This category contains 189 posts

The Exosphere

This is a picture which shows the Earth, its atmosphere (the clouds are likely in the troposphere and stratosphere), the limb of the Earth (the dark blue curve/edge which is the mesosphere and thermosphere), and the dark blue to black region of space (where our exosphere extends out to…). Image courtesy of NASA Very high … Continue reading

The Plasma State

Plasma: the negatively charged electrons (yellow) are freely streaming through the positively charged ions (blue). General Atomics   Plasma is known as the fourth state of matter (the first three states being solid, liquid and gas). Matter in ordinary conditions on Earth has electrons that orbit around the atomic nucleus. The electrons are bound to … Continue reading


Crystals of the mineral Pyrite from Peru Courtesy of Corel   Solid is one of the four common states of matter. The three others are gas, liquid, and plasma. There are also some other exotic states of matter that have been discovered in recent years. Unlike liquids and gases, solids have definite shapes. If you … Continue reading


Milk is a typical liquid. A liquid takes on the shape of the container it is in; in this case a glass. Liquids have a distinct boundary called a “free surface”; in this case, near the top of the glass where the milk meets the air above it. Image courtesy of Corel Corporation.     … Continue reading

Density Definition Page

This image shows a pool ball floating on liquid mercury. A pool ball is fairly heavy for its size, but you can see it floats on, or is less dense, than liquid mercury.     Density is a measure of how much mass is contained in a given unit volume (density = mass/volume). It is … Continue reading


This is a drawing of what the surface of a comet might look like. NASA/NSSDC, Tom Herbst, Max-Planck-Institut fuer Astronomie, Heidelberg, Doug Hamilton, Max-Planck-Institut fuer Kernphysik, Heidelberg, Hermann Boehnhardt, Universitaets-Sternewarte, Muenchen, and Jose Luis Ortiz Moreno, Instituto de Astrofisica de   Sublimation is an unusual change of state. We are all familiar with evaporation, the … Continue reading


This is a photo of the crashing waves of the ocean. Because the ocean holds so much of the Earth’s water, it is the greatest source of evaporated water to the atmosphere. Corel Photography     One process which transfers water from the ground back to the atmosphere is evaporation. Evaporation is when water passes … Continue reading

Changes of State: Solids, Liquids, and Gases

Water as a liquid, solid and gas. Click on image for full size L.Gardiner/Windows to the Universe   Any substance, called matter, can exist as a solid material, liquid, or gas. These three different forms are called states. Matter can change its state when heated. As a solid, matter has a fixed volume and shape … Continue reading


  The gas inside this balloon pushes outward in all directions. That push is called pressure. The pressure makes the rubber stretch, causing the balloon to inflate. Image courtesy of the University Corporation for Atmospheric Research.     Gas is one of the four common states of matter. The three others are liquid, solid, and … Continue reading

The Thermosphere

  This is an image of the space shuttle as it is orbiting around the Earth. The space shuttle orbits in the thermosphere of the Earth. Image from: Courtesy of NASA   The thermosphere is a layer of Earth’s atmosphere. The thermosphere is directly above the mesosphere and below the exosphere. It extends from about … Continue reading

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