1629 – August 31, 1693) was introduced, who made it possible to extend the focal length with a convex auxiliary mirror.
In the 1720s, Chester Moore Hall (December 9, 1703 – March 17, 1771) a British inventor and lawyer created the achromatic lens. This is a combination of 2 types of glass, which gives a clear image, and the telescope (tube) could be shorter.
Sir Frederick William Herschel (November 15, 1738 – August 25, 1822) was a German-English composer and astronomer who discovered Uranus, its two moons, and two more moons of Saturn with a huge telescope he built himself. Technically, his telescopes did not have auxiliary mirrors. The diameter of the telescope he made – and the largest of his time – was 126 centimeters. He determined that the light from the Sun also radiates heat beyond the visible color range (a little help here), or the existence of infrared radiation.
Newton made the mirror for the telescope from a metal alloy, but its light was not durable, and it did not regain its original shine even after re-polishing. Around 1850, it was discovered that glass was also suitable as a mirror, coated with silver.
When photography was invented (1839), attempts were made to record the images shown by telescopes. Henry Draper (March 7, 1837 – November 20, 1882) was an American physician and astronomer who was one of the pioneers of astrophotography. He demonstrated that stars and planets could be captured using long exposures.
The Baltic optician Bernhard Woldemar Schmidt (March 30, 1879 – December 1, 1935) invented a correction plate that eliminates spherical distortion. This is primarily used for astrophotography.
The big jump
George Ellery Hale (June 29, 1868 – February 21, 1938) was an American solar astronomer who realized that we could discover more of the Universe with large reflecting mirrors. He is credited with the most powerful telescopes of his time, such as the 100-inch (2.5-meter) Hooker Telescope.
Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer who discovered spiral galaxies with the largest and best telescope at the time, and that they were not part of the Milky Way, but separate galaxies. This telescope was the Hooker Telescope (you can still look inside it today, even all night long, if you make an appointment and have a thick wallet: Mount Wilson Observatory). The other discovery related to it: the expanding universe. This was actually established a long time ago, but it was widely explained and clarified by him (Hubble’s law), according to which: the distance between galaxies is directly proportional to the speed of the distance. How far a galaxy or a star is moving away from another and how fast, can be determined from the light they emit (redshift).
Astronomers use a prism to break up the light of a star. This color scale is the spectrum. With the development of technology, from the 1950s onwards, they began to record the light electronically and study the colors in even more detail. Based on the spectra, for example, we can determine what materials the star is made of, what its external temperature is, etc.
Telescopes with increasingly larger mirrors were made, but the weight of the glass was always a problem. New manufacturing techniques were born in the 1980s: honeycomb structure (not a solid surface mirror, which was developed by Roger Angel (February 7, 1941 – ) and John Hill), and the mirror consisting of separate segments (yes, like the James Webb Space Telescope).
One of the biggest launches from here on Earth is the Large Synoptic Survey Telescope, or LSST. This is a panoramic telescope, it scan and record the ENTIRE sky. The diameter of the primary mirror is: 8.4 meters.
The other is the Advanced Technology Solar Telescope, or ATST, or Inouye Solar Telescope. The primary mirror is 4 meters, currently the largest solar telescope in the world. It is used to examine the surface of the Sun, its atmosphere, solar flares, and solar wind.
Active and adaptive optics
The atmosphere can distort the image of the observed object. They try to compensate for this by, for example, moving the auxiliary mirror and deforming the main mirror. If there is no bright star in the field of view, for example, they illuminate the sky with laser light (sodium atoms reflect the yellowish white light). This is the reference starlight.
Interferometry
The resolution of the telescope’s images is increased by examining the same object with several telescopes at the same time.
Radio telescopes
Mostly parabolic antennas. The larger the antenna, the better it amplifies the signals. The first such radiation was detected from the Milky Way by chance. The Bell Telephone Company searched for radio signals that could interfere with radio transmissions. Radio waves fall outside the visible range. This is how pulsars (a type of neutron star that is usually created after a supernova explosion) and quasars were discovered.
SETI is also a radio telescope: Search for Extra-Terrestrial Intelligence. Its purpose is in its name. =)
It’s not over yet
Telescopes are built, and have been built, as high as possible, in places with cleaner, drier air, and no light pollution. However, Newton already knew that the Earth’s atmosphere interferes. Even so… In order to get an even clearer picture of what’s out there, we need to look above the atmosphere.
We need a space telescope.
This concludes our quick telescopic exploration from Earth. In the next chapter: we’ll head to Space with the first space telescope, which is none other than: Hubble. =)
Be a Nerdy Bird!
[…] Telescopes are built, and have been built, as high as possible, in places with cleaner, drier air, and no light pollution. However, Newton already knew that the Earth’s atmosphere interferes. Even so… In order to get an even clearer picture of what’s out there, we need to look above the atmosphere. We need a space telescope. This concludes our quick telescopic exploration from Earth. In the next chapter: we’ll head to Space with the first space telescope, which is none other than: Hubble. =) – GLASSES TO TELESCOPE […]