Advertisement. EnchantedLearning.com is a user-supported site. As a bonus, site members have access to a banner-ad-free version of the site, with print-friendly pages.Click here to learn more. (Already a member? The Planets (plus the Dwarf Planet Pluto) Our solar system consists of the sun, eight planets, moons, many dwarf planets (or plutoids), an asteroid belt, comets, meteors, and others. The eight planets that orbit the sun are (in order from the sun): Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Easy ways to remember the order of the planets (plus Pluto) are the mnemonics: "My Very Excellent Mother Just Sent Us Nine Pizzas" and "My Very Easy Method Just Simplifies Us Naming Planets" The first letter of each of these words represents a planet - in the correct order. The largest planet is Jupiter. The inner planets are: Mercury, Venus, Earth, and Mars. Generally, the farther from the Sun, the cooler the planet. Density of the Planets The Earth is the densest planet.
Related: 0006 Understand Earth in the solar system and universe.
What Is a Planet?While many people can point to a picture of Jupiter or Saturn and call it a "planet," the definition of this word is much more subtle and has changed over time. Many astronomers decided on a new definition in 2006 after the discovery of several worlds at the fringes of the solar system — a decision that remains controversial. The International Astronomical Union defined a planet as an object that: orbits the sun has sufficient mass to be round, or nearly round is not a satellite (moon) of another object has removed debris and small objects from the area around its orbit The IAU also created a new classification, "dwarf planet," which is an object that meets planetary criteria except that it has not cleared debris from its orbital neighborhood. This definition meant that Pluto — considered a planet at the time — was demoted and reclassified as a dwarf planet. Planetary history The term "planet" originally comes from the Greek word for "wanderer." Discovery of more worlds
The Moon - Zoom AstronomyThe moon is Earth's only natural satellite. The moon is a cold, dry orb whose surface is studded with craters and strewn with rocks and dust (called regolith). The moon has no atmosphere. Recent lunar missions indicate that there might be some frozen ice at the poles. The same side of the moon always faces the Earth. If you were standing on the moon, the sky would always appear dark, even during the daytime. The moon is about 238,900 miles (384,000 km) from Earth on average. The moon revolves around the Earth in about one month (27 days 8 hours). The Moon's orbit is expanding over time as it slows down (the Earth is also slowing down as it loses energy). SAROS The saros is the roughly 18-year periodic cycle of the Earth-Moon-Sun system. The moon's diameter is 2,159 miles (3,474 km), 27% of the diameter of the Earth (a bit over a quarter of the Earth's diameter). The moon's mass is (7.35 x 10 22 kg), about 1/81 of the Earth's mass. The moon's density is 3340 kg/m 3. MOON OR DOUBLE PLANET?
Sun Facts - Interesting Facts about the Sun (Sol)The Sun or Sol, is the star at the centre of our solar system and is responsible for the Earth’s climate and weather. The Sun is an almost perfect sphere with a difference of just 10km in diameter between the poles and the equator. The average radius of the Sun is 695,508 km (109.2 x that of the Earth) of which 20–25% is the core. Star Profile Age: 4.6 Billion YearsType: Yellow Dwarf (G2V)Diameter: 1,392,684 kmCircumference at Equator: 4,370,005.6 kmMass: 1,989,100,000,000,000,000,000 billion kg (333,060 x Earth)Surface Temperature: 5500 °C Size of the Sun Facts about the Sun One million Earths could fit inside the Sun: If a hollow Sun was filled up with spherical Earths then around 960,000 would fit inside. Eventually, the Sun will consume the Earth: When all the Hydrogen has been burned, the Sun will continue for about 130 million more years, burning Helium, during which time it will expand to the point that it will engulf Mercury and Venus and the Earth. Satellites
Retrograde and prograde motionThis article is about retrograde motions of celestial bodies relative to a gravitationally central object. For the apparent motion as seen from a particular vantage point, see Apparent retrograde motion. Retrograde orbit: the satellite (red) orbits in the direction opposite to the rotation of its primary (blue/black) Formation of celestial systems When a galaxy or a planetary system forms, its material takes the shape of a disk. Orbital parameters Inclination Axial tilt Planets All eight planets in the Solar System orbit the Sun in the direction that the Sun is rotating, which is counterclockwise when viewed from above the Sun's north pole. Dwarf planets Earth's atmosphere Retrograde motion, or retrogression, within the Earth's atmosphere refers to weather systems which move from east to west through the Westerlies or from west to east through the Trade wind easterlies. Moons and rings The orange moon is orbiting in the opposite direction. 
Evidence of cosmic inflation expands universe understandingGWEN IFILL: It’s a mind-boggling concept: Our cosmos expanded from almost nothing to its first huge growth spurt in just a trillionth of a trillionth of a trillionth of a second. And that was after the Big Bang. Scientists said they confirmed that theory by using this telescope at the South Pole to look at the oldest light detectable. The light reveals patterns and skewed light waves, shown here in red and blue, that were created by gravitational ripples during the — this incredible expansion known as cosmic inflation. Sean Carroll is a physicist, cosmologist and author at the California Institute of Technology, and he joins us now to explain all of this. And we need your explanation. SEAN CARROLL, California Institute of Technology: Well, it is. The term cosmic inflation was coined around 1980, when the ordinary economic inflation was also very much in the news. For example, it looks similar, it looks smooth all over the place. SEAN CARROLL: Well, it’s very similar.
Big Bang TheoryGalaxies, Galaxy Information, Galaxy Facts, News, Photos -- National GeographicGalaxies are sprawling space systems composed of dust, gas, and countless stars. The number of galaxies cannot be counted—the observable universe alone may contain 100 billion. Some of these distant systems are similar to our own Milky Way galaxy, while others are quite different. Galaxies with less than a billion stars are considered "small galaxies." In our own galaxy, the sun is just one of about 100 billion stars. Galaxies are classified into three main types: spiral galaxies, elliptical galaxies, and irregular galaxies. Spiral galaxies, such as the Milky Way, consist of a flat disk with a bulging center and surrounding spiral arms. This spinning motion, at speeds of hundreds of kilometers per second, may cause matter in the disk to take on a distinctive spiral shape like a cosmic pinwheel. Older stars reside in the bulge at the center of the galactic disk. Elliptical galaxies are shaped as their name suggests. Galaxies that are not spiral or elliptical are called irregular galaxies.
life cycle of starTypes of Stars by Size, Color and Life CycleLearn to identify the different sizes and colors of stars and how they relate to the star life cycle. In this lesson, we'll talk about spectral classification, how many stars there are of each type and the approximate color of the different classes of stars. Explore our library of over 10,000 lessons You now have full access to our lessons and courses, watch the lesson now or keep exploring. You've watched a video! You took a quiz! You just finished your first lesson. You're making great progress. You've learned so much, but only scratched the surface. Getting a perfect score on a quiz is how you gain course progress. You're getting the hang of this! Look how far you've come! Keep clicking that 'next lesson' button whenever you finish a lesson and its quiz. You're 25% of the way through this course! Two days in a row, nice!