The Milky Way - PowerPoint Presentation

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The Milky WaySlide2

The Greek philosopher Democritus (450–370 BC) proposed that the bright band on the night sky known as the Milky Way might consist of distant stars. Aristotle (384–322 BC), however, believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which is continuous with the heavenly motions.“ The

Neoplatonist

philosopher

Olympiodorus

the Younger (c. 495–570 AD) criticized this view, arguing that if the Milky Way were sublunary it should appear different at different times and places on the Earth, and that it should have parallax, which it does not. In his view, the Milky Way was celestial. This idea would be influential later in the Islamic world.Slide3

According to

Mohaini

Mohamed, the Arabian astronomer,

Alhazen

(965–1037), made the first attempt at observing and measuring the Milky Way's parallax, and he thus "determined that because the Milky Way had no parallax, it was very remote from the Earth and did not belong to the atmosphere.“ An Persian astronomer proposed the Milky Way galaxy to be "a collection of countless fragments of the nature of nebulous stars.“ An

Andalusian

astronomer proposed that the Milky Way was made up of many stars that almost touch one another and appear to be a continuous image due to the effect of refraction from sublunary material, citing his observation of the conjunction of Jupiter and Mars as evidence of this occurring when two objects are near. In the 14th century, a Syrian-born scientist proposed the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars".Slide4

The Proof

Actual proof of the Milky Way consisting of many stars came in 1610 when Galileo

Galilei

used a telescope to study the Milky Way and discovered that it is composed of a huge number of faint stars. In 1750 Thomas Wright, in his An original theory or new hypothesis of the Universe, speculated (correctly) that the galaxy might be a rotating body of a huge number of stars held together by gravitational forces, akin to the solar system but on a much larger scale. The resulting disk of stars can be seen as a band on the sky from our perspective inside the disk. In a essay in 1755, Immanuel Kant elaborated on Wright's idea about the structure of the Milky Way.Slide5

The first attempt to describe the shape of the Milky Way and the position of the Sun in it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the solar system close to the center. Using a refined approach,

Kapteyn

in 1920 arrived at the picture of a small (diameter about 15

kiloparsecs

) ellipsoid galaxy with the Sun close to the center. Slide6

A different method by Harlow Shapley based on the cataloguing of globular clusters led to a radically different picture: a flat disk with diameter approximately 70

kiloparsecs

and the Sun far from the center. Both analyses failed to take into account the absorption of light by interstellar dust present in the galactic plane, but after Robert Julius

Trumpler

quantified this effect in 1930 by studying open clusters, the present picture of our galaxy, the Milky Way, emerged.Slide7

The shape of the Milky Way as deduced from star counts by William Herschel in 1785; the solar system was assumed to be near the center.Slide8

Solar SystemSlide9

The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass (well over 99%) is in the sun. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets whose orbits are almost circular and lie within a nearly flat disc called the ecliptic plane. Slide10

PLANETS

The four smaller inner planets, Mercury,

V

enus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, the gas giants, are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn -, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely

largely

of ices, such as water, ammonia and methane, and are often referred to separately as "ice giants".Slide11

The Solar System is also home to a number of regions populated by smaller objects. The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc; linked populations of trans-Neptunian objects composed mostly of ices such as water, ammonia and methane. Within these populations, five individual objects, Ceres, Pluto,

Haumea

,

Makemake

and Eris, are recognized to be large enough to have been rounded by their own gravity, and are thus termed dwarf planets. In addition to thousands of small bodies in those two regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.Slide12
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Six of the planets and three of the dwarf planets are orbited by natural satellites,[b] usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles.

The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the

heliosphere

, which extends out to the edge of the scattered disc. The hypothetical

Oort

cloud, which acts as the source for long-period comets, may also exist at a distance roughly a thousand times further than the

heliosphere

.

The Solar System is located in the Milky Way galaxy, which contains about 200 billion stars.Slide17

Our Solar SystemSlide18

Discovery and Exploration

For many thousands of years, humanity, with a few notable exceptions, did not recognize the existence of the Solar System. People believed the Earth to be stationary at the center of the universe and categorically different from the divine or ethereal objects that moved through the sky. Although the Greek philosopher Aristarchus of Samos had speculated on a heliocentric reordering of the cosmos,

Nicolaus

Copernicus was the first to develop a mathematically predictive heliocentric system.Slide19

His 17th-century successors, Galileo

Galilei

, Johannes

Kepler

and Isaac Newton, developed an understanding of physics that led to the gradual acceptance of the idea that the Earth moves around the Sun and that the planets are governed by the same physical laws that governed the Earth. Additionally, the invention of the telescope led to the discovery of further planets and moons. In more recent times, improvements in the telescope and the use of unmanned spacecraft have enabled the investigation of geological phenomena such as mountains and craters, and seasonal meteorological phenomena such as clouds, dust storms and ice caps on the other planets.Slide20

Structure

The principal component of the Solar System is the Sun, a main-sequence G2 star that contains 99.86 percent of the system's known mass and dominates it gravitationally.[3] The Sun's four largest orbiting bodies, the gas giants, account for 99 percent of the remaining mass, with Jupiter and Saturn together comprising more than 90 percent.Slide21

Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are frequently at significantly greater angles to it. All the planets and most other objects orbit the Sun in the same direction that the Sun is rotating (counter-clockwise, as viewed from above the Sun's north pole). There are exceptions, such as Halley's Comet.Slide22

How long does it take the sun to reach objects in our solar system?

Mercury

~ 3.16 minutes (190 seconds)

Venus

~ 6 minutes (360 seconds)

Earth

~ 8.3333 minutes (500 seconds)

Moon: Approximately the same as Earth

Mars

~ 12.6 minutes (760 seconds)

Jupiter

~ 43 minutes

Saturn

~ 1 hour 20 minutes

Uranus

~ 2 hours 40 minutes

Neptune

~ 4 hours 40 minutes

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Dwarf Planets

Pluto

~ 5 hours 30 minutes

Ceres

~ 23 minutes

Eris

~ 9 hours 23 minutesSlide23
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Comet Hale-Bopp

March 3, 1997Slide26

Comet PANSTARRS March 2, 2013Slide27

Comet ISON November – December 2013

Prospective ViewSlide28
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The overall structure of the charted regions of the Solar System consists of the Sun, four relatively small inner planets surrounded by a belt of rocky asteroids, and four gas giants surrounded by the outer Kuiper belt of icy objects. Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the asteroid belt. The outer Solar System is beyond the asteroids, including the four gas giant planets. Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune.Slide30

Kepler's

laws of planetary motion describe the orbits of objects about the Sun. Following

Kepler's

laws, each object travels along an ellipse with the Sun at one focus. Objects closer to the Sun (with smaller semi-major axes) travel more quickly, as they are more affected by the Sun's gravity. On an elliptical orbit, a body's distance from the Sun varies over the course of its year. A body's closest approach to the Sun is called its perihelion, while its most distant point from the Sun is called its aphelion. The orbits of the planets are nearly circular, but many comets, asteroids and Kuiper belt objects follow highly elliptical orbits.Slide31

Due to the vast distances involved, many representations of the Solar System show orbits the same distance apart. In reality, with a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between it and the previous orbit. Attempts have been made to determine a relationship between these orbital distances but no such theory has been accepted.Slide32

Most of the planets in the Solar System possess secondary systems of their own, being orbited by planetary objects called natural satellites, or moons (two of which are larger than the planet Mercury), or, in the case of the four gas giants, by planetary rings; thin bands of tiny particles that orbit them in unison. Most of the largest natural satellites are in synchronous rotation, with one face permanently turned toward their parent.