Space and Astronomy
- The Universe is the sum total of all that exists in space and time.
- The study of the Universe is known as ‘ cosmology ’, which has its roots at the beginning of the 20th century with the introduction of Albert Einstein’s ” Theories of relativity “, which joined space and time into a single continuum.
What makes up the Universe
A galaxy is a huge aggregate of stars, gas and dust held together by gravitational attraction, usually in the form of a flattened disc, and generally with the matter being contained in spiral arms radiating away from the central nucleus of the disc.
The Milky Way is our own galaxy, one of 100 billion to a trillion known galaxies. Stars are globes of gas in which nuclear fusion reactions at the centre create vast quantities of energy which become radiated into space mainly in the form of light, heat and ultraviolet radiation. The Sun is the nearest star, the star at the centre of our solar system.
Planets are major – sized bodies directly orbiting a star. In the case of our own solar system there are eight planets. Now, Pluto is no longer considered to be a planet. Smaller bodies orbiting the Sun are given special names such as ‘ asteroids ’. A satellite is any body which orbits an object which is directly orbiting a star, i.e. a planet or smaller body.
The Big Bang Theory
The stars are moving and they are not fixed, as a result, it is known that the Universe is expanding. One consequence of this discovery was the realization that reversing time led to a contraction of the Universe to a point – like source or singularity. The origin of the Universe was therefore a cataclysmic event known popularly as the ‘ Big Bang ’. Since space and time also began at this point, there is no ‘ time ’ before the Big Bang. The original Big Bang theory, explains both the large – scale smoothness of the Universe and the small – scale non – uniformities ( that is, the clumping of matter into galaxies ).
This was done by suggesting that all parts of the Universe were in contact with each other during the critical period before 10 – 35 seconds, but that after this there was a 1050 expansion, possibly due to the separation of the strong force from the electro weak forces. Events in the Universe’s early history occurred very rapidly. All the light elements were initially formed within the first 15 minutes. Quarks, and leptons such as electrons and neutrinos, as well as an equal number of anti – particles, were formed after only 10-35 seconds but, by 10 – 32 seconds. After 100,000 years, when the temperature had fallen to 3700°C ( 6700°F ), ions and electrons joined together to form atoms of these light elements.
Proto – galaxies began to form when the temperature had reached 100°C ( 212°F ) and the formation of coherent galaxies is calculated to have begun one billion ( 109 ) years after the Big Bang. Proof of the Big Bang is considered to be the detection of the cosmic background radiation by Arno Penzias and Robert W. Wilson in 1965.
The Universe was filled with a ‘ sea ’ of cosmic radiation during its formation, and this has since cooled. The end of the Universe will be dire. Either it will expand for ever or reach an equilibrium size. In both cases all of the hydrogen will be used up and the Universe will die, or gravity will overcome the amount of mass in the Universe and it will collapse back to a point – like source.
Unit of Astronomy
Astronomical Unit ( AU ) : The mean distance of the Earth from the Sun as defined in 1938. The current value is 149,597,871 km.
Light Year ( ly ) : The distance travelled by light in vacuum in one tropical year of 365.24219878 mean solar days, that is 9,460,528,405,000 km.
Parsec ( pc ) : The distance at which an angle of one second of arc will represent the distance from the Earth to the Sun, that is 206,264.806 astronomical units or 3.2616 light years or 30,856,776,000,000 km.
The Solar System
- The solar system is located 26,100 light years from the centre of the Milky Way and was formed about 4540 million years ago from a globe of gas and dust.
- Most of the mass became concentrated in the central core to form the Sun, but part of the surrounding matter formed a flattened disc, which evolved into the eight planets ( now there are only 8 planets with Pluto being relegated to the status of Dwarf planet ) and other objects of the solar system.
The boundary between the inner and outer solar system is taken to be the orbit of Jupiter. The inner solar system consists of the four terrestrial planets, Mercury, Venus, Earth and Mars, as well as the asteroid belt.
The outer solar system comprises the four next planets – Jupiter, Saturn, Uranus and Neptune. These outer planets are all giant ‘ gas ’ planets; although they are all expected to have rock – iron cores, it is the composition and behaviour of the outer gas layers which gives each its unique characteristics.
Mercury’s surface is dominated by large basins representing different epochs in the formation of the crust. There are a large number of impact craters. The high density of the planet is due to its iron – rich core, which is 3600 km ( 2200 mi ) in diameter and accounts for 65 % of Mercury’s mass.
The atmospheric pressure is only one – trillionth ( 10 – 12 ) that of Earth and, without the protection of an atmosphere, there is a wide variation in surface temperature, from up to 420°C ( 790°F ) in the day down to – 180°C ( -290°F ) at night.
Although similar in size to Earth, Venus is an extremely hostile planet with an atmosphere rich in carbon dioxide. It has a surface pressure 94 times that of the Earth at an overall temperature of 464°C ( 867°F ).
A thick planet – wide cloud cover, 50 – 75 km above the surface, contains a high concentration of droplets of sulphuric acid, which may be due to emissions from active volcanoes. Although the surface cannot be seen from Earth, Venus is essentially flat ( with 80 % being within 1 km of the planet’s average radius ).
Venus does not have the same type of tectonic geological structure as the Earth, but appears to periodically undergo extensive resurfacing, so that the current surface is relatively young – only 500 million years old. Although the rotation period is longer than its year, a Venusian ‘ day ’ ( sunrise to sunrise ) is equivalent to 116 Earth days.
The Earth is the largest and densest of the inner planets, with an atmosphere consisting mainly of 78 % nitrogen and 21 % oxygen at an average temperature of 15°C ( 59°F ).
Two thirds of the surface is covered by oceans and the mean ( average ) sea level can be used as reference from which the maximum deviations are a depth of 11,022 m ( 36,160 ft ) for the Mariana Trench in the Pacific ocean and a maximum height of 8863 m ( 29,078 ft ) for Mount Everest in the Himalaya, a difference of 19.9 km – only 0.3% of the Earth’s radius.
With an equatorial diameter of 3476.3 km, a polar diameter of 3471.9 km and a mass of 7.348 x 1019 tonnes or 0.0123 Earth masses, the Moon is the fifth largest and fifth most massive satellite in our solar system.
Extensive space probe photography has now recorded the whole of the lunar surface showing the presence of craters, mountain ranges and broad plains of frozen lava known as ‘ seas ’ or ‘ maria ’. Because the Moon has no atmosphere, there is a wide variation in surface temperature, from 117°C ( 243°F ) at the Equator at mid – day to -163°C ( -261 °F ) after nightfall.
The current theory of the Moon’s formation is the ‘ giant impact theory ‘, suggesting that in the violent early history of the solar system, the newly formed Earth was struck by at least one and possibly several very large planetesimals.
Like Venus, the atmosphere of Mars is mainly carbon dioxide, but only at a surface pressure about 116th that of Earth at an average temperature of – 53°C ( -63°F ), which is 68°C ( 122°F ) lower than that of Earth.
The surface is highly complex, consisting of Flat Plains, Craters, Dormant Volcanoes and Pole Caps. There are also a number of large channels such as ‘ Valles Marineris ’, which is at least 4000 km long, up to 600 km wide and 7 km deep. It now appears that life on Mars could only have developed to a microbiological level.
Although there is evidence that many channels must have been fashioned by large quantities of water in the past, there is now no evidence of water in the outermost surface layers or in the atmosphere,although water ice is still present under the frozen carbon dioxide polar caps.
A model of Jupiter suggests that it may have a central rock iron core about 15,000 km in diameter, weigh about 15 Earth masses, and is surrounded by a shell of metallic hydrogen extending to a radius of 55,000km from its centre.
The ‘ Great Red Spot ’, which was first seen in 1664, is a long – lived swirling storm which rises up to 8 km above the surrounding cloud deck. The planet has a very strong magnetic field, about five to ten times stronger than that of the Earth. This results in the formation of extremely lethal radiation belts about 10,000 times more powerful than those of Earth.
The ring system on Jupiter was discovered in 1979 and has three components.
Saturn’s internal structure is generally considered to be similar to that of Jupiter, but with a much smaller metallic hydrogen layer extending to only 26,000 km from the centre of the planet. The true nature of Saturn’s rings, initially vaguely observed by Galileo in 1610, was deduced by Christian Huygens ( Netherlands ) in 1659. Composed mainly of water ice, the main ring system is 273,550 km in diameter, but only about 10 m ( 33 ft ) thick.
Although officially Saturn has eighteen satellites, many more candidates have been observed from re – examination of photographs from the Voyager 2 encounter and from Hubble Space Telescope observations. The largest of the moons, Titan, is the only satellite in the solar system with an extensive atmosphere.
Uranus can just be seen with the naked eye, this much smaller gas planet is believed to have a rock-iron core surrounded by a ‘ sea ’ of water, methane and ammonia. The outer atmosphere is composed mainly of hydrogen, but with about 26 % of helium and a small amount of methane, which is responsible for the greenish colour of the atmosphere.
The large tilt of Uranus’s axis ( 98° ) means that day and night on some parts of the planet may last up to 21 years, but the sunlit ‘ south ’ pole and dark ‘ north ’ pole differ very little in temperature.
The planet Neptune is invisible to the naked eye. Neptune is an extremely dynamic world with many discernible cloud
features and extremely high wind speeds. The planet radiates 161 % more heat back into space than it receives from the Sun. The bluish colour of the planet is due to the presence of methane in the atmosphere.
The Voyager 2 encounter proved that there were three distinct rings and a diffuse ring of material between 38,000 to 59,000 km from Neptune’s centre.
In 1989, the Voyager imaging team discovered six new satellites in addition to the two already known. The largest of the satellites, Triton, has a large orbital inclination ( 157° ) and a retrograde orbit ( opposite to the direction of Neptune’s rotation ).
At the centre of the solar system is the Sun, a mass composed of 73 % hydrogen, 25 % helium and 2 % other elements.
The internal structure of the Sun consists of a helium – rich core, in which hydrogen undergoes fusion to helium. The atmosphere of the Sun consists of a ‘ chromosphere ’, which extends to about 10,000 km above the photosphere.
It has a sufficiently high temperature. The chromosphere only becomes visible during total eclipses, when the photosphere is blocked out. The outer atmosphere or ‘ corona ’ is an extremely thin gas at a high temperature which appears as a white halo.
It allows the continuous dispersal into space of the Sun’s matter in the form of a plasma of charged particles. This ‘ solar wind ’ permeates the whole of the solar system. Solar flares are huge jets of gas flung many thousands of kms from the chromosphere.
Inner Solar System
The Solar System has been broken down into two major parts by astronomers :
The inner Solar System and the outer Solar System. The four terrestrial planets and all material inside of the main asteroid belt comprise the inner Solar System. This article will concentrate on the three terrestrial planets other than our own : Mercury, Jupiter, and Mars.
Mercury is the least explored terrestrial or ” rocky “ planet in our solar system. Previously NASA’s only encounters with the innermost planet were the three flybys performed in 1974 and 1975 by the Mariner 10 mission that mapped 45 percent of the planet’s surface. In January 2008, the ” MESSENGER ” spacecraft flew by Mercury for its first of three fly – bys. As it begins to reveal the planet’s composition and history, it will in turn, help scientists understand more about our home planet and its place in the inner solar system.
Earth’s Moon has a special place among the objects of the solar system, as it is the only body other than Earth where humans have journeyed to and where humans will return relatively soon. NASA is sending robotic missions to the moon to prepare for mans’ prolonged habitation on the lunar surface which ultimately will help man reach for Mars and attain the goals set forth in the Vision for Space Exploration ( VSE ). Studying the Moon and its history provides insight on the formation history of the Earth – Moon system and events that shaped the inner solar system.
Mars is a highly attractive object of study :
Not only does it provide an excellent laboratory for studying planetary evolution in the context of the Earth and Venus, but it is the most compelling target in the solar system to search for life’s existence beyond Earth. Additionally, Mars is an eventual goal of the Vision for Space Exploration’s human spaceflight program. Finally, Mars is relatively easily accessed with launch opportunities occurring approximately every 2 years. For these reasons, the Mars Exploration Program is a fully integrated program, designed to maximize the scientific return, technology infusion, and public engagement of the robotic exploration of the Red Planet. Each strategic mission of the program has both technological and scientific linkages to previous missions and orbiters, and landers support each other’s operations.
Venus has often been described as Earth’s sister planet since the two are very similar in size and bulk composition, although they evolved to very different ends. Venus is not currently targeted by any NASA missions although future mission concepts include the Venus In Situ Explorer ( VISE ) and Venus Mobile Explorer ( VME ) that would investigate the surface of Venus and help understand the climate change processes that led to the extreme conditions of Venus today. A Venus Surface Sample Return ( VSSR ) mission is also being considered. These missions remain long – range goals for Venus exploration.
Outer Solar System
Planetary Science missions to the outer planets help reveal secrets about the solar system by observing those outer distant worlds up close. Jupiter’s moon Europa and Saturn’s moon Enceladus are now thought to hide liquid water beneath their frozen surfaces and are high priority targets for NASA. Unlocking their secrets and those of the outer planets will help scientists understand more about planet Earth and the formation and evolution of the solar system.
Jupiter has more mass than all other planets in the solar system combined. It helps protect Earth by steering comets either towards the sun or ejecting them to the outer reaches of the solar system or beyond. Jupiter has dozens of moons orbiting it, one of which, Europa, is thought to have a sub – surface liquid salt water ocean. It therefore may possibly harbor life as heat and water, the two ingredients required for life on Earth as we know it, are seemingly present below the moon’s surface.
Saturn, is the sixth from the sun. Another Jovian planet, Saturn is also primarily condensed gas, with a minute rocky core. The contraction of the planet caused the enormous pressure of Saturn’s atmosphere causes so much heat, that it radiates as much into space as it receives from the sun. Saturn is perhaps best known for its rings, which are known by their letter designation, indicating when they were discovered. From the planet outward, they are D, C, B, A, F, G, and E rings, which are comprised of hundreds of thousands of ringlets.
Neptune poses a number of important questions regarding how giant planets form and what truncates the formation of multiple giant planets in a planetary system. Residing on the edge of our planetary system, Neptune may hold, deep in its interior, chemical clues concerning the nature of the rocky and icy debris that formed the giant planets. A comprehensive study of Neptune, and its moon Triton, is considered a priority for the third decade by the Solar System Exploration road map team.
Uranus – Over the 2006 – 2016 time frame, there are no strategic missions planned to Uranus and only one spacecraft, the extremely productive Voyager II, has ever visited the distant planet. Ultimately, deep – entry probes into Uranus will be necessary in order to understand its composition and compare it to that of the other ” water giant “, Neptune.
Stars are accretions of gas that radiate energy through nuclear fusion reactions. Stars form from the gravitational contraction of a cloud of gas and dust with a central core forming rapidly and the remainder of the surrounding cloud falling onto the core to form the star.
The gravitational collapse continues until the core is both hot and dense enough to initiate the nuclear fusion of hydrogen to helium. The vast amount of energy produced counteracts the gravitational collapse and the star achieves a state of equilibrium which can last up to 10,000 million years in the case of a star the size of the Sun, but only about one million years for a very massive star. Eventually a critical amount of hydrogen will have been used up, nuclear fusion will cease, and the core will again start to contract.
This releases gravitational energy, resulting in fusion reactions in the hydrogen envelope which surrounds the core. This ‘ shell ’ swells up and, because of the reduced temperature, glows red rather than white and the star becomes a ‘ red giant ’.
For stars about the size of our Sun, core collapse continues until the electron fields surrounding the nuclei of the atom become compressed and the core density reaches about 100,000 times the density of the Earth. Such a core may then be the size of the Earth, but a mass equal to that of the Sun.
For stars in excess of 50 solar masses, the core collapse is so extreme that the whole mass may collapse into a single point. The intense concentration of mass causes a distortion of local space – time to such an extent that even radiation (i.e. light) cannot escape from the ‘ sphere of influence ’, which theoretically extends to a radius of 29.5 km for a ten solar mass core, and would therefore appear as a ‘ black hole ’ with a diameter of 59 km.
- Galaxies result from the accumulation of gas on to the proto – galaxies, which were formed by density fluctuations and gravity instabilities in the expanding primordial fireball.
- The proto – galaxies appear to have formed on the ‘ surfaces ’ of ‘ bubbles ’, each about 100 million light years in diameter, and in the process the centres of the bubbles became virtually devoid of matter.
There are estimated to be between 100 billion and a trillion ( 1011 to 1012 ) galaxies, each containing about 100 billion stars, so the number of stars is between 1022 and 1023.
Hubble classified galaxies into three types :
Elliptical, Spiral and Irregular. Lenticular ( lensshaped ) galaxies are intermediate between the elliptical and spiral galaxies.
The centres of regular – shaped galaxies are believed to contain massive black holes with masses millions to billions times that of the Sun.
Space environment is a branch of astronautics, aerospace engineering and space physics that seeks to understand and address conditions existing in space that affect the operation of spacecraft. A related subject, space weather, deals with dynamic processes in the solar – terrestrial system that can give rise to effects on spacecraft, but that can also affect the atmosphere, ionosphere and geomagnetic field, giving rise to several other kinds of effects on human technologies.
Effects on spacecraft can arise from radiation, space debris and meteoroid impact, upper atmospheric drag and spacecraft electrostatic charging.
Overview on Space Environment
The Space Environments and Technology Archive System ( SETAS ) has been established to preserve and provide easy access to the diverse collection of space environments and technology ( SET ) resources. The resources are organized according to technical disciplines and data sources.
The technical disciplines are meant to encompass the varied aspects of the space environment and their effects. These include ionizing radiation, meteoroids and debris, neutral external contamination, plasmas and fields, thermal and solar, electromagnetic effects, materials and processes, and systems.
Space Environment Impacts on Systems
The origin of space environmental impacts on radar, communications and space systems lies primarily with the sun. The sun is continuously emitting electromagnetic energy and electrically charged particles. Superimposed on these emissions are enhancements in the electromagnetic radiation ( particularly at X – ray, Extreme Ultra Violet ( EUV ) and Radio wavelengths ) and in the energetic charged particle streams emitted by the sun. These solar radiation enhancements have a significant potential to influence DOD operations.
The Milky Way Galaxy
Our galaxy is considered to be a typical spiral galaxy about 75,000 light years in diameter. It is a member of the so – called ‘ Local Group ‘ of about 20 galaxies, which is about 6 million light years in extent and which is dominated at one end by our own galaxy and at the other by the much larger Andromeda galaxy.
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