Guide to Space Archives

November 5, 2010July 21, 2020 by Matt Williams

What is the Multiverse Theory?

*Could our Universe be part of a wider Multiverse? And could these other Universes support life? Credit: Jaime Salcido/EAGLE Collaboration*

If you’re a fan of science fiction or fantasy then chances are, at some point, you’ve read a book, seen a movie, or watched a series that explored the concept of multiple universes. The idea being that within this thing we call time and space, there are other dimensions where reality differs from our own, sometimes slightly, sometimes radically. Interestingly enough, this idea is not restricted to fiction and fantasy.

In science, this is known as the Multiverse Theory, which states that there may be multiple or even an infinite number of universes (including the universe we consistently experience) that together comprise everything that exists: the entirety of space, time, matter, and energy as well as the physical laws and constants that describe them. In this context, multiple universes are often referred to as parallel universes because they exist alongside our own.

The term was coined in 1895 by the American philosopher and psychologist William James. However, the scientific basis of it arose from the study of cosmological forces like black holes and problems arising out of the Big Bang theory. For example, within black holes it is believed that a singularity exists – a point at which all physical laws cease – and where it becomes impossible to predict physical behavior.

Beyond this point, it is possible that there may be an entirely new set of physical laws, or just slightly different versions of the ones that we know, and that a different universe might exist. Theories like cosmic inflation support this idea, stating that countless universes emerged from the same primordial vacuum after the Big Bang, and that the universe as we know it is just what is observable to us.

Max Tegmark’s taxonomy of universes sums up the different theories on multiple universes. IN this model, there are four levels that classify all major schools on thought on the subject.

In Level One, different universes are arranged one on top of the other in what is called Hubble Volumes, all having the same physical laws and constants. Though each will likely differ from our own in terms of distribution of matter, there will eventually be Hubble volumes with similar, and even identical, configurations to our own.

In Level Two, universes with different physical constants exist and the multiverse as a whole is stretching and will continue to do so forever, but some regions of space stop stretching and form distinct bubbles, like gas pockets in a loaf of rising bread.

In Level Three, known as the Many Worlds Interpretation of Quantum Mechanics, observations cannot be predicted absolutely but a range of possible observations exist, each one corresponding to a different universe. Level Four, aka.the Ultimate Ensemble devised by Tegmark himself, considers as equally real all universes that can be defined by mathematical structures. In other words, universes with the same or different constants may exist.

We have written many articles about multiverse for Universe Today. Here’s an article about searching life in the multiverse, and here’s an article about parallel universe.

If you’d like more info on the Multiverse, check out some Recent Innovations about the Concept of Universe, and here’s a link to an article about the Size of the Universe.

We’ve also recorded an entire episode of Astronomy Cast all about Multiverses. Listen here, Episode 166: Multiverses.

Sources:
http://en.wikipedia.org/wiki/Multiverse
http://www.sciencedaily.com/releases/2010/01/100112165249.htm
http://www.astronomy.pomona.edu/Projects/moderncosmo/Sean%27s%20mutliverse.html
http://en.wikipedia.org/wiki/William_James
http://en.wikipedia.org/wiki/Big_Bang
http://en.wikipedia.org/wiki/Inflation_%28cosmology%29

November 5, 2010December 24, 2015 by Matt Williams

Morning Star

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If you look to the morning sky – to the east that is, as the sun’s rising – you will notice a bright star in the firmament, one that should not be there. Theoretically, stars only come out at night and should be well on their way to bed by the time the sun rises, correct? Well, that’s because the Morning Star, as it’s known, isn’t a star at all, but the planet Venus. It is both the morning and evening star, the former when it appears in the east during sunrise and the latter when it appears in the west during sunset. Because of its unique nature and appearance in the sky, this “star” has figured prominently in the mythologies of many cultures.

In ancient Sumerian mythology, it was named Inanna (Babylonian Ishtar), the name given to the goddess of love and personification of womanhood. The Ancient Egyptians believed Venus to be two separate bodies and knew the morning star as Tioumoutiri and the evening star as Ouaiti. Likewise, believing Venus to be two bodies, the Ancient Greeks called the morning star Phosphoros (or Eosphoros) the “Bringer of Light” (or “Bringer of Dawn”) and the evening star they called Hesperos (“star of the evening”). By Hellenistic times, they had realized the two were the same planet, which they named after their goddess of love, Aphrodite. The Phoenicians, never ones to be left out where astronomy and mythology were concerned, named it Astarte, after their own goddess of fertility. In Iranian mythology, especially in Persian mythology, the planet usually corresponds to the goddess Anahita, and sometimes AredviSura, the goddesses of fertility and rivers respectively. Mirroring the ancient Greeks, they initially believed the planet to be two separate objects, but soon realized they were one.

The Romans, who derived much of their religious pantheon from the Greek tradition and near Eastern tradition, maintained this trend by naming the planet Venus after their goddess of love. Later, the name Lucifer, the “bringer of light”, would emerge as a Latinized form of Phosphoros (from which we also get the words phosphorus and phosphorescence). This would prove influential to Christians during the Middle Ages who used it to identify the devil. Medieval Christians thusly came to identify the Morningstar with evil, being somewhat more concerned with sin and vice than fertility and love! However, the identification of the Morningstar as a symbol of fertility and womanhood remains entrenched, best demonstrated by the fact that the astronomical symbol for Venus happens to be the same as the one used in biology for the female sex: a circle with a small cross beneath.

The Morningstar also figures prominently in the mythology of countless other cultures, including the Mayans, Aborigines, and Maasai people of Kenya. To all of these cultures, the Morningstar still serves as an important spiritual, agricultural and astrological role. To the Chinese, Japanese, Koreans and Vietnamese, she is known literally as the “metal star”, based on the Five Elements.

We have written many articles about the Morning Star for Universe Today. Here’s an article about how to find Venus in the sky, and here’s an article about the brightest planet.

If you’d like more information on the Morning Star, check out Hubblesite’s News Releases about Venus, and here’s a link to NASA’s Solar System Exploration Guide on Venus.

We’ve also recorded an entire episode of Astronomy Cast all about Venus. Listen here, Episode 50: Venus.

Sources:
http://en.wikipedia.org/wiki/Morning_Star
http://en.wikipedia.org/wiki/Lucifer
http://en.wikipedia.org/wiki/Eosphorus
http://en.wikipedia.org/wiki/Venus
http://en.wikipedia.org/wiki/Isis
http://en.wikipedia.org/wiki/Evening_star

November 4, 2010February 6, 2017 by Matt Williams

What is Plutonium?

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The name itself conjures up imagines of mini nukes and sophisticated space-age gadgets doesn’t it? Well for some people it does. For others, Plutonium (Pu, atomic number of 94 on the periodic table of elements) spawns images of nuclear reactors, atomic energy and nuclear waste. All of these are true to an extent, but the reality behind this radioactive element is understandably more complex. For starters, plutonium is a silvery white actinide metal that is radioactive, and hence quite dangerous when exposed to living tissue. It is one of the key ingredients in the making of atomic weapons, but is also produced in nuclear reactors as a result of slow fission. There are also several isotopes of the element, but for our purposes, the most important is Plutonium-239, a fissile isotope that is used for both nuclear power and weapons and has a half-life of 24,100 years.

Plutonium-238 was first discovered as an element on Dec.14th1940, and then chemically identified on February 23rd 1941through the deuteron bombardment of Uranium in a cyclotron by Glenn T. Seaborg and his team of scientists, working out of the University of California in Berkley. The team submitted a paper publishing their findings; however, this paper was retracted when it became clear that Plutonium-239 was a fissile material that could be useful in the construction of an atomic weapon. At this time, the US was deep into the development of an atomic bomb (aka. the Manhattan Project) because it was believed that Germany was doing the same. For this reason, publication of Seaborg’s work was delayed until 1946, a year after the Second World War ended and security surrounding atomic research was no longer a concern. Seaborg decided to name the element after Pluto because of the recent discovery of element 93, Neptunium, and felt that element 94 should accordingly be named after the next planet in the Solar System.

Towards the end of WWII, two nuclear reactors were created which would produce the plutonium used in the construction of “Trinity”, “Fat Man” and other atomic weapons. These were the X-10 Graphite Reactor facility in Oak Ridge (which later became the Oak Ridge National Laboratory) and the Hanford B reactor (built in 1943 and 45 respectively). Large stockpiles were subsequently built up by the US and USSR during the Cold War, and have since become the focus of nuclear proliferation treaty concerns. Today, it is estimated that several tonnes of plutonium isotopes exist in our biosphere, the result of atomic testing during the 1950’s and 60’s.

We have written many articles about Plutonium for Universe Today. Here’s an article about Plutonium shortage in NASA, and here’s an article about Plutonium – 238.

If you’d like more info on Plutonium, check out Wikipedia – Plutonium, and here’s a link to World Nuclear page about Plutonium.

We’ve also recorded an entire episode of Astronomy Cast all about Nuclear Forces. Listen here, Episode 105: The Strong and Weak Nuclear Forces.

Sources:
http://en.wikipedia.org/wiki/Plutonium
http://www.world-nuclear.org/info/inf15.html
http://periodic.lanl.gov/elements/94.html
http://en.wikipedia.org/wiki/Nuclear_proliferation
http://en.wikipedia.org/wiki/Actinide
http://en.wikipedia.org/wiki/Cyclotron

November 4, 2010February 6, 2017 by Matt Williams

What is a Plutoid?

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Pluto, we hardly knew ya! Don’t worry, she’s not going anywhere. However, this once happy planet will no longer be listed amongst the “planets” in our solar system. According to International Astronomical Union (IAU), which began meeting in August of 2006, the term Plutoid now applies to Pluto, as well as any other small stellar body that exist beyond the range of Neptune. Arriving at this working definition in 2008, two years after first meeting, the IAU defines the term Plutoids thusly: “Plutoids are celestial bodies in orbit around the Sun at a semimajor axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit.”

The reason the IAU began meeting in the first place was to iron out some ambiguities that exist in the terminology of astronomy. For example, thought some might find it shocking, astronomers had never actually come up with a definition of “planet”. Originally, a planet meant a “wandering star” – ie. a star that appeared to move from constellation to constellation. This was the definition used by ancient astronomers, and it applied to the sun and moon as well. However, Copernicus’s heliocentric model changed all that; now it was clear that the Earth was a planet itself and moved around the Sun with the rest of them. In addition, more and planets were being discovered beyond Jupiter, such as Uranus and Neptune, and then between Jupiter and Mars. This included Ceres, Pallas, Vesta, and Juno, but astronomers soon realized that these bodies were far too small to fit with the rest of the planets.

Then came Pluto’s discovery. At the time, scientists thought it to be several times larger than it actually was; accordingly they placed it on the list of planets. Eventually, its true size was realized and other bodies similar to Pluto in size and composition were found far beyond Neptune, in what is known as the Kuiper Belt. Pluto was to these stellar objects what Ceres was to large objects in the asteroid belt – that is to say, comparable in size. Astronomers proposed several names for these objects, but matters did not come to a head until Eris was discovered. This dwarf planet was actually larger than Pluto, 2500 km in diameter, making it twenty-seven percent larger than Pluto.

In the end, the IAU could only resolve this matter by removing Pluto from the list of planets and devising a new category for dwarf planets that could no longer be considered true planets. Plutoid was the result, and now applies to the trans-Neptunian objects of Pluto, Haumea, Makemake, and Eris.

We have written many articles about Plutoid for Universe Today. Here are some facts about Pluto, and here’s an article about why Pluto is no longer a planet.

If you’d like more info on Pluto, check out Hubblesite’s News Releases about Pluto, and here’s a link to NASA’s Solar System Exploration Guide to Pluto.

We’ve also recorded an episode of Astronomy Cast dedicated to Pluto. Listen here, Episode 64: Pluto and the Icy Outer Solar System.

Sources:
http://en.wikipedia.org/wiki/Plutoid
http://astroprofspage.com/archives/1685
http://www.sciencedaily.com/releases/2008/06/080611094136.htm
http://en.wikipedia.org/wiki/Eris_%28dwarf_planet%29

October 31, 2010December 24, 2015 by Jerry Coffey

Why Is The Sunset Red?

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Why is the sunset red? Awesome question. The most basic answer is that light is refracted by particles in the atmosphere and the red end of the spectrum is what is visible. To better understand that you have to have a basic understanding of how light behaves in the air, the atmosphere’s composition, the color of light, wavelengths, and Rayleigh scattering and here is all of the information that you need to understand those things.

The Earth’s atmosphere is one of the main factors in determining what color a sunset is. The atmosphere is made up mostly of gases with a few other molecules thrown in. Since it completely surrounds the Earth it affects what you see in every direction. The most common gasses in our atmosphere are nitrogen(78%) and oxygen(21%). The remaining single percent is made up of trace gasses, like argon, and water vapor and many small solid particles, like dust, soot and ashes, pollen, and salt from the oceans. There may be more water in the air after a rainstorm, or near the ocean. Volcanoes can put large amounts of dust particles high into the atmosphere. Pollution can add different gases or dust and soot.

Next, you have to look at light waves and the color of light. Light is an energy that travels in waves. Light is a wave of vibrating electric and magnetic fields and is a part of the electromagnetic spectrum. Electromagnetic waves travel through space at the speed of light(299,792 km/sec). The energy of the radiation depends on its wavelength and frequency. A wavelength is the distance between the tops of the waves. The frequency is the number of waves that pass by each second. The longer the wavelength of the light, the lower the frequency, and the less energy it contains. Visible light is the part of the electromagnetic spectrum that our eyes can see. Light from a light bulb or the Sun may look white, but it is actually a combination of many colors. Light can be split into its different colors with a prism. A rainbow is a natural prism effect. The colors of the spectrum blend into one another. The colors have different wavelengths, frequencies, and energies. Violet has the shortest wavelength meaning that it has the highest frequency and energy. Red has the longest wavelength and lowest frequency and energy.

In order to put it all together, we have to look at the action of light in the air of our planet. Light moves in a straight line until it is interfered with(gas molecule, dust, or anything else). What happens to that light depends on the wavelength of the light and size of the particle. Dust particles and water droplets are much larger than the wavelength of visible light, so it bounces off in different directions. The reflected light appears white because it still contains all of the same colors, but gas molecules are smaller than the wavelength of visible light. When light bumps into them it acts differently. After light hits a gas molecule some of it may get absorbed. Later, the molecule radiates the light in a different direction. The color that is radiated is the same color that was absorbed. The different colors of light are affected differently. All of the colors can be absorbed, but the higher frequencies (blues) are absorbed more often than the lower frequencies (reds). This process is called Rayleigh scattering.

Long story short,, the answer to ‘why is the sunset red?’ is: At sunset, light must travel farther through the atmosphere before it gets to you, so more of it is reflected and scattered and the sun appears dimmer. The color of the sun itself appears to change, first to orange and then to red because even more of the short wavelength blues and greens are now scattered and only the longer wavelengths(reds, oranges) are left to be seen.

We have written many articles about the sunset for Universe Today. Here’s an article about sunrise and sunset, and here are some sunset pictures.

If you’d like more info on the Sun, check out NASA’s Solar System Exploration Guide on the Sun, and here’s a link to the SOHO mission homepage, which has the latest images from the Sun.

We’ve also recorded an episode of Astronomy Cast all about the Sun. Listen here, Episode 30: The Sun, Spots and All.

Reference:
NASA Space Place

October 31, 2010December 24, 2015 by Tega Jessa

How Hot is Lava

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We all know that the lava is molten rock that is spewed from a volcano. However how hot is lava? The temperature of lava can range anywhere from 700° C to 1200° C. Lava is not really lava until it meets the earth’s crust before that it is known as magma. Magma is the ocean of molten rock that lies beneath the earth’s crust. When it escapes through cracks the earth’s crust it creates volcanoes. The magma that comes out of volcanoes is what we call lava. Lava can be as much 100,000 times as viscous as water.

The different types of lava vary depending on composition and temperature. The three main types of lava are felsic, intermediate, and mafic. There are two types of felsic lava. They are rhyolite and dacite. These types of lava are composed of aluminum, silica, potassium, sodium, calcium, and liquid quartz and feldspar. Felsic lava normally erupts between 650° C to 750° C.

Intermediate lava is the next type of lava. Intermediate lava is also known as andesitic lava. Andesitic lava has lower levels of aluminium and silica. However this kind of lava is richer in magnesium and iron than felsic lava. This kind of lava occurs on steep composite volcanoes like those found in the Andes mountain range. Since andesitic lava has a lower level of aluminum and silica in its composition it is normally hotter with a range of 750-950° C.

The last type of lava is mafic lava or basaltic lava. This is one of the hottest types of lava coming out at temperatures exceed 950 degrees Celsius. This type of lava is rich in iron bearing minerals. This is what accounts for as high temperature. There are also the kinds of mafic lava that are even a hotter than normal basaltic lava. One type is all ultra-mafic lava.

Lava temperature tells us a lot about the different types of lava. Each brings important minerals and nutrients to the surface. So getting a better understanding of lava flows gives a better of the Earth’s composition and how certain minerals came to the surface of the Earth’s crust.

We have written many articles about lava for Universe Today. Here’s an article about the types of lava, and here’s an article about the viscosity of lava.

If you’d like more info on lava and volcanoes, take a look at the USGS’ Volcanoes Hazard Program, and here’s a link to Volcano World from Oregon State University.

We’ve also recorded an episode of Astronomy Cast all about volcanoes. Listen here, Episode 141: Volcanoes, Hot and Cold.

References:
NASA Earth Observatory
USGS

October 31, 2010December 24, 2015 by Tega Jessa

How Fast Does Light Travel

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One of the most interesting constants and challenges in physics is the speed of light. The speed of light has a lot of important implications for physics from General Relativity to the search for a unified theory. Physicists and aeronautics engineers designing future space craft see it as the last great barrier to practical interstellar travel. So how fast does light travel?

We know that light has a finite speed and it travels at the speed of 300,000 kilometers per second. This a great distance to travel. On earth this speed is almost instantaneous. However we now know that its limits can be determined on the larger scale of space. For example it takes about 8.3 minutes for light from the Sun to reach the Earth. To reach the nearest star to the Solar System it takes about 3 to 4 years. This limitation of light is what we call the light speed barrier.

In the early days of science the argument of whether the speed of light was instantaneous or not was a major source of debate. As early as the Greeks, there were proponents that argued for both a finite and infinite speed for light. There were also writings during the 11th century by Arab philosophers that proposed that the speed of light depended on the medium it traveled through. It would not be until the 20th century that physicists such as Planck and Einstein would discover the actual speed of light and light’s properties.

As mentioned earlier the speed of light does change. It is actually only 300,000 km in a vacuum. The speed varies slightly in air and other mediums depending on transparency and refractive quality. The speed of light however tends to still be considerably faster than that of others waves such as sound waves. It was also discovered that the speed of light applies to all forms of electromagnetic radiation not just visible light. Physicists are also proposing that the speed of light also applies to gravity waves.

Understanding of the speed of light has led to some interesting theories in physics. Many of them can be found in Einstein’s theories of General Relativity and Special relativity. First off, only massless particles such as photons can naturally reach the speed of light otherwise it would take essentially infinite energy to reach this speed. However objects with mass can theoretically achieve a significant percentage of light speed. It is also proposed that even if light speed could be reach it would produce certain side effects. One is time dilation where while traveling at light speed a Rip Van Winkle effect occurs where years would pass by for observers while a person traveling at light speed would only experience moments of time in the same perceived period. It has also been theorized exceed light speed would lead to time travel.

We have written many articles about light for Universe Today. Here’s an article about gravity moving at the speed of light, and here’s an article about galaxies moving faster than the speed of light.

If you’d like more info on the speed of light, check out The Speed of Light According to Einstein, and here’s a link to The Speed of Light on a Rocket by NASA.

We’ve also recorded a Question Show about the Speed of Light. Check it out!

Sources:
Wikipedia: Speed of Light
Wikipedia: Time Travel
Newton Ask a Scientist!
University of Illinois

October 31, 2010December 24, 2015 by Tega Jessa

How Does a Compass Work

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Compasses are some of the oldest navigational tools in history. Since Mankind started to understand more about Navigation they have been crucial to major feats of navigation such as the first transoceanic voyages and the circumnavigation of the globe. None of this would be possible without the aid of the compass in performing navigation calculations over long distances. Early explorers had to use local landmarks and the stars to navigate. This made it very difficult to travel to far or unknown destinations. Compasses were one of the key breakthroughs that made such voyages a reality. So how does a compass work?

A compass works by detecting the Earth’s natural magnetic fields. The Earth has an iron core that is part liquid and part solid crystal due to gravitational pressure. It is believed that movement in the liquid outer core is what produces the Earth’s magnetic field. Like all magnetic fields the Earth’s magnetic field has two main poles, a north and south pole. These magnetic poles are slightly off from the Earth’s axis rotation which is used as the basis of the geographic poles, but they are close enough that the general directions with adjustments for the polar difference, called a declination, can be used for navigation.

Essentially a compass is a light weight magnet, generally a magnetized needle, on a free rotating pivot. This allows the needle to better react to nearby magnetic fields. Since opposites attract the southern pole of the needle is attracted to the Earth’s natural magnetic north pole. This is how navigators are able to discern north. The Earliest compasses were water compasses invented by the Chinese during the Song dynasty. These were a magnetized piece of metal floating in a bowl of water. The water provides the first frictionless pivot needed for making a working compass.

The compass later came into common use in the west during the 14th century AD. This led to what is now known as the Age of Exploration where major European powers started further exploration of the World including North and South America. While the compass was just one of the devices that brought about this golden age of exploration it played an important part in bring it to pass. Even now modern navigation to some point still relies on compasses and the more accurate maps they helped to develop.

We have written many articles about the compass for Universe Today. Here’s an article about the inventions of Galileo, and here’s an article about bar magnets.

If you’d like info on Earth’s magnetic field, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about Magnetism. Listen here, Episode 42: Magnetism Everywhere.

Sources:
USGS
How Stuff Works

October 24, 2010December 24, 2015 by Matt Williams

Last Day of Summer

Winter Solstice — Earth as viewed from the cabin of the Apollo 11 spacecraft. Credit: NASA

Summertime is a joyous time for so many reasons. There’s the sense of vacation, that feeling of freedom we remember so fondly from our childhoods. There’s the warmth weather, the sunshine, the early mornings and cool, late evenings. Seriously, there’s nothing wrong with summer, except the unfortunate fact that sooner or later, it has to end.

But when exactly is the very last day of summer? Well, it differs from place to place, depending on your location, whether you are north or south of the equator and by how much. But in the Northern Hemisphere, the change in seasons occurred on September 22nd for the year of 2010. In the Southern Hemisphere, it took place on February 28th.

In order to understand why this date was pegged as the end of the season, we need to understand exactly how the season itself is measured. These have to do with the equinoxes and solstices, seasonal markers that occur twice a year respectively. From an astronomical point of view, the equinoxes and solstices are in the middle of the respective seasons, but a variable seasonal lag means that the meteorological start of the season, which is based on average temperature patterns, occurs several weeks later than the start of the astronomical season.

According to meteorologists, summer extends for the whole months of June, July and August in the northern hemisphere and the whole months of December, January and February in the southern hemisphere. Interestingly enough, in this hemisphere, the end of the summer season is also dependent on whether or not it is a leap year (during leap years, an extra day is added).

In North America, summer is often fixed as the period from the summer solstice (June 20 or 21, depending on the year) to the fall equinox (September 22 or 23, again depending on the year). Therefore, Sept. 22 was the last day of summer and the beginning of the 2010 autumnal equinox, which officially began at 11:09 p.m. EST., the full moon having peaked the following morning at 5:17 a.m. EST which marked it as the first day of fall in the Northern Hemisphere.

The moon closest to the September equinox is considered the “Harvest Moon.” Its name stems from when farmers would rely on the light to work in the fields as the days grew shorter. For the first time since 1991, the full moon fell on the equinox, creating a “Super Harvest Moon.” In the Southern Hemisphere, the last day of summer was February 28th since 2010 was not a leap year.

We have written many articles about Summer for Universe Today. Here’s an article about the summer solstice, and here’s an article about the Earth seasons.

If you’d like more info on Earth, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:
http://en.wikipedia.org/wiki/Summer
http://www.tonic.com/article/last-day-of-summer-first-night-of-fall-super-harvest-moon/
http://en.wikipedia.org/wiki/Equinox
http://en.wikipedia.org/wiki/Solstice
http://wiki.answers.com/Q/What_is_the_last_day_of_summer_in_Southern_Hemisphere

October 24, 2010September 15, 2016 by Matt Williams

What is Interstellar Space?

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The boundary of what is known, that place known as the great frontier, has always intrigued and enticed us. The mystery of the unknown, the potential for discovery, the fear, the uncertainty; that place that exists just beyond the edge has got it all! At one time, planet Earth contained many such places for explorers, vagabonds and conquerors. But unfortunately, we’ve run out of spaces to label “here be dragons” here at home. Now, humanity must look to the stars to find such places again. These areas, the vast stretches of space that fall between the illuminated regions where stars sit, is what is known as Interstellar Space. It can be the space between stars but also can refer to the space between galaxies.

On the whole, this area of space is defined by its emptiness. That is, there are no stars or planetary bodies in these regions that we know of. That does not mean, however, that there is absolutely nothing there. In fact, interstellar areas do contain quantities of gas, dust, and radiation. In the first two cases, this is what is known as interstellar medium (or ISM), the matter that fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of electromagnetic radiation, is known as the interstellar radiation field. On the whole, the ISM is thought to be made up primarily of plasma (aka. ionized hydrogen gas) because its temperature appears to be high by terrestrial standards.

The nature of the interstellar medium has received the attention of astronomers and scientists over the centuries. The term first appeared in print in the 17th century in the works of Sir Francis Bacon and Robert Boyle, both of whom were referring to the spaces that fell between stars. Before the development of electromagnetic theory, early physicists believed that space must be filled with an invisible “aether” in order for light to pass through it. It was not until the 20th century though that deep photographic imaging and spectroscopy that scientists were able to postulate that matter and gas existed in these regions. The discovery of cosmic waves in 1912 was a further boon, leading to the theory that interstellar space was pervaded by them. With the advent of ultraviolet, x-ray, microwave, and gamma ray detectors, scientists have been able to “see” these kinds of energy at work in interstellar space and confirm their existence.

Many satellites have been launched with the intention of sending back information from interstellar space. These include the Voyager 1 and 2 spacecraft which have cleared the known boundaries of the Solar System and passed into the heliopause. They are expected to continue to operate for the next 25 to 30 years, sending back data on magnetic fields and interstellar particles.

We have written many articles about interstellar space for Universe Today. Here’s an article about deep space, and here’s an article about interstellar space travel.

If you’d like more information on the Interstellar Space, here’s a link to Voyager’s Interstellar Mission Page, and here’s the homepage for Interstellar Science.

We’ve recorded an episode of Astronomy Cast all about Interstellar Travel. Listen here, Episode 145: Interstellar Travel.

Sources:
http://en.wikipedia.org/wiki/Interstellar_space#Interstellar
http://en.wikipedia.org/wiki/Interstellar_medium
http://www.seasky.org/solar-system/interstellar-space.html
http://en.wikipedia.org/wiki/Electromagnetic_radiation
http://en.wikipedia.org/wiki/Heliopause#Heliopause