Posted on by Fraser Cain

Spacecraft

Space Travel
Atlantis Breaks Through the Clouds

[/caption]

When a vehicle or robot is designed to leave the Earth’s atmosphere and travel through space, we call that a spacecraft. There are many different kinds of spacecraft, such as satellites orbiting the Earth, robots sent to other planets, orbiting space stations, and vehicles sent to the Moon carrying human astronauts.

The harsh environment of space is hard on spacecraft, so they have to be built to tolerate temperature extremes that dip down hundreds of degrees below zero, and then hot enough to boil water. There’s no atmospheric pressure in space, so any spacecraft carrying humans needs a rigid shell that keeps its atmosphere inside. There is a constant stream of radiation from the Sun and outside the Solar System constantly raining down on a spacecraft, damaging components and raising the cancer risk for any human astronauts.

Spacecraft also need components to be able to travel in space. They require a form of propulsion that allows them to change their trajectory. These can range from traditional chemical rockets to the newer ion drives and even nuclear engines. Spacecraft need some kind of power system, solar panel arrays or nuclear generators. They need a communications system to send and receive signals from Earth. They require an attitude control system, to keep their instruments pointed in the right directions. And finally, they need the specific components to carry out their mission. In the case of the Apollo capsules, these spacecrafts’ mission was to carry NASA astronauts to and from the Moon safely. These means they needed life support systems, navigation computers, and landing equipment. A spacecraft designed to orbit Jupiter will require different components to a spacecraft designed to land on the surface of Venus.

The first spacecraft – the first object to ever leave the Earth’s atmosphere and orbit the planet – was the Soviet satellite Sputnik 1. It launched on October 4th, 1957. The space age began, and many other spacecraft launches followed. The first human to orbit the Earth was Yuri Gagarin, who was carried to space aboard a Soviet rocket on April 12, 1961. The first spacecraft to travel to the Moon was Luna-2, which crashed into the Moon on September 12, 1959. The first spacecraft to safely carry humans to the surface of the Moon was the Apollo 11 mission, which landed on July 20, 1969.

We have written many articles about the spacecraft for Universe Today. Here’s an article about spacecraft propulsion, and here’s an article about the manned spacecraft of China.

If you’d like more information on spacecrafts, here’s a link to NASA’s Official space shuttle page, and here’s the homepage for NASA’s Human Spaceflight.

We’ve recorded an episode of Astronomy Cast all about the space shuttle. Listen here, Episode 127: The US Space Shuttle.

Source: Wikipedia

Posted on by Fraser Cain

Voyager 2

Voyager 2 Mission
Voyager 2 Launch

[/caption]

Voyager 2 is easily the most famous spacecraft sent from Earth to explore other planets. Launched on August 20, 1977, Voyager visited Jupiter and Saturn, and is the only spacecraft to have ever made a flyby of the outer planets Uranus and Neptune. It flew past Neptune in 1989, but it’s still functioning and communicating with Earth.

Voyager 2 and its twin spacecraft Voyager 1 were built at NASA’s Jet Propulsion Lab in Pasadena, California. The two spacecraft were built with identical components, but launched on slightly different trajectories. Voyager 2 took advantage of a rare alignment of the planets so that it could use a gravity assisting boost as it flew past each one. The increased velocity from Jupiter would help it reach Saturn, Saturn helped it get to Uranus and then to Neptune.

It made its closest approach to Jupiter on July 9, 1979, passing within 570,000 km of the planet’s cloud tops. It captured some of the first, highest resolution images of Jupiter’s moons, showing volcanism on Io, and cracks in the icy surface of Europa. Astronomers now suspect that Europa’s surface hides a vast ocean of water ice.

Voyager 2 then went on to visit Saturn on August 26, 1981, and then onto Uranus on January 24, 1986. This was the first time a spacecraft had ever encountered Uranus, and captured images of the planet close up. Voyager studied Uranus’ rings, and discovered several new moons orbiting the planet. Voyager 2 made its final planetary visit with Neptune on August 25, 1989. Here the spacecraft discovered the planet’s “Great Dark Spot”, and discovered more new moons.

Voyager 2 is now considered an interstellar mission. This means that it has enough velocity to escape the Solar System and travel to another star. Of course, at its current speed, it would take hundreds of thousands of years to reach even the closest star. Scientists think that the spacecraft will continue transmitting radio signals until at least 2025, almost 50 years after it was launched.

We have written many articles about Voyager 2 for Universe Today. Here’s an article about NASA’s diagnosed problems with Voyager 2, and here are some Voyager 2 pictures.

If you’d like more information on the Voyager 2 mission, here’s a link to Voyager’s Interstellar Mission Homepage, and here’s the homepage for NASA’s Voyager Mission Website.

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

Source: NASA

Posted on by Jerry Coffey

What Is Atomic Mass

Faraday's Constant

[/caption]

The answer to ‘what is atomic mass’ is this: the total mass of the protons, neutrons, and electrons in a single atom when it is at rest. This is not to be associated or mistaken for atomic weight. Atomic mass is measured by mass spectrometry. You can figure the molecular mass of an compound by adding the atomic mass of its atoms.

Until the 1960’s chemists and physicists used different atomic mass scales. Chemists used a scale that showed that the natural mixture of oxygen isotopes had an atomic mass 16. Physicists assigned 16 to the atomic mass of the most common oxygen isotope. Problems and inconsistencies arose because oxygen 17 and oxygen 18 are also present in natural oxygen. This created two different tables of atomic mass. A unified scale based on carbon-12 is used to meet the physicists’ need to base the scale on a pure isotope and is numerically close to the chemists’ scale.

Standard atomic weight is the average relative atomic mass of an element in the crust of Earth and its atmosphere. This is what is included in standard periodic tables. Atomic weight is being phased out slowly and being replaced by relative atomic mass. This shift in wording dates back to the 1960’s. It has been the source of much debate largely surrounding the adoption of the unified atomic mass unit and the realization that ‘weight’ can be an inappropriate term. Atomic weight is different from atomic mass in that it refers to the most abundant isotope in an element and atomic mass directly addresses a single atom or isotope.

Atomic mass and standard atomic weight can be so close, in elements with a single dominant isotope, that there is little difference when considering bulk calculations. Large variations can occur in elements with many common isotopes. Both have their place in science today. With advances in our knowledge, even these terms may become obsolete in the future.

We have written many articles about atomic mass for Universe Today. Here’s an article about the atomic nucleus, and here’s an article about the atomic models.

If you’d like more info on the Atomic Mass, check out NASA’s Article on Analyzing Tiny Samples, and here’s a link to NASA’s Article about Atoms, Elements, and Isotopes.

We’ve also recorded an entire episode of Astronomy Cast all about the Atom. Listen here, Episode 164: Inside the Atom.

Sources:
Wikipedia
Windows to Universe
NDT Resource Center

Posted on by Jerry Coffey

What Is Atmospheric Pressure

Thermosphere
The Moon viewed from Earth's thermosphere. Credit: NASA

[/caption]

Just answering the question ‘what is atmospheric pressure?’ is not enough to give a full understanding of its importance. By definition atmospheric pressure is ‘force per unit area exerted against a surface by the weight of air above that surface’. Atmospheric pressure is closely related to the hydrostatic pressure caused by the weight of air above the measurement point. The term standard atmosphere is used to express the pressure in a system(hydraulics and pneumatics) and is equal to 101.325 kPa. Other equivalent units are 760 mmHg and 1013.25 millibars.

Mean sea level pressure (MSLP) is the pressure at sea level. This is the pressure normally given in weather reports. When home barometers are set to match local weather reports, they will measure pressure reduced to sea level, not your local atmospheric pressure. The reduction to sea level means that the normal range of fluctuations in pressure are the same for everyone.

Atmospheric pressure is important in altimeter settings for flight. A altimeter can be set for QNH or QFE. Both are a method of reducing atmospheric pressure to sea level, but they differ slightly. QNH will get the altimeter to show elevation at the airfield and altitude above the air field. QFE will set the altimeter to read zero for reference when at a particular airfield. QNH is transmitted around the world in millibars, except in the United States and Canada . These two countries use inches (or hundredths of an inch) of mercury.

Atmospheric pressure is often measured with a mercury barometer; however, since mercury is not a substance that humans commonly come in contact with, water often provides a more intuitive way to visualize the pressure of one atmosphere. One atmosphere is the amount of pressure that can lift water approximately 10.3m. A diver who is 10.3m underwater experiences a pressure of about 2 atmospheres (1of air plus 1of water). Low pressures like natural gas lines can be expressed in inches of water(w.c). A typical home gas appliance is rated for a maximum of 14 w.c.(about 0.034 atmosphere).

You can see that understanding ‘what is atmospheric pressure’ is just the tip of the iceberg. Once you have the definition in mind, it really comes together when you see the wide variety of applications.

We have written many articles about atmospheric pressure for Universe Today. Here’s an article about atmospheric pressure, and here’s an article about air pressure.

If you’d like more info on the Atmospheric Pressure, check out NASA’s Discussion Video on Atmospheric Pressure, and here’s a link to How Atmospheric Pressure Affects the Weather?

We’ve also recorded an entire episode of Astronomy Cast all about the Atmospheric Pressure. Listen here, Episode 151: Atmospheres.

Posted on by Jerry Coffey

What Is An Electron

Faraday's Constant

[/caption]

What is an electron? Easily put, an electron is a subatomic particle that carries a negative electric charge. There are no known components, so it is believed to be an elementary particle(basic building block of the universe). The mass of an electron is 1/1836 of its proton. Electrons have an antiparticle called a positron. Positrons are identical to electrons except that all of its properties are the exact opposite. When electrons and positrons collide, they can be destroyed and will produce a pair (or more) of gamma ray photons. Electrons have gravitational, electromagnetic, and weak interactions.

In 1913, Niels Bohr postulated that electrons resided in quantized energy states, with the energy determined by the spin(angular momentum)of the electron’s orbits and that the electrons could move between these orbits by the emission or absorption of photons. These orbits explained the spectral lines of the hydrogen atom. The Bohr model failed to account for the relative intensities of the spectral lines and it was unsuccessful in explaining the spectra of more complex atom. Gilbert Lewis proposed in 1916 that a ‘covalent bond’ between two atoms is maintained by a pair of shared electrons. In 1919, Irving Langmuir improved on Lewis’ static model and suggested that all electrons were distributed in successive “concentric(nearly) spherical shells, all of equal thickness”. The shells were divided into a number of cells containing one pair of electrons. This model was able to qualitatively explain the chemical properties of all elements in the periodic table.

The invariant mass of an electron is 9.109×10-31 or 5.489×10-4 of the atomic mass unit. According to Einstein’s principle of mass-energy equivalence, this mass corresponds to a rest energy of .511MeV. Electrons have an electric charge of -1.602×10 coulomb. This a standard unit of charge for subatomic particles. The electron charge is identical to the charge of a proton. In addition to spin, the electron has an intrinsic magnetic moment along its spin axis. It is approximately equal to one Bohr magneton. The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as helicity. Observing a single electron shows the upper limit of the particle’s radius is 10-22 meters. Some elementary particles decay into less massive particles. But an electron is thought to be stable on the grounds that it is the least massive particle with non-zero electric charge.

Understanding what is an electron is to begin to understand the basic building blocks of the universe. A very elementary understanding, but a building block to great scientific thought.

We have written many articles about the electron for Universe Today. Here’s an article about the Electron Cloud Model, and here’s an article about the charge of electron.

If you’d like more info on the Electron, check out the History of the Electron Page, and here’s a link to the article about Killer Electrons.

We’ve also recorded an entire episode of Astronomy Cast all about the Composition of the Atom. Listen here, Episode 164: Inside the Atom.

Posted on by Tega Jessa

What Are Clouds Made Of?

Clouds

When we think of clouds we think of those white cotton ball masses in the air. What we don’t really think about is what are clouds made of. We all know about the water cycle in some form. We know that clouds are created from the water that evaporates from various lakes, rivers, and oceans. We also know that at some time this evaporated water becomes rain and starts the cycle all over again.

However there are important questions about clouds we overlook. First, how are clouds visible if water vapor is normally supposed to be invisible like air or at least dissipate quickly after the first gush of steam? Second, why do clouds last so long in their different forms? Finally, what gives clouds their white or grey colors? As you can see there is a lot we take for granted in our understanding of clouds and how they are formed.

We know that clouds are made of water vapor, what we don’t know or at least forget is the important role that condensation plays in making clouds visible. For the most part water vapor is invisible. This is proven by the fact that the air we breathe regularly has some water vapor as part of its composition. However we don’t see it since its apart of the air. Condensation is what makes water vapor visible.

Basically high temperatures excite water molecules until they change from a liquid state to a gaseous one. However lower temperatures can cause enough water vapor to condense back into liquid form. This small amount stays as very small droplets that can stay suspended in the air mostly thanks to small dust particles that they attach themselves to.

It is pretty much the same way you see small bits of glitter suspended in clear glue. The drops are small enough to stay trapped in the air until condensation reaches a point of no return making rain. One result of this is that light becomes reflected and refracted. This is what makes clouds visible.

Now if you think about it we also just answered the second question about why clouds last so long. You may understand the first explanation because you can see your breath on a cold day. However after a while depending on the weather you notice that later in the day you can no longer see your breath. Clouds are visible because of colder temperatures in the upper atmosphere.

You have to remember that in the upper reaches of the atmosphere that the temperatures are much colder. This means that water vapor once condensed can no longer return fully to its gas state. Since temperatures don’t change in this region clouds are able to keep shape longer.

Finally, clouds have color. Some are white, some are grey, and in special circumstances such as major storms can have weird colors like green or red. This goes back to refraction. Most color that we can see is visible because are eyes perceive how objects absorb or reflect certain wavelengths of light. The white colors of clouds come from the condensed water vapor having a high reflective quality.

When all wavelengths of light are reflected back you see white. The grey color comes from seeing clouds from beneath. White clouds are white if you notice, on sunny days. This is because you can see the sunlight directly hitting them and see that light almost completely reflected back. On cloudy days most sunlight is blocked by the translucent and refractive quality of cloud cover. This makes clouds appear darker in color as part of the light has been uniformly absorbed.

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

If you’d like more info on clouds, check out an article aboutClouds. And here’s a link to NASA Spaceplace Page about Clouds.

We’ve also recorded an episode of Astronomy Cast all about the Atmosphere. Listen here, Episode 151: Atmospheres.

Posted on by Tega Jessa

What are Electrons

Fine Structure Constant

[/caption]

If you have heard of electrons you know that they have something to do with electricity and atoms. If so you are mostly right in describing what are electrons. Electrons are the subatomic particles that orbit the nucleus of an atom. They are generally negative in charge and are much smaller than the nucleus of the atom. If you wanted a proper size comparison the size of the earth in comparison to the sun would be a pretty close visualization.

Electrons are known to fall into orbits or energy levels. These orbits are not visible paths like the orbit of a planet or celestial body. The reason is that atoms are notoriously small and the best microscopes can only view so much of atoms at that scale. Even if we could view electrons they would move too fast for the human eye. As a matter of fact scientists still can’t calculate the exact position of electrons. They can only estimate their locations. That is why the modern model of the atoms has an electron cloud surrounding the nucleus of an atom instead of a defined system of electrons in concentric orbits.

Electrons are also important for the bonding of individual atoms together. With out this bonding force between atoms matter would not be able to interact in the many reactions and forms we see every day. This interaction between the outer electron layers of an atom is call atomic bonding. It can occur in two forms. One is covalent bonding where atoms share electrons in their outer orbits. The other is ionic bonding where an atom gives up electrons to another atom. In either case bonding must meet specific rules. We won’t go into great detail, but each electron orbit or electron energy level can only hold so many electrons. Atoms can only bond if there is room to share or receive extra electrons on the outermost orbit of the atom.

Electrons are also important to electricity. Electricity is basically the exchange of electrons in a stream called a current through a conducting medium. In most cases the medium is an acid, metal, or similar conductor. In the case of static electricity, a stream of electrons travels through the medium of air.

The understanding of the electron has allowed for a better understanding of some of the most important forces in our universe such as the electromagnetic force. Understanding its workings has allowed scientist to work out concepts such potential difference and the relationship between electrical and magnetic fields.

We have written many articles about electrons for Universe Today. Here’s an article about the atom diagram, and here’s an article about the electron cloud model.

If you’d like more info on Electrons, check out the Discussion about Electrons, and here’s a link to the History of the Electron Article.

We’ve also recorded an entire episode of Astronomy Cast all about the Atom. Listen here, Episode 164: Inside the Atom.

Sources:
Wikipedia
Windows to Universe

Posted on by Jerry Coffey

What Is A Continent

Map of Earth
Map of Earth

[/caption]
You know that there are 7 continents(6 if you were taught geography in Europe) right now, but do you really know the definition of what is a continent? There are many different, and confusing definitions of what a continent is. The most widely accepted one says that a continent is defined as a large, continuous, discrete mass of land, ideally separated by an expanse of water. This definition somewhat confuses things. Many of the current continents are not discrete landmasses separated by water. The word large leads to arbitrary classification: Greenland, with a surface area of 2,166,086 km2 is considered the world’s largest island, but Australia with a land mass of 7,617,930 km2 is a continent. The qualification that each be a continuous landmass is disregarded because of the inclusion of the continental shelf and oceanic islands and is contradicted by classifying North and South America and Asia and Africa as continents, without a natural separation by water. This idea continues if the land mass of Europe and Asia is considered as two continents. Also, the Earth’s major landmasses are surrounded by one, continuous World ocean that has been divided into a number of principal ‘oceans’ by the land masses themselves and various other geographic criteria.

The number of continents has changed throughout the evolution of the Earth. Plate tectonics and continental drift have forced changes on continental composition. The planet began with one single land mass(the Mesezoic Era). This continent was not suddenly there. It was the result of partially solidified magma being smashed together by plate tectonics and continental drift. Those forces remain at work today.

To further confuse things, different parts of the world teach different versions of the continents. The seven-continent model is usually taught in China and most English speaking countries. A six continent model combining Europe and Asia is preferred by the geographic community, the former parts of the USSR, and Japan. Another six continent model combining North and South America is taught in Latin America and most of Europe.
The answer to ‘what is a continent’ is more by convention than strict definition. Hopefully, this will help to clear some of the confusion that you had before you started reading this article.

We have written many articles about the continents for Universe Today. Here’s an article about the biggest continent, and here’s an article about the continental drift theory.

If you’d like more info on Earth’s continents, 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.

Source: Wikipedia

Posted on by Jerry Coffey

Is There Life On Other Planets

Temperature of Mars
What is the Temperature of Mars? Image credit: NASA/JPL

[/caption]

Is there life on other planets? That has been a question raised from the early beginnings of science fiction. The notion was scoffed at as pure mind play for dreamers and the occasional grifter selling rides to the Moon. At least it was until we were able to reach into space and discover new facts and gather new intel.

The possibility of life on Mars(outside sci-fi books) had been proposed as early as the 1950’s, but there was no real way to prove or disprove the theory until the launch of Mariner 4 in 1965. The spacecraft was able to return the first photographs of the planet’s surface. The news was all bad for those who had hoped for signs of life on the planet. The surface was too extreme and desolate for any type of known life form. The Voyager probes found radiolabeled carbon dioxide, but no organic molecules. Those results give mixed signals and are inconclusive at best. The results have been used to support the possibility of a microorganism named Gillevinia straata.

The Phoenix lander touched down on the Martian surface in May of 2008. The lander dug a trench on the area of the northern pole. No bacteria was found but the samples did contain bound water and carbon dioxide. The most positive evidence of life in the Martian past are meteorites from the planet. 34 exist and 3 show signs of microscopic fossilized bacteria.

Another viable possibility for life on other planets would be those similar to Gliese 581c. These planets are within the habitable zone(for human life) of their main sequence star. These planets appear to have a temperature that would allow liquid water and atmosphere’s that seem spectroscopically close to Earth’s. The information that is needed would detail the greenhouse effect on these planets. If that was available, we would be able to determine suitability for human life.

All of our efforts to answer the question ‘Is there life on other planets?’ are based on finding life that is similar to that on Earth. That is a typically arrogant line of research. Where is it written that the Earth type of life form is pervasive?

We have written many articles about the possibility of life on other planets for Universe Today. Here’s an article about the life on other planets, and here’s an article about life on Mars.

If you’d like more info on the search for life on other planets, check out the NASA Astrobiology Institute Homepage, and here’s a link to NASA Planet Quest: Finding Life.

We’ve also recorded an entire episode of Astronomy Cast all about the Future of Astronomy. Listen here, Episode 188: The Future of Astronomy.

Posted on by Jerry Coffey

First Quarter Moon

Flying Across the Moon
Flying Across the Moon

[/caption]

The first quarter moon is actually the third phase of the moon each cycle. In the Northern Hemisphere during this phase, the right hand 50% of the moon is visible during the afternoon and the early part of the night. In the Southern Hemisphere the left hand 50% of the moon can be seen. This lunar phase follows the new moon and the waxing crescent.

A lunar phase is the appearance of an illuminated portion of the moon as seen by an observer. For this article the observer is always on Earth. The lunar phases vary in a definite cycle as the moon orbits the Earth. The phases change based on the changing relative positions of the Earth, moon, and Sun. Half of the moon’s surface is always illuminated by the Sun, but the portion of the illuminated hemisphere that is visible to an observer can vary from 100%(full moon) to 0%(new moon). The only exception is during a lunar eclipse. The boundary between the light and dark portions of the moon is called the terminator.

There are 8 moon phases. These phases are: new moon, waxing crescent, first quarter moon, waxing gibbous, full moon, waning gibbous, last quarter moon, and waning crescent. The phases progress in the same manner each month. Earlier, it was mentioned that the lunar phase depends on the position of the Earth, moon, and Sun. During the new moon the Earth and Sun are on the opposite side of the moon. During the full moon the Earth and Sun are on the same sides of the Moon. The occasions when the Earth, Sun, and moon are in a straight line(new and full moon) are called syzygies.

When the moon passes between Earth and the Sun during a new moon, you might think that its shadow would cause a solar eclipse. On the other hand, you might think that during a full moon the Earth’s shadow would cause a lunar eclipse. The plane of the moon’s orbit around the Earth is tilted by about five degrees compared to the plane of Earth’s orbit around the Sun(called the ecliptic plane). This tilt prevents monthly eclipses. An eclipse can only occur when the moon is either new or full, but it also has to be positioned near the intersection of the Earth’s orbital plane about the Sun and the Moon’s orbit plane about the Earth, so there are between four and seven eclipses in a calendar year.

The first quarter moon is only one of eight lunar phases. You should research them all for a better understanding of the Earth/Moon system.

We have written many articles about the phases of the moon for Universe Today. Here’s an article about the 8 phases of the moon, and here’s an article about the moon phases for 2010.

If you’d like more info on the Moon, check out NASA’s Solar System Exploration Guide on the Moon, and here’s a link to NASA’s Lunar and Planetary Science page.

We’ve also recorded an entire episode of Astronomy Cast all about the Moon. Listen here, Episode 113: The Moon, Part 1.

References:
http://spaceplace.nasa.gov/en/kids/phonedrmarc/2004_march.shtml
http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question3.html