MILESTONES IN ASTRONOMY

Submitted by: Ansh Gupta

Submitted to: Mrs. Anuradha
 Aristarchus of
Samos First Einstein’s Theory
Proposes a of Relativity Blows
Heliocentric (Sun- Astrophysical
Centered) Universe Minds The First Person on First Image of a
the Moon Black Hole
FEW OF THE
BIGGEST
ACHIEVEMENTS 270 BC 1610 1905 1927 1969 1972 2019
IN ASTRONOMY
EVER
Galileo’s The Discovery of Proof of a Black
Discoveries the Big Bang Hole
Change the Way
we Think about the
World
 Aristarchus of Samos First Proposes a Heliocentric (Sun-Centered) Universe

Aristarchus of Samos was a Greek astronomer who first proposed a heliocentric model of the universe in
which the sun, not the earth, was at the center. Although his theory was noted by other thinkers of his time, it
was rejected as implausible, and the geocentric model was retained for 1,700 years afterward.

Astronomy in ancient Greece developed from the work of the Pre-Socratic Philosophers who advanced a non-
theistic view of the universe in their attempt at defining the First Cause of existence. Their inquiries led them
to astronomical speculation in trying to determine the nature, and position, of the Earth. At this time, Earth
was understood as the center of the universe with the Sun, Moon, and planets revolving around it. Philolaus of
Croton, a Pythagorean philosopher, rejected this model and proposed a Pyro centric view in which the Earth,
and all other planets, revolved around a Central Fire.

Philolaus’ views were rejected, most notably by Aristotle, but may have suggested the heliocentric model to
Aristarchus. Aristarchus’ works are no longer extant save for his On the Sizes and Distances of the Sun and
Moon, but his heliocentric model was preserved by the later mathematician and engineer Archimedes of
Syracuse in his work The Sand Reckoner. The model was rejected not because it was considered inadequate in
explaining observable phenomena regarding the stars, Sun and Moon, and the planets but, essentially, because
it challenged the accepted view of the size of the universe and the Earth’s unique position at its center.

The geocentric model, placing Earth at the center of the universe, was advanced by Hipparchus of Nicaea,
considered the greatest astronomer of his day, and continued in use until it was challenged by the work of
Nicolaus Copernicus and then by others. The heliocentric model was not widely accepted until it was
mathematically proven by Sir Isaac Newton and Aristarchus’ conclusions were validated.
 Galileo’s Discoveries Change the Way we Think about the World

Born in 1564, Italian astronomer Galileo Galilei's observations of our solar system and the Milky Way
have revolutionized our understanding of our place in the Universe.

Galileo sparked the birth of modern astronomy with his observations of the Moon, phases of Venus,
moons around Jupiter, sunspots, and the news that seemingly countless individual stars make up the
Milky Way Galaxy. If Galileo were around today, he would surely be amazed at NASA's exploration of
our solar system and beyond.

After learning of the newly invented "spyglass," a device that made far objects appear closer, Galileo
soon figured out how it worked and built his own, improved version. In 1609, using this early version of
the telescope, Galileo became the first person to record observations of the sky made with the help of a
telescope. He soon made his first astronomical discovery.

At the time, most scientists believed that the Moon was a smooth sphere, but Galileo discovered that the
Moon has mountains, pits, and other features, just like the Earth.

When Galileo pointed his telescope at Jupiter, the largest planet in our solar system, he made a startling
discovery. The planet had four "stars" surrounding it. Within days, Galileo figured out that these "stars"
were actually moons in orbit of Jupiter. His discovery challenged common beliefs of his time about the
bodies of our solar system. Continuing Galileo's legacy, modern telescopes and space probes observe the
wonders of Jupiter's many moons.
Galileo turned his gaze toward Venus, the brightest celestial object in the sky - other than
the Sun and the Moon. With his observations of the phases of Venus, Galileo was able to
figure out that the planet orbits the Sun, not the Earth as was the common belief in his
time.

Curious about the Sun, Galileo used his telescope to learn more. Not knowing that
looking at our very own star would damage his eyesight, Galileo pointed his telescope
towards the Sun. He discovered that the sun has sunspots, which appear to be dark in
color.

Galileo's discoveries about the Moon, Jupiter's moons, Venus, and sunspots supported the
idea that the Sun - not the Earth - was the center of the Universe, as was commonly
believed at the time. Galileo's work laid the foundation for today's modern space probes
and telescopes. Happy Birthday Galileo and thanks for all the celestial gifts!

In 1989, Galileo Galilei was memorialized with the launch of a Jupiter-bound space probe
bearing his name. During its 14-year voyage, the Galileo space probe (and its detachable
mini-probe) visited Venus, Earth, the asteroid Gaspra, observed the impact of Comet
Shoemaker-Levy 9 on Jupiter, Jupiter, Europa, Callisto, Io, and Amalthea.

In order to avoid the possible contamination of one of Jupiter's moons, the Galileo space
probe was purposely crashed into Jupiter at the end of its mission in September 2003.
 Einstein’s Theory of Relativity
Albert Einstein's 1905 theory of special relativity is one of the most important papers ever
published in the field of physics. Special relativity is an explanation of how speed affects mass,
time and space. The theory includes a way for the speed of light to define the relationship
between energy and matter — small amounts of mass (m) can be interchangeable with
enormous amounts of energy (E), as defined by the classic equation E = mc2

Special relativity applies to "special" cases — it's mostly used when discussing huge energies,
ultra-fast speeds and astronomical distances, all without the complications of gravity. Einstein
officially added gravity to his theories in 1915, with the publication of his paper on general
relativity.

As an object approaches the speed of light, the object's mass becomes infinite and so does the
energy required to move it. That means it is impossible for any matter to go faster than light
travels. This cosmic speed limit inspires new realms of physics and science fiction, as people
consider travel across vast distances.

Before Einstein, astronomers (for the most part) understood the universe in terms of three laws
of motion presented by Isaac Newton in 1686. These three laws are:
Objects in motion or at rest remain in the same state unless an external force imposes change. This is also known as the concept of inertia.

The force acting on an object is equal to the mass of the object multiplied by its acceleration. In other words, you can calculate how much force it takes to move objects with various
masses at different speeds.

For every action, there is an equal and opposite reaction.

Newton's laws proved valid in nearly every application in physics. They formed the basis for our understanding of mechanics and gravity.

But some things couldn't be explained by Newton's work: For example, light.

To shoehorn the odd behavior of light into Newton's framework for physics scientists in the 1800s supposed that light must be transmitted through some medium, which they called
the "luminiferous ether." That hypothetical ether had to be rigid enough to transfer light waves like a guitar string vibrates with sound, but also completely undetectable in the
movements of planets and stars.

That was a tall order. Researchers set about trying to detect that mysterious ether, hoping to understand it better. In 1887, wrote astrophysicist Ethan Siegal in the Forbes science blog,
Starts With a Bang, physicist Albert A. Michelson and chemist Edward Morley calculated how Earth's motion through the ether affected how the speed of light is measured, and
unexpectedly found that the speed of light is the same no matter what Earth's motion is.

If the speed of light didn't change despite the Earth's movement through the ether, they concluded, there must be no such thing as ether to begin with: Light in space moved through a
vacuum.

That meant it couldn't be explained by classical mechanics. Physics needed a new paradigm.
 The Discovery of the Big Bang
This startling idea first appeared in scientific form in 1931, in a paper by Georges Lemaitre, a Belgian cosmologist and
Catholic priest. The theory, accepted by nearly all astronomers today, was a radical departure from scientific orthodoxy
in the 1930s. Many astronomers at the time were still uncomfortable with the idea that the universe is expanding. That
the entire observable universe of galaxies began with a bang seemed preposterous .

Lemaitre was born in 1894 in Charleroi, Belgium. As a young man he was attracted to both science and theology, but
World War I interrupted his studies (he served as an artillery officer and witnessed the first poison gas attack in
history). After the war, Lemaitre studied theoretical physics, and in 1923 was ordained as an Abbé. The following year,
he pursued his scientific studies with the distinguished English astronomer Arthur Eddington, who regarded him as “a
very brilliant student, wonderfully quick and clear-sighted, and of great mathematical ability.” Lemaitre then went on
to America, where he visited most of the major centers of astronomical research. Later, he received his Ph.D. in physics
from the Massachusetts Institute of Technology .

In 1925, at age 31, Lemaitre accepted a professorship at the Catholic University of Louvain, near Brussels, a position
he retained through World War II (when he was injured in the accidental bombing of his home by U.S. forces). He was
a devoted teacher who enjoyed the company of students, but he preferred to work alone. Lemaitre’s religious interests
remained as important to him as science throughout his life, and he served as President of the Pontifical Academy of
Sciences from 1960 until his death in 1966.

In 1927, Lemaitre published in Belgium a virtually unnoticed paper that provided a compelling solution to the
equations of General Relativity for the case of an expanding universe. His solution had, in fact, already been derived
without his knowledge by the Russian Alexander Friedmann in 1922. But Friedmann was principally interested in the
mathematics of a range of idealized solutions (including expanding and contracting universes) and did not pursue the
possibility that one of them might actually describe the physical universe. In contrast, Lemaitre attacked the problem of
cosmology from a thoroughly physical point of view, and realized that his solution predicted the expansion of the real
universe of galaxies that observations were only then beginning to suggest .
By 1930, other cosmologists, including Eddington, Willem de Sitter, and Einstein, had concluded that the static (non-evolving) models of the universe they had
worked on for many years were unsatisfactory. Furthermore, Edwin Hubble, using the world’s largest telescope at Mt. Wilson in California, had shown that the distant
galaxies all appeared to be receding from us at speeds proportional to their distances. It was at this point that Lemaître drew Eddington’s attention to his earlier work,
in which he had derived and explained the relation between the distance and the recession velocity of galaxies. Eddington at once called the attention of other
cosmologists to Lemaître’s 1927 paper and arranged for the publication of an English translation. Together with Hubble’s observations, Lemaître’s paper convinced
the majority of astronomers that the universe was indeed expanding, and this revolutionized the study of cosmology.

A year later, Lemaître explored the logical consequences of an expanding universe and boldly proposed that it must have originated at a finite point in time. If the
universe is expanding, he reasoned, it was smaller in the past, and extrapolation back in time should lead to an epoch when all the matter in the universe was packed
together in an extremely dense state. Appealing to the new quantum theory of matter, Lemaître argued that the physical universe was initially a single particle—the
“primeval atom” as he called it—which disintegrated in an explosion, giving rise to space and time and the expansion of the universe that continues to this day. This
idea marked the birth of what we now know as Big Bang cosmology.

It is tempting to think that Lemaître’s deeply-held religious beliefs might have led him to the notion of a beginning of time. After all, the Judeo-Christian tradition had
propagated a similar idea for millennia. Yet Lemaître clearly insisted that there was neither a connection nor a conflict between his religion and his science. Rather he
kept them entirely separate, treating them as different, parallel interpretations of the world, both of which he believed with personal conviction. Indeed, when Pope
Pius XII referred to the new theory of the origin of the universe as a scientific validation of the Catholic faith, Lemaître was rather alarmed. Delicately, for that was his
way, he tried to separate the two:

“As far as I can see, such a theory remains entirely outside any metaphysical or religious question. It leaves the materialist free to deny any transcendental Being…
For the believer, it removes any attempt at familiarity with God… It is consonant with Isaiah speaking of the hidden God, hidden even in the beginning of the
universe.”

In the latter part of his life, Lemaître turned his attention to other areas of astronomical research, including pioneering work in electronic computation for
astrophysical problems. His idea that the universe had an explosive birth was developed much further by other cosmologists, including George Gamow, to become the
modern Big Bang theory. While contemporary views of the early universe differ in many respects from Lemaître’s “primordial atom,” his work had nevertheless
opened the way. Shortly before his death, Lemaître learned that Arno Penzias and Robert Wilson had discovered the cosmic microwave background radiation, the first
and still most important observational evidence in support of the Big Bang.
 The First Person on the Moon
Neil Alden Armstrong (August 5, 1930 – August 25, 2012) was an American astronaut and aeronautical engineer who in 1969 became the first person to walk on the Moon. He was also a naval
aviator, test pilot, and university professor.

Armstrong was born and raised in Wapakoneta, Ohio. He entered Purdue University, studying aeronautical engineering, with the U.S. Navy paying his tuition under the Holloway Plan. He became
a midshipman in 1949 and a naval aviator the following year. He saw action in the Korean War, flying the Grumman F9F Panther from the aircraft carrier USS Essex. After the war, he completed
his bachelor's degree at Purdue and became a test pilot at the National Advisory Committee for Aeronautics (NACA) High-Speed Flight Station at Edwards Air Force Base in California. He was the
project pilot on Century Series fighters and flew the North American X-15 seven times. He was also a participant in the U.S. Air Force's Man in Space Soonest and X-20 Dyna-Soar human
spaceflight programs.

Armstrong joined the NASA Astronaut Corps in the second group, which was selected in 1962. He made his first spaceflight as command pilot of Gemini 8 in March 1966, becoming NASA's first
civilian astronaut to fly in space. During this mission with pilot David Scott, he performed the first docking of two spacecraft; the mission was aborted after Armstrong used some of his re-entry
control fuel to stabilize a dangerous roll caused by a stuck thruster. During training for Armstrong's second and last spaceflight as commander of Apollo 11, he had to eject from the Lunar Landing
Research Vehicle moments before a crash.

On July 20, 1969, Armstrong and Apollo 11 Lunar Module (LM) pilot Buzz Aldrin became the first people to land on the Moon, and the next day they spent two and a half hours outside the Lunar
Module Eagle spacecraft while Michael Collins remained in lunar orbit in the Apollo Command Module Columbia. When Armstrong first stepped onto the lunar surface, he famously said: "That's
one small step for man, one giant leap for mankind.” It was broadcast live to an estimated 530 million viewers worldwide. Apollo 11 was a major U.S. victory in the Space Race, by fulfilling a
national goal proposed in 1961 by President John F. Kennedy "of landing a man on the Moon and returning him safely to the Earth" before the end of the decade. Along with Collins and Aldrin,
Armstrong was awarded the Presidential Medal of Freedom by President Richard Nixon and received the 1969 Collier Trophy. President Jimmy Carter presented him with the Congressional Space
Medal of Honor in 1978, he was inducted into the National Aviation Hall of Fame in 1979, and with his former crewmates received the Congressional Gold Medal in 2009.

After he resigned from NASA in 1971, Armstrong taught in the Department of Aerospace Engineering at the University of Cincinnati until 1979. He served on the Apollo 13 accident investigation
and on the Rogers Commission, which investigated the Space Shuttle Challenger disaster. In 2012, Armstrong died due to complications resulting from coronary bypass surgery, at the age of 82.
 Proof of the black hole
Black holes are among the most mysterious and fascinating features of the universe, captivating scientists since
the 18th century, including Albert Einstein and Stephen Hawking.

They are often described as consuming their surrounding gas, the result of gravity so intense that nothing can
escape its pull, not even the fastest known traveler in the universe: light itself. But if black holes don’t emit or
reflect light, which means we can’t see them, how do astronomers know they are there?

The answer actually applies to many subjects studied in physics and deep-space astronomy—when you can’t
observe something directly, or you can’t explain something you are seeing, you make educated guesses based on
what you do see: the effect on other objects. On Earth, you can know it’s a windy day without stepping outside,
because a flag is flapping. Astronomers know there is a black hole when the stars or gas around it are distorted
or otherwise changed. These effects show up in a few ways.
Astronomers can observe a star accelerating in orbit around an unseen companion, rather than a detectable
binary companion star. By measuring the orbiting star’s rate of acceleration, astronomers can calculate the mass
of the object pulling on it; when this mass is so large that nothing else can explain it, astronomers conclude it is
a black hole.
The answer actually applies to many subjects studied in physics and deep-space astronomy—when you can’t
observe something directly, or you can’t explain something you are seeing, you make educated guesses based on
what you do see: the effect on other objects. On Earth, you can know it’s a windy day without stepping outside,
because a flag is flapping. Astronomers know there is a black hole when the stars or gas around it are distorted
or otherwise changed. These effects show up in a few ways.
Astronomers can observe a star accelerating in orbit around an unseen companion, rather than a detectable
binary companion star. By measuring the orbiting star’s rate of acceleration, astronomers can calculate the mass
of the object pulling on it; when this mass is so large that nothing else can explain it, astronomers conclude it is
a black hole
 First Image of a Black Hole
The supermassive
black hole imaged
Using the Event by the EHT is
Horizon located in the
Telescope, center of the
scientists elliptical galaxy
obtained an M87, located
image of the about 55 million
black hole at light years from
Earth. This image
the center of the was captured by
galaxy M87. FORS2 on ESO's
(There is a Very Large
supermassive Telescope. The
black hole at short linear
the center of feature near the
our galaxy — center of the
image is a jet
the Milky Way.) produced by the
black hole.