Posted on by Fraser Cain

Sand Storm

Spring Sandstorm Scours China
Spring Sandstorm Scours China

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A sand storm, also known as a dust storm is an atmospheric event when strong winds lift dust from one region and carry it into another. They’re most common in arid, desert regions where there’s little vegetation to hold the topsoil and sand down. Large sand storms can carry dust thousands of kilometers; dust that started in the Arabian desert can be dropped into the Pacific Ocean.

Sand storms get going when there’s a very dry region, without wet soil to hold the particles together. The smallest particles of sand can be pulled out of the ground by the wind, and held in suspension by the wind. It’s thought that static electricity in the storm can cause even more particles to pull out of the ground in addition to the wind effect. In some cases the dust is held low to the ground, but with the right atmospheric conditions, the sand can be carried more than 6 km high in the atmosphere.

Although sand storms are a natural event, it’s believed that poor farming techniques contribute to the problem. As the topsoil is depleted and erodes away by farming and grazing animals, it exposes the underlying sand and dust. This situation led to the huge dust storms of the Dust Bowl in the 1930s in the United States.

A dust storm can be quite a hazard if you get caught in one. The storms can spread over hundreds of kilometers, with driving winds that can be over 40 km/h. The sand can be thick enough to obscure visibility down to a very short distance. The dust can also be a danger to people with asthma and other respiratory illnesses.

Dust storms don’t just happen on Earth, they can also happen on Mars. In fact, dust storms can become so large on Mars they obscure the entire planet. When NASA’s Mariner 9 spacecraft arrived at Mars in 1971, there was a huge dust storm raging. Only the volcano Olympus Mons was visible above the haze of the dust storm. The most recent planet-wide dust storm occurred in 2007, posing a risk to the Mars Exploration Rovers. They rely on sunlight to power their solar panels, but the dust settling on their panels was reducing their power output.

We have written many articles about sand storms for Universe Today. Here’s an article about the black sand beaches, and here are some sandstorm pictures.

If you’d like more info on sandstorms, check out Visible Earth Homepage. 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.

Posted on by Fraser Cain

Transit

Transiting
NASA's Hinode X-ray telescope captured Mercury in transit against the Sun's corona in Nov. 2006. Similar views are possible in H-alpha light. Credit: NASA

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Although the word “transit” can have many meanings, here on Universe Today, we’re talking about astronomical transits. This is where one object in space moves directly in front of another, partly obscuring it from view.

The most famous example of an astronomical transit is a solar eclipse. From our vantage point on Earth, the Moon appears to pass directly in front of the Sun, obscuring it, and darkening the sky. When seen from space, the Moon casts a shadow on the surface of the Earth; only people within that shadowed area actually see the transit.

In order to have a transit, you need to have a closer object, a more distant object, and then an observer. When all three objects are lined up in a straight line, you’ll get a transit. There can be transits of Mercury and Venus across the surface of the Sun, or a transit of Earth across the Sun, seen from Jupiter. We can also see the transit of moons across the surface of their planets. Jupiter often has moons transiting in front of it.

Astronomers use the transit technique to discover extrasolar planets orbiting other stars. When a planet passes in front of a star, it dims the light from the star slightly. And then the star brightens again as the planet moves away. By carefully measuring the brightness of the star, astronomers are able to detect if they have planets orbiting them.

Transits are also helpful for studying the atmospheres of objects in the Solar System. Astronomers discovered that Pluto has a tenuous atmosphere by studying how it dimmed the light from a more distant star. As Pluto began transiting in front of the star, its atmosphere partly obscured the star, changing the amount of light observed. Astronomers were then able to work out the chemicals in Pluto’s atmosphere.

The next transit of Mercury will occur in 2016, and the next transit of Venus is scheduled to occur in 2012.

We have written many articles about astronomical transit for Universe Today. Here’s an article about the transit of Mercury, and here’s an article about the transit of Venus.

If you’d like more info about Astronomical Transit, check out NASA Homepage, and here’s a link to NASA’s Solar System Simulator.

We’ve also recorded related episodes of Astronomy Cast about the Eclipse. Listen here, Episode 160: Eclipses.

Source: Wikipedia

Posted on by Fraser Cain

What Are Tornadoes?

Tornado at Union City, Oklahoma Credit: NOAA Photo Library
Tornado at Union City, Oklahoma Credit: NOAA Photo Library

Also known as a twister, a tornado is a rotating column of air that can cause a tremendous amount of damage on the ground. Tornadoes can very in size from harmless dust devils to devastating twisters with wind speeds greater than 450 km/h.

A tornado looks like a swirling funnel of cloud that stretches from bottom of the clouds down to the ground. Depending on the power of the tornado, there might be a swirling cloud of debris down at the ground, where it’s tearing stuff up. Some tornadoes can look like thin white ropes that stretch from the sky down to the ground, and only destroy a thin patch of ground. Others can be very wide, as much as 4 km across, and leave a trail of destruction for hundreds of kilometers.

Tornadoes appear out of special thunderstorms known as supercells. They contain a region of organized rotation in the atmosphere a few kilometers across. Rainfall within the storm can drag down an area of this rotating atmosphere, to bring it closer to the ground. As it approaches the ground, conservation of momentum causes the wind speed to increase until it’s rotating quickly – this is when tornadoes cause the most damage. After a while the tornado’s source of warm air is choked off, and it dissipates.

When a tornado forms over water, it’s called a waterspout. These can be quite common in the Florida Keys and the northern Adriatic Sea. Most are harmless, like dust devils, but powerful waterspouts can be driven by thunderstorms and be quite dangerous.

Scientists have several scales for measuring the strength and speed of tornadoes. The most well known is the Fujita scale, which ranks tornadoes by the amount of damage they do. A F0 tornado damages trees, but that’s about it, while the most powerful F5 tornado can tear buildings off their foundations. Another scale is known as the TORRO scale, which ranges from T0 to T11. In the United States, 80% of tornadoes are F0, and only 1% are the more violent F4 or F5 twisters.

Although they can form anywhere in the world, tornadoes are mostly found in North America, in a region called Tornado Alley. The United States has the most tornadoes of any country in the world; 4 times as many as the entire continent of Europe. The country gets about 1,200 tornadoes a year.

We have written many articles about the tornado for Universe Today. Here’s an article about the biggest tornado, and here’s an article about how tornadoes are formed.

If you’d like more info on tornadoes, check out the National Oceanic & Atmospheric Administration (NOAA) Homepage. 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.

Posted on by Fraser Cain

Terminator

Geological Period

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No, this isn’t a movie about robots. The terminator is the line that separates day from night on an object lit by a star. You can see evidence of this terminator when you look at the Moon. When we see the Moon, half in light and half in darkness, we’re seeing the terminator line going right down the middle of the Moon.

From our perspective here on Earth, we see the Sun rise from the East, go through the sky and then set again in the West. But if you could see the Earth from space, you would see half the planet is always illuminated, and half the planet is always in shadow. Since the Earth is rotating, we can watch different parts of the planet illuminated, and other parts darkened. The people on the surface of the planet are experiencing the Sun moving through the sky, but really it’s them who are doing the moving.

The location of the terminator depends on the axial tilt of the object. Since the Earth is tilted by 23.5° away from the Sun’s axis, the position of the terminator changes depending on the season. During summer in the northern horizon, the Earth’s north pole never goes into shadow, so the terminator never crosses the pole. And then in winter in the northern horizon, it never comes out of shadow.

If you could orbit the Earth, just above the equator, you would see the terminator line speeding away at approximately 1,600 km/h (1000 miles per hour). Only the fastest supersonic aircraft can match the terminator’s speed. But as you get closer to the poles, the terminator moves more slowly. Eventually at the poles, you can walk faster than the speed of the terminator.

When you see a terminator from afar, it can tell you a lot about a planet or moon. For example, the Earth’s terminator is fuzzy. This means that our planet has a thick atmosphere that scatters the light from the Sun. The Moon, on the other hand, is airless, so its terminator is a crisp line. When you’re standing on the surface of the Moon, it’s either bright or dark, not the in-between twilight that we experience here on Earth.

We have written many articles about the terminator for Universe Today. Here’s an article about why the Sun rises in the East and sets in the West, and here are some Earthrise photos.

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.

Reference:
NASA Earth Observatory

Posted on by Fraser Cain

What Is Terminal Velocity?

Skydiving
Skydiving

The higher you are when you jump, the more it hurts when you hit the ground. That’s because the Earth’s gravity is constantly accelerating you towards its center. But there’s actually a maximum speed you reach, where the acceleration of the Earth’s gravity is balanced by the air resistance of the atmosphere. The maximum speed is called terminal velocity.

The terminal velocity speed changes depending on the weight of the object falling, its surface area and what it’s falling through. For example, a feather doesn’t weigh much and presents a very large surface area to the air as it falls. So its terminal velocity speed is much slower than a rock with the same weight. This is why an ant can fall off a tall building and land unharmed, while a similar fall would kill you. Keep in mind that this process happens in any gas or fluid. So terminal velocity defines the speed that a rock sinks when you drop it in the water.

So, let’s say you’re a skydiver jumping out of an airplane. What’s the fastest speed you’ll go? The terminal velocity of a skydiver in a free-fall position, where they’re falling with their belly towards the Earth is about 195 km/h (122 mph). But they can increase their speed tremendously by orienting their head towards the Earth – diving towards the ground. In this position, the skydiver’s velocity increases to more than 400 km/h.

The world skydiving speed record is held by Joseph Kittinger, who was able to fall at a speed of 988 km/h by orienting his body properly and jumping at high altitude, where there’s less wind resistance.

The gravity of the Earth pulls at you with a constant acceleration of 9.81 meters/second. Without any wind resistance, you’ll fall 9.81 meters/second faster every second. 9.81 meters/second the first second, 19.62 meters/ second in the next second, etc.

The opposing force of the atmosphere is called drag. And the amount of drag force increases approximately proportional to the square of the speed. So if you double your speed, you experience a squaring of the drag force. Since the drag force is going up much more quickly than the constant acceleration, you eventually reach a perfect balance between the force of gravity and the drag force of whatever you’re moving through.

Outside the Earth’s atmosphere, though, there’s no terminal velocity. You’ll just keep on accelerating until you smash into whatever’s pulling on you.

We have written many articles about the terminal velocity for Universe Today. Here’s an article featuring the definition of velocity, and here’s an article about the X-Prize Entrant completing the Drop Test

If you’d like more info on the Terminal Velocity, check out a Lecture on Terminal Velocity, and here’s a link to a NASA article entitled, The Way Things Fall.

We’ve also recorded an entire episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.

Sources:
NASA
Wikipedia
GSU Hyperphysics

Posted on by Fraser Cain

Spacecraft

Space Travel
Atlantis Breaks Through the Clouds

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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

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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 Fraser Cain

Off to Dragon*Con

I’m just doing some final packing and then the wife and I will be flying out to Atlanta to participate in Dragon*Con 2010. This is a gigantic science fiction convention, and we try to represent Astronomy Cast there every year. We’re going to be doing the first ever live show of Astronomy Cast where Pamela and I will actually be together in the same room. Epic!

So if you’re going to be attending Dragon*Con and want to hang out, I should be lurking around the science/skeptic area.

Here’s my schedule so far, but I suspect I’ll be strong-armed into several other panels.

Title: Mystery of Hanny’s Voorwerp
Time: Fri 10:00 pm Location: Crystal Ballroom – Hilton (Length: 1)
Description: Who’s Hanny? What’s a Voorwerp? How’s Hubble involved? See the World Release of the webcomic that explains it all & the 1st Hubble images.

Title: The 2010 Parsec Awards
Time: Sat 04:00 pm Location: Regency V – Hyatt (Length: 2.5)
Description: The Parsec Award is available for original Sci-Fi & Fantasy & Speculative Fiction within the new frontiers of Portable Media.

Title: Astronomy Cast Live!
Time: Sun 01:00 pm Location: 204 – Hilton (Length: 1)
Description: Take a facts-based journey through the cosmos with Dr. Pamela Gay and Fraser Cain

Posted on by Fraser Cain

Trailer for Phil Plait’s Bad Universe

My good friend (and forum co-admin) Phil Plait has been working on a super secret project for a few months. But now the project has been revealed in all its glory… it’s a television show called “Bad Universe“. Phil made the announcement a couple of days ago, but had to remove the video for technical purposes (or perhaps it’s a vast conspiracy). Anyway, the trailer’s back online, so now you can check it out.

Nice work Phil!