A Picture of the Cosmos

A Picture of the Cosmos is a blog about the universe and everything in it. From black holes to the Big Bang, we cover it all!

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Welcome to A Picture of the Cosmos! This site is dedicated to providing high quality images and information about astronomical objects and phenomena.

Our goal is to provide a resource for amateur astronomers and enthusiasts of all levels of experience, from those just beginning to explore the night sky, to those who have been observing for many years.

We hope that you will find this site useful and informative, and that it will inspire you to explore the cosmos for yourself!

The Solar System

The solar system is the gravitationally bound system of the sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the sun directly, the largest are the eight planets, with the remainder being smaller objects, such as dwarf planets and small solar system bodies. Of the objects that orbit indirectly—the moons—two are larger than the smallest planet, Mercury.

The solar system formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system’s mass is in the sun, with most of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest giant planets—Jupiter and Saturn—are gas giants, being composed mainly of hydrogen and helium; Uranus and Neptune are ice giants, being composed mostly of substances with relatively high melting points compared to hydrogen and helium,—such as water, ammonia and methane—and therefore exist in dense fluid states.*

The Sun

The Sun is the star at the center of the Solar System. It is the Earth’s primary source of light and heat, and drives the Earth’s climate and weather. The Sun is a medium-sized star and is about halfway through its life. It has enough mass to fuse hydrogen atoms together to form helium atoms, releasing energy in the process.

The Inner Planets

The solar system consists of the sun and eight planets orbiting around it. The inner planets are those closest to the sun: Mercury, Venus, Earth and Mars.

Mercury is the smallest and innermost planet. It orbits closest to the sun and has no moons. Mercury is similar in appearance to the moon, with a heavily cratered surface.

Venus is second from the sun and is the hottest planet in the solar system. It is covered in thick clouds of carbon dioxide that trap heat and make it uninhabitable.

Earth is the third planet from the sun and is the only planet known to support life. It has one moon, which orbits around it as it orbits around the sun.

Mars is fourth from the sun and is home to many features that make it seem like a habitable planet, including rivers, lakes and canyons. However, its thin atmosphere means that it currently does not support life.

The Outer Planets

The Outer Planets are those planets found beyond the asteroid belt, including Jupiter, Saturn, Uranus, Neptune, and (for some definitions) Pluto. The gas giants Jupiter and Saturn are by far the largest planets in the Solar System. Uranus and Neptune are much smaller but still comparable in size to Earth. All four outer planets have planetary systems with multiple satellites (Jupiter has at least 67 moons, Saturn 62, Uranus 27 and Neptune 14), and rings.

The outer planets all formed much farther from the Sun than Earth; thus, their material composition is different from that of the inner planets. Jupiter and Saturn are mostly hydrogen and helium gas; Uranus and Neptune are mostly ices (water, methane, ammonia) with small rocky cores. Pluto is unique among the outer planets in that its composition is more like that of the inner terrestrial planets: a rocky core with an icy mantle.

All four outer planets share some striking similarities: low densities (less than 1 gram per cubic centimeter), large sizes relative to Earth (1000 times Earth’s volume for Jupiter, 800 times for Saturn), short periods of rotation (a “day” on Jupiter is only 10 hours long), long periods of revolution around the Sun (12 years for Jupiter, 29 years for Saturn), cold temperatures (-140°C on average for Jupiter,-180°C on average for Saturn), complex planetary systems with multiple moons and ring systems.

Dwarf Planets

Dwarf planets are small, celestial bodies that orbit the sun. Although they are similar to planets in some ways, they are not large enough to be classified as full-fledged planets.

There are five known dwarf planets in our solar system: Ceres, Pluto, Haumea, Makemake, and Eris. Each of these dwarf planets has its own unique characteristics and features.

Ceres is the largest of the dwarf planets, and is also the closest to the sun. It is thought to be made up of a rocky core with an icy mantle. Ceres is also home to one of the largest impact craters in our solar system, called Occator crater.

Pluto is the second largest of the dwarf planets, and is also one of the most famous. That’s because for many years it was considered to be a full-fledged planet before being downgraded in 2006. Pluto is unique because it has an atmosphere made up of nitrogen and methane gas. It also has an intriguing moon called Charon which is half its size.

Haumea is another fascinating dwarf planet. It’s shaped like an elongated oval, and is covered in icy cliffs. Haumea also has two moons: Hi’iaka and Namaka.

Makemake is a small, cold world that orbits far from the sun. Not much is known about Makemake, but it’s thought to have a dark surface covered in methane ice crystals.

Eris is the farthest from the sun of all the known dwarf planets. It’s also thought to be one of the heaviest and most massive objects in our solar system (after Jupiter and Saturn). Eris has one moon called Dysnomia.

Comets and Asteroids

Comets and asteroids are, quite literally, small pieces of the universe. And, like everything else in space, they can tell us a lot about our place in the cosmos.

Comets are small, icy bodies that orbit the sun. They’re often described as “dirty snowballs” because they’re made up of a mix of water ice, dust, and gas. As a comet gets closer to the sun, the ice starts to vaporize and form a tail of gas and dust that points away from the sun.

Asteroids are made mostly of rock and are much smaller than comets. Most asteroids orbit between Mars and Jupiter in an area called the asteroid belt. Some asteroids have orbiting moons (or satellites) just like our planet Earth has one satellite, the moon.

The Kuiper Belt

The Kuiper Belt is a ring of icy bodies orbiting the Sun beyond Neptune. It extends from about 30 to 50 astronomical units (AU) from the Sun. Whereas most planets and asteroids in our Solar System orbit close to a flat plane called the ecliptic, the orbital planes of objects in the Kuiper Belt are highly inclined with respect to the ecliptic. This region is also sometimes called the Edgeworth-Kuiper Belt, after the astronomers who first predicted its existence, Kenneth Edgeworth and Gerard Kuiper.

These objects are leftovers from the formation of our Solar System 4.6 billion years ago, and include dwarf planets such as Pluto, Haumea, and Makemake; comets such as Hale-Bopp; and numerous small icy bodies known as Kuiper Belt Objects (KBOs). Many of these objects have orbits that take them much closer to the Sun than Neptune; some even cross Neptune’s orbit. As a result, they are sometimes referred to as “trans-Neptunian objects” (TNOs).

The Oort Cloud

The Oort Cloud is a large, spherical cloud of comets and other small objects that orbit the Sun at a great distance. It is thought to be the source of long-period comets, such as Comet Hale-Bopp, which has a orbital period of about 2,000 years. The Oort Cloud is believed to extend from about 2 light-years to about 100 light-years from the Sun and may contain as many as a trillion comets.


The universe is enormously vast and incredibly old. Our sun is just one of hundreds of billions of stars in our Milky Way galaxy alone. And there are estimated to be hundreds of billions of galaxies in the observable universe.


Scientists now know that there are billions of galaxies in the observable universe. Each galaxy contains anywhere from a few hundred million to a trillion stars. Galaxies come in many shapes and sizes, from small, dwarf galaxies to huge ellipticals that can span hundreds of thousands of light-years. Some galaxies even have streaks of gas and dust running through them.

The Universe

The universe is all of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy. While the spatial size of the entire universe is still unknown, it is estimated to be at least 93 billion light years in diameter. The earliest scientific models of the universe were developed by ancient Greek and Indian philosophers and were based on geometry, astronomy, and natural philosophy.

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