Galaxy Shapes

Galaxy Shapes
Image credit: NASA/JPL-Caltech/UCLA

Science revealed to us that universe as we know it, is composed of billions of galaxies like our own Milky Way. When you consider how many stars are just in our own galaxy you can get just a small idea how big our universe really is. Despite this astronomers have made great strides in learning more about the galaxies and their different characteristics. One aspect that was defined early was their shapes. Thanks to the work of famous astronomer Edwin Hubble we know that just about any galaxy in the universe will have one of 4 different shapes, spiral, elliptical, lenticular, and irregular.

Spiral galaxies are one of the most familiar galaxy shapes. In fact when most people think of a galaxy, this type of galaxy shape is the first to come to mind. This is because the Milky Way is a prime example of a spiral galaxy. A spiral galaxy looks like a pinwheel. It is basically the nucleus with its different “arms” spiraling outwards. Spiral galaxies can be tight or loose to varying degrees. One important fact about spiral galaxies is that young stars are formed in the outer arms while older stars are found near the center.

The next two types of galaxies are elliptical and lenticular shaped galaxies. These types are the kinds that are the most similar. First they have few or no dust lanes and are largely composed of older mature stars. These types seldom have star forming areas. Of the four galaxy shapes this is the most cohesive and organized.

The final galaxy shape is the irregular galaxy shape. Irregulars have an indeterminate shape. These galaxies are often small and don’t have enough gravitational force to organize into a more regular form. The Hubble telescope has taken images of famous irregular galaxies like the Magellanic Clouds. Irregular galaxies can also be large galaxies that have undergone a major gravitational disturbance.

As you now see the four basic galaxy shapes seem to cover just about every type of galaxy out there. Like any classification of shape there are also subcategories. An interesting observation recently made about the shape of galaxies is the role that their formation plays in determining their shape. It is now thought that galaxies get their shape as they naturally develop, merge with other galaxies or disrupt each other’s path. This is another great mystery as we don’t currently have the technology to plot out the complete paths of galaxies in the universe.

We have written many articles about galaxy shapes for Universe Today. Here’s an article about irregular galaxy, and here’s an article about spiral galaxy.

If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We’ve also recorded an episode of Astronomy Cast about galaxies. Listen here, Episode 97: Galaxies.


How High Do Planes Fly

How High Do Planes Fly
Boeing 747. Image Source:

Have you ever asked how high do planes fly? The answer is easy to understand when you remember how flight for aircraft works. The first thing to know is that air is a fluid just like water. So it works under the same rules. Any object that moves in a fluid is under the influence of four forces, drag, lift, weight, and thrust. The net total has to be positive so that the influence of thrust and lift keeps a plane in the air. Thrust and lift depend on the density of the air. So it is easier to achieve the ideal lift and thrust at higher elevations than lower elevations. So how high a plane flies is not fixed except for the limit of the vacuum of space of where the atmosphere becomes too thin for aerodynamics to work.

Lift and thrust are the main forces that make flight possible. As long as they are greater than weight or drag, plane will fly. Thrust is the forward acceleration produced by a plane’s engine. The less dense the air the more thrust a plane must produce to create the needed lift. The full explanation is pretty complicated but the best way to put is that every plane has a maximum condition it achieves to fly. This maximum is the best possible combination of density, speed, and lift to fly the plane. That is why the height a plane can fly can vary so much. It depends on the needs of the plane.

A good example is commercial turbo jets. Turbo jets fly below the speed of sound. The also weigh a lot. In order to reach optimal flight conditions and fly at speeds convenient enough to make air travel profitable, most commercial planes fly at 30,000 feet. This is high enough that a plane has the least amount of drag and can reach the top speed its engines can produce safely. Supersonic craft like fighter jets and spy planes can fly much higher. This is because they design of the plane makes it easier for the plane to resist drag and produce greater thrust to compensate for the thinner air.

So we see that how high a plane can fly is determined by its use, the drag, the lift, thrust, and weight. We also know that a planes absolute limit will be where air becomes too thin to act like a fluid which is the uppermost level of the atmosphere. Right now scientist are looking to take advantage of this upper level of the atmosphere to help planes fly even faster. However there are still barriers such as friction and engine design.

We have written many articles about airplanes for Universe Today. Here’s an article about the largest airplane, and here’s an article about pictures of airplanes.

If you’d like more info on airplanes, check out these articles from How Stuff Works. Here’s an article about How Airplanes Fly.

We’ve also recorded an entire episode of Astronomy Cast all GPS Navigation. Listen here, Episode 212: GPS Navigation.

How Stuff Works

Solar Disruption Theory

Why Do Planets Orbit the Sun
The Solar System

Solar disruption theory was one of several theories that emerged before the 18th century concerning the formation of the solar system. Solar disruption theory states that the collision of the sun with another stars caused debris to be ejected from its mass and these debris eventually became the planets. This theory was later discarded for the nebula theory of solar system formation. However there are some scientists that propose that it has some merit.

The big question up until the 18th century was how the solar system was born. There were many explanations for why this happen but many were really only conjecture given the tools available to astronomers at the time. The real question was what would be a probable origin under the known laws of physics. The advent of classical mechanics came to prove the nebular theory as the likely theory for the creation of the solar system. The reason was that most other theories could not explain how the planets formed without giving in to the Sun’s gravity and falling in.

A new argument has emerged for a different form of solar disruption theory in this version it answers the idea in a more roundabout way that answers an interesting question. We know that the formation of the solar system itself was volatile but did the Sun and its planets really form in relative isolation from other star emerging in the Nebula? This new theory that emerged in 2004 supposed proposed that the influence of other stars may have influenced the formation of planets in the solar system.

In the meanwhile the main theory stands. We know in the nebular theory that stars are formed from spinning nebulas of gases and cosmic dust. Over time the masses clump together to the point where the mass reaches the level needed for gravity to initiate fusion. The planets are formed from the clumps of debris in the nebular disk that did not fall into the Sun and that they eventually ended up colliding with each other forming planets. Any theory that suggests interference from the gravity fields of other star systems has not been tested yet. It may have merit but we don’t have the technology to test theories on such large scales.

We have written many articles about solar disruption theory for Universe Today. Here are some interesting facts about the Solar System, and here’s an article about the model of the Solar System.

If you’d like more info on the Solar System, check out NASA’s Solar System exploration page, and here’s a link to NASA’s Solar System Simulator.

We’ve also recorded a series of episodes of Astronomy Cast about every planet in the Solar System. Start here, Episode 49: Mercury.


What is a Warm Front?

Warm Front
What is a Warm Front

[/caption]A warm front is the transition zone that marks where a warm air mass starts replacing a cold air mass. Warm fronts tend to move from southwest to southeast. Normally the air behind a warm front is warmer than the air in front of it. Normally when a warm front passes through an area the air will get warmer and more humid. Warm fronts signal significant changes in the weather. Here are some of the weather signs that appear as a warm front passes over a region.

First before the warm front arrives the pressure in area start to steadily decrease and temperatures remain cool. The winds tend to blow south to southeast in the northern hemisphere and north to northeast in the southern hemisphere. The precipitation is normally rain, sleet, or snow. Common cloud types that appear would various types of stratus, cumulus, and nimbus clouds. The dew point also rises steadily

While the front is passing through a region temperatures start to warm rapidly. The atmospheric pressure in the area that was dropping starts to level off. The winds become variable and precipitation turns into a light drizzle. Clouds are mostly stratus type clouds formations. The dew point then starts to level off.

After the warm front passes conditions completely reverse. The atmospheric pressure rises slightly before falling. The temperatures are warmer then they level off. The winds in the northern hemisphere blow south-southwest in the northern hemisphere and north-northwest in the southern hemisphere. Cloudy conditions start to clear with only cumulonimbus and stratus clouds. The dew point rises then levels off.

Knowing about how warm fronts work gives a better understanding of how pressure systems interact with geography to create weather. Looking at warm fronts we learn that they are the transition zone between warm humid air masses and cool, dry air masses. We know that these masses interact in a cycle of rising and falling air that alters the pressure of atmosphere causing changes in weather.

We have written many articles about warm front for Universe Today. Here’s an article about cyclones, and here’s an article about cloud formations.

If you’d like more info on warm front, check out NOAA National Weather Service. 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.


How Does Fog Form?

How Does Fog Form
San Francisco Fog. Image Credit: Wikimedia User, Mila Zinkova

Fog is a natural weather conditions that can cause visibility to become zero. It can cause accidents on normally safe roads and is such a serious weather condition that schools delay the start of the day until the sun burns it off. So how does fog form? First it is important to understand that fog is basically a cloud on the ground. This means like clouds it is a collection of tiny water droplets formed when evaporated water is cooled. The way it is cooled determines how fog is formed.

The first way that fog is formed is by infrared cooling. Infrared cooling happens due to the change of seasons from summer to fall and winter. During the summer the ground absorbs solar radiation. As air passes over it is made warm and moist. When the seasons change this mass of warm moist air collides with the cooler that is now prevalent. This cause is the water vapor in the air mass to condense quickly and fog is formed. This fog is often called radiation fog due to the way it forms. This kind is the most common type of fog. It also happens when an unseasonable day of warm weather combined with high humidity is followed by dropping temperatures

The next way that fog forms is through advection. Advection is wind driven fog formation. In this case warm air is pushed by winds across a cool surface where it condenses into fog. There are also other kinds of fog like hail fog or freezing fog. Each of these conditions is where condensed water droplets are cooled to the point of freezing. There is also fog formed over bodies of water. One type is sea smoke. This is a type of fog that forms when cool air passes over a warm body of water or moist land.

In general we see that fog is formed whenever there is a temperature difference between the ground and the air. When the humidity is high enough and there is enough water vapor or moisture fog is sure to form. However the kind of fog and how long is last and its effects will depends on the different conditions mentioned. One interesting kind of fog actually helps to make snow melt faster.

We have written many related articles for Universe Today. Here’s an article about stratus clouds, and here’s an article about acid rain.

If you’d like more info on fog, check out NOAA National Weather Service website. 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.


Permanent Magnet

Permanent Magnet
Super Magnets, the strongest type of permanent magnets

A permanent magnet is a magnet that does not lose its magnet field. However what makes a magnet permanent? In order to understand this we need to know how magnets work. Magnetism is an aspect of the phenomenon known as the electromagnetic force a fundamental force of the physical universe. Magnetism like its other aspect electricity manifests itself as a field. What makes a magnet is when certain substances and elements are induced with a strong magnetic field. In the case of permanent magnets this field remains over time without weakening.

A permanent magnet is a magnet because of the orientation of its domains. Domains are the small magnetic field inherent in the crystalline structure of ferromagnetic materials. Ferromagnetic materials are the only substances capable of being made into magnets they are normally iron, nickel, or alloys that are made or rare-earth metals. A magnet is created when certain condition cause separate domains in a ferromagnetic item to be all aligned in the same direction. However the method used in most cases weak magnets can only be made. This is normally by direct contact with a naturally magnetic material or by running an electric current through it. However in the case of a field produced by rubbing it against a strong magnet is too weak and will fade over time as the domains return to their original positions.

The main way that permanent magnets are created is by heating a ferromagnetic material to a key high temperature. The temperature is specific to each kind of metal but it has the effect of aligning and “fixing” the domains of the magnet in a permanent position. It is conjectured that this same process inside the Earth is what creates natural permanent magnets.

Permanent magnets are important for their industrial uses especially when it comes to power generation and electric motors. The induction process for turbines and generators needs permanent magnets to turn mechanical motion into energy. They are also important for electric motors in many electronics using the reverse of the induction of electric current to make mechanical energy. As you can see without the permanent magnet we would not be able to take full advantage of the capabilities of electricity in modern devices.

We have written many articles about permanent magnets for Universe Today. Here’s an article about bar magnets, and here’s an article about super magnets.

If you’d like more info on permanent magnets, check out these articles from Hyperphysics and Practical Physics.

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

How Magnets Work

F6 Tornado

F6 Tornado
Tornado in Seymour, Texas

Everyone knows that tornadoes are among nature’s most powerful and destructive phenomenon on land. Also just like other types of storms tornadoes are ranked by strength. The way that tornadoes are ranked is using the Fujita scale. The Fujita scale is a scale that measures the strength of a tornado by the speed of the winds and the amount of the destruction that it causes. The scale is not perfect in that it is hard to directly measure the speeds of the winds and when looking at damage the guidelines are very general and damage becomes indistinguishable after F3.

The Fujita scale is no longer in use since scientists agreed decommission it in favor of the Enhanced Fujita scale, a more nuanced version of the scale that better ranks tornadoes with detailed guidelines concerning wind and destruction patterns. The Fujita scale is still useful to the average person in giving them a general idea of the strength of a tornado. The interesting thing to look for in the Fujita scale is when it reaches F6 tornado. The F6 is a mythical tornado that you would likely only see in movies or hear of in tall tales. It is similar to the magnitude 10 tornado. Early history may have witnessed such phenomena but they have not occurred in modern times due to more settled climates.

The F6 tornado would be the granddaddy of all tornadoes. It would have wind speeds exceeding 300 miles per hour at maximum and would be able to lift houses from their foundations like Dorothy’s Kansas home in the Wizard of Oz. Car would become ballistic missiles able to hurl at tremendous speeds. However; even if such a tornado existed, it would be hard to identify even with an Enhanced Fujita scale. The damage would look mostly the same as an F5 tornado’s damage. It is thought that the more severe damage would be evidenced by specific funnel marks.

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

If you’d like more info on F6 tornadoes, check out amazing articles from:
Tornado Project

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

How Hot is Lava

How Hot is Lava
Carrizozo Lava Flow from Space


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.

NASA Earth Observatory

How Fast Does Light Travel

How Does Light Travel?


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!

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

How Does a Compass Work

How Does a Compass Work
Pocket Compass. Image Credit: Solar Navigator


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.

How Stuff Works