The scientific study of matter in outer space, especially the positions, dimensions, distribution, motion, composition, energy, and evolution of celestial bodies and phenomena.
Introduction to some basic knowledge:
SCIENCE: KEY TO COMPREHENDING THE COSMOS
The ancient Greeks laid the groundwork for progress in science. Early Greek astronomers devised a Geocentric cosmology, which placed the Earth at the centre of the universe.
The scientific method is a procedure for formulating theories that correctly predict how the universe behaves.
A scientific theory must be testable, that is, capable of being disproved.
Theories are tested and verified by observation or experimentation and result in a process that often leads to their refinement or replacement and to the progress of science.
Observations of the cosmos have led astronomers to discover some fundamental physical laws of the universe.
ORIGINS OF THE SUN-CENTRED UNIVERSE
Copernicus's heliocentric theory simplified the general explanation of planetary motions compared to the geocentric theory.
In a heliocentric cosmology, the Earth is but one of several planets that orbit the Sun.
Geocentric model
FORMATION OF THE SOLAR SYSTEM:
Hydrogen, helium, and traces of lithium, the three lightest elements, were formed shortly after the creation of the universe. The heavier elements were produced much later by stars and cast into space when the stars died. By mass, 98% of the matter in the universe is hydrogen and helium.
The solar system formed 4.6 billion years ago from a swirling, disk-shaped cloud of gas, ice and dust called the solar nebula.
The four inner planets formed through the accretion of dust particles into planetesimals and then into larger protoplanets. The four large outer planets probably formed through the run away accretion of gas and ice onto rocky protoplanetarty cores.
The Sun formed at the centre of the solar nebula. After about one hundred million years, the temperature at the protosun's centre was high enough to ignite thermo macular reactions. For 800 million years after the Sun formed, impact of asteriod-like objects on the young planets dominated the history of the solar system.
COMPARATIVE PLANETOLOGY
The four inner planets of the solar system share many characteristics and are distinctly different from the four giant outer planets.
The four inner, terrestrial planets are relatively small, have high average densities, and are composed primarily of rock and metal.
Jupiter and Saturn have large diameters and low densities and are composed primarily of hydrogen and helium. Uranus and Neptune have large quantities of water as well as much hydrogen and helium.
Asteroids are rocky and metallic debris in the solar system larger than about a kilometer in diameter. Meteroids are smaller pieces of such debris. Comets are debris that contain both ice and rock.
PLANETS OUSTIDE OUR SOLAR SYSTEM
Astronomers have observed disks of gas and dust orbiting young stars.
At least 120 extrasolar planets have been discovered orbiting other stars.
Most of the extrasolar planets that have been discovered have masses around that of Jupiter.
Extrasolar planets are discovered indirectly.
There are 100,000,000,000 stars in our galaxy alone, called the Milky Way. And, there are at least 200 billion galaxies in the known universe that we are aware of!!! Astronomers have concluded that our universe is expanding, everything is moving away from us, meaning that at one time, everything was much closer together. This expansion... began about 13,700,000,000 years ago!
FORMATION OF OUR GALAXY:
1. GRAVITY BRINGS TOGETHER CLUMPS OF GAS AND DUST, THE SOLAR SYSTEM FORMED OUT OF LARGE SLOWLY ROTATING DISK.
2. THE CLOUDS STARTS TO COLLAPSE AND FLATTEN IN THE DIRECTION OF THE ROTATION. PROTOSTAR BEGINS TO FORM.
3. DKISK SPINS FASTER NOW, SUN/STAR BEGINS TO SHINE. GRAVITY MAKES IT SPIN FASTER.
4. THE HOT STAR/SUN BLOWS AWAY THE GAS AND ICE IN THE INNER SOLAR SYSTEM. IT LEAVES BEHIND ROCKS OF MANY SIZES, CALLED PLANETESIMALS.
5. MILLIONS OF PLANETESIMALS ORBIT THE SUN. A FEW PROTOPLANETS FORM FROM THE THEM. GRAVITY SLOWLY BRINGS THEM TOGETHER.
6. SOLAR SYSTEM AS WE KNOW IT TODAY, THE MOON AND A SMALL NUMBER OF PLANETS ORBIT THE SUN/STAR IN TEH SAME DIRECTION. OCASSIONALY THE PLANETS STILL GET HIT BY PLANETESIMALS.
Expanding universe
Astronomers thought our solar system was the centre of the universe until 1918, when American astronomer Harlow Shapley determined this was false by studying the distribution of star clusters. The existence of other galaxies was not proved until 1924, when American astronomer Edwin Powell Hubble identified the Andromeda galaxy, and others, with the aid of a powerful 100-inch telescope.
A star begins as a cloud of dust and gas, which condenses to form a single star, a two-star system also known as a binary star, or a star cluster.
The first telescope was built in the early 1600s, by Dutch lens-grinder Hans Lippershey.
A star’s colour depends on its temperature: blue stars have the highest temperatures, followed by yellow-white stars, and finally by red stars, which have the coolest temperatures.
If you have the opportunity to watch HUBBLE 3D please do, it will change the way to see the sky forever!
Hubble 3D at the iMax
THE NATURE OF LIGHT:
Photons, compact units of vibrating electric and magnetic fields, all carry energy through space at the same speed, "The speed of light".
Radio waves, infrared radiation, visible light, ultraviolet radiation, x rays, and gamma rays are the forms of electromagnetic radiation. They travel as photons, sometimes behaving as particles, sometimes as waves.
Visible light occupies only a small portion of the electromagnetic spectrum.
The wavelength of a visible light photon is associated with its colour. Wavelengths of visible light range from about 400 mn for violet to 700 nm for red light.
Infrared radiation and radio waves have wavelengths longer than those of visible light. Ultraviolet radiation, x rays, and gamma rays have wavelengths that are shorter.
The motion of an object toward or away from an observer causes the observer to see all the colours from the object to blueshift or redshift, respectively. This is generically called a Doppler Shift.
OPTICS AND TELESCOPES
A telescope's most important function is to gather as much light as possible. Its second function is to reveal the observed object in as much detail as possible. Often the least important function of a telescope is to magnify objets.
Reflecting telescopes, or refractors, produce images by bending light rays as they pass through glass lenses. Glass impurity, opacity to certain wavelengths, and structural difficulties make it inadvisable to build extremely large refractor. Reflector are not subject to many of the problems that limit the usefulness of refractors.
Charge coupled devices are used to record images.
Earth-based telescopes are being built with active and adaptive optics. These advanced technologies yield resolving power comparable to the Hubble Space Telescope.
NON OPTICAL ASTRONOMY
Radio telescopes have large reflecting antennas that are used to focus radio waves.
Very sharp radio images are produces with arrays of radio telescoped linked together in a technique called interferometry.
The Earth's atmosphere is fairly transparent to most visible light and radio waves, along with some infrared and ultraviolet radiation, arriving from space, but it absorbs much of the electromagnetic radiation at other wavelengths.
For observations at other wavelengths , astronomers mostly depend upon telescopes carried above the atmosphere by rockets. Satellite-based observatories are giving us a wealth of new information about the universe and permitting coordinated observation of the sky at all wavelengths.
LIGHT AND TELESCOPES
Since Newton, we have learned a lot about light. Newton discovered that white light sit he sum of the colours of the spectrum. White and black are not colours.
SPECTRUM:
Newton described light as particles made of different colours. Colour reflects only certain colour of light and absorbs all other colours. Purple= reflects purple light
red-long wave length
orange, yellow, green, blue, indigo, violet-short wave length
It is now known that light particles move as wavelengths.
Spectrum
By studying the wavelengths of electromagnetic radiation emitted and absorbed by an astronomical object, astronomers can learn about the object's temperature, chemical composition, companion objects, and movement through space.
BLACKBODY RADIATION:
A blackbody is a hypothetical object that perfectly absorbs electromagnetic radiation at all wavelengths. The radiation that it emits depends only on its temperature. Stars closely approximate black bodies.
Wien's law states that the dominant wavelength of radiation emitted by a blackbody is inversely proportional to its temperature. The intensities of radiation emitted at various wavelengths by a blackbody at a given temperature are shown as a blackbody curve.
The Stefan-Boltzmann law relates the temperature of a blackbody to the rate at which it radiates energy.
DISCOVERING SPECTRA
Spectroscopy- the study of electromagnetic spectra- provides important information about the chemical composition of remote astronomical objects.
Kirchhoff's three laws of spectral analysis describe the conditions under which absorption lines, emission lines, and a continuous spectrum can be observed. Spectral lines serve as distinctive "fingerprints" for the chemical elements and chemical compounds comprising a light source.
ATOMS AND SPECTRA:
An atom consists of of a small, dense nucleus (composed of protons and neutrons) surrounded by electrons. Different elements have different numbers of protons, different isotopes have different numbers of neutrons.
Quantum mechanics describes the behaviour of particles and shows that electrons can only be in certain allowed orbits around the nucleus.
The spectral lines of a particular element correspond to the various electron transition between allowed orbits of that element with different energy levels. When an electron shifts from one energy level to another, a photon of the appropriate energy (and hence a specific wavelength) is absorbed or emitted by the atom.
The spectrum of hydrogen at visible wavelengths consists of the Balmer series, which arises from electron transitions between the second energy level of the hydrogen atom and higher levels.
Every different element, isotope, and molecule has a different set of spectral lines.
When an atom loses or gains one or more electrons it is said to be charged. One way for it to lose an electron is for the electron to absorb an energetic photon and thereby fly free from its atom.
The equation describing the Doppler effect states that the size of a wavelength shift is proportional to the radial velocity between the light source and the observer.
VISIBLE LIGHT AND THE ELECTROMAGNETIC SPECTRUM
*ALL OBJECT SHINE BY THEIR OWN LIGHT...we can't usually see this, we can only see very hot object shining.
Wein's Law states that as the temperature of an object increases, the wavelength of light that is the maximum brightness of an object increases. This type of light, emitted by all objects, is called the black body radiation.
blackbody curve
ATOMS:
Have a dense central nucleus, almost all of the mass of the atom is in this nucleus. There are the positive protons, neutral neutrons, and orbiting this nucleus are the negatively charge electrons.
Atoms have very specific energy levels corresponding to the allowed orbits of electrons. Every type of element is different. Electrons can either be in their ground state, where they have not absorbed any energy, or when they absorb energy, they will be in their excited state, where they jump either one or several levels of orbit. They don't tend to hold onto the energy for too long though, and when they do let it go, they can either fall one level, or several, and even go back to their ground state. So we know that electrons can capture a proton, go up a level, and then randomly go back down. This shows that incoming light is absorbed if it is at the correct wavelength.
EARTH:
The Earth's atmosphere is about four-fifth's nitrogen and one-fifth oxygen. This abundance of oxygen is due to the biological processes of life-forms on the planet.
The Earth's atmosphere is divided into layers named the troposphere, stratosphere, mesosphere, and ionosphere. Ozone molecules in the stratosphere absorb ultraviolet light rays.
The outermost layer, or crust, of the Earth offers clues to the history of our planet.
The Earth's surface is divided into huge plates that move over the upper mantle. Movements of the plates, a process called plate tectonics, are caused by convection in the mantle, and upwelling of molten material along cracks in the ocean floor produces seafloor spreading. Plate tectonics is responsible for most of the major features of the Earth's surface, including mountain ranges, volcanoes, and the shapes of the continents and oceans.
Study of seismic waves (vibrations produced by earthquakes) shows that the Earth has small, solid, inner core surrounded by a liquid outer core. The outer core is surrounded by the dense mantle, which in turn is surrounded by the thin, low density crust. The Earth's inner and outer cores are composed primarily of iron with nome nickel mixed in it. The mantle is composed of iron-rich minerals.
The Earth's magnetic field produces a magnetosphere that surrounds the planet and blocks the solar wind.
Some charged particles from the solar winds are tapped in two huge, doughnut shaped rings called the Van Allen radiation belts. A deluge of particles from a coronal mass ejection by the Sun can initiate an auroral display.
IMPORTANT POINTS
- Orbit of the Earth around the Sun is not a circle, but an ellipse, something like an oval.
- The Sun is not in the centre of the ellipse, but off to the side.
- The reason that the Sun gets high in sky in Summer and low in the Winter is because the Earth is tilted in its orbit.
- The tilt of the Earth is 23 and 1/2 degrees
- One year for the Earth to orbit around the Sun
- Position of tilt stays in same direction in any position in orbit
- When it is Summer in the North Hemisphere , it is Winter in the South Hemisphere and vice versa.
IMPORTANT DATES
Spring Equinox, March 21 Sun highest in sky Light for exactly 12 hours
The actual hottest day is after June 21, because of the cumulative effect of lots of hot days, and the coldest day is after December 21, because of the cumulative effect of a lot of cold days.
Definitions:
STARS- shines by its own light
PLANETS- reflect light
MOONS- objects that orbit the planets
ASTEROIDS- smaller than planets, orbiting around the sun, mostly between Mars and Jupiter. Made of rock and iron.
KUIPER BELT OBJECTS- Small objects made of ice and rock, orbiting Sun beyond Neptune.
Seasons
* Tilt of Earth causes the Sun to be high in the sky during the Summer, or lower in the sky during the Winter.
THE MOON AND TIDES:
The Moon has light-coloured, heavily cratered highlands and dark coloured, smooth surfaced mare.
Many lunar rock samples are solidified lava formed largely of minerals also found in Earth rocks.
Anorthosite rock in the lunar highlands was formed between 4.0 billion and 4.3 billion years ago, whereas the mare basalts solidified between 3.1 and 3.8 million years ago. The Moon's surface has undergone very little geological change over the past 3 billion years.
Impact have been the only significant weathering agent on the Moon; the Moon's regolith was formed by meteoritic action. Lunar rocks brought back to Earth contain no water and are depleted of volatile elements.
Frozen water may have been discovered at the Moon's poles.
The collision-ejection theory of the Moon's origin, accepted by most astronomers, holds that that young Earth was struck by a huge asteroid, and debris from this collision coalesced to form the Moon.
The Moon was molten in its early stages, and the anorthosite crust solidified from low-density magma that floated to the lunar surface. The mare basins were created later by the impact of planetesimals and were then filled with lava from the lunar interior.
Gravitational and centrifugal interactions between the Earth and the Moon produce tides in the oceans of the Earth and set the Moon in synchronous rotation. The Moon is moving away from the Earth, and consequently, the Earth's rotation rate is decreasing.
On the picture below, imagine the Sun's light coming from the right.
http://shadowandsubstance.com/
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