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Here you can watch video lectures on astronomy topics. Watch one of 29 individual playlists, or use the Wikimap to find similar topics.

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Articles related to: Io  Read article

1. Charon  Read article

Pluto's satellite Charon is half the size of Pluto itself. The ratio between the planet and its moon is the smallest in the solar system. Pluto rotates in 6.4 days, and the orbital period of Charon is the same number, 6.4 days. They are in a synchronous orbit and so always face each other. The d...

2. Gas Giant Composition  Read article

The chemical composition of the giant planets overall is similar to that of the Sun, roughly three quarters hydrogen by mass and one quarter helium by mass. How do we know this? The density of the gas giant planets gives us a good indication of their chemical composition. For instance, the terres...

3. Moons of Jupiter  Read article

Jupiter has four large moons over 3,000 kilometers in diameter. In increasing order of size these are: Europa, Io, Callisto, and Ganymede. These are called the Galilean satellite because they were discovered by Galileo Galilei with his newly found telescope. The discovery of the Galilean moons wa...

4. Density  Read article

In simple big bang models, that is models without a cosmological constant, the critical density of matter is the density needed to just overcome the expansion so that the universe continues to expand but at an ever decreasing rate. It’s defined mathematically as three times the Hubble constant squa...

5. Standard Solar Model  Read article

Knowing the size, composition, and energy source of the Sun, astronomers can calculate the physical conditions at any point within its volume. This is called the standard solar model. Fusion occurs within the core, the inner quarter of the Sun’s radius. The temperature at the very center is fifte...

6. Density of Interstellar Space  Read article

The complex processes of star birth and death and the recycling of gas means that the interstellar medium, the space between stars, is not absolutely empty. The air you are breathing has a density of about one kilogram per cubic meter and has ten to the power twenty-five particles per cubic meter a...

7. Europa  Read article

Jupiter's Europa is one of the Galilean satellites. At 3,100 kilometers in diameter it's similar in size to Io and similar to the Earth's moon. Europa looks completely different from Earth's moon however. It has an uncratered, bright surface of frozen water. In 1996 the Galileo space probe took ...

8. Neutron Star  Read article

In 1934 American astronomers Walter Baade and Fritz Zwicky speculated that the result of a supernova explosion might be a formation of what they called a neutron star. If the burned out core of a massive star is more than 1.4 times the mass of the Sun, degeneracy pressure of the electrons is not su...

9. Callisto  Read article

Jupiter's Callisto is the third largest moon in the solar system behind Jupiter's Ganymede and Saturn's Titan. It is similar is size to the planet Mercury. Callisto is the outermost of the four Galilean satellites, and it has an orbital period around Jupiter of nearly seventeen days. Galileo used...

10. Degenerate Matter  Read article

The physical state inside a white dwarf is extraordinary. The density is in the range of 108 to 1011 kilograms per cubic meter. A teaspoon of white dwarf material brought back to the Earth would weigh as much as an elephant. At these densities and temperatures electrons move nearly at the speed o...