What is a Nebula?
A nebula is a general term given to what are considered to be interstellar clouds of dust and gas. These clouds can take on many shapes and tend to travel through space. Nebulas are often made up of ionized gases with stars born within them. They also contain dark matter, which does not emit electromagnetic radiation and is only detectable by its gravitational effects. Nebulas vary in size, with the smallest being those created by the collision of two small molecular clouds. At the same time, the largest will have a diameter spanning several hundred light years.
How Does a Nebula Form?
The process by which nebulae form is often referred to as "gravitational collapse." Gravitational collapse is when a cloud of gas begins to contract in on itself due to its gravity. At this point, the cloud becomes dense and hot, which causes it to release radiation. When the radiation from the cloud is released, it causes pressure within the cloud, which causes some of it to expand further into space. When this occurs, the gas within that region begins to ionize and becomes known as a nebula. At this phase, the gas is ionized because it does not have enough time to cool off before the next expansion occurs. The expansion of these nebulae also causes material to be ejected from them, often seen as a dense cloud made up of dust and gas that are moving rapidly. Through this material cloud, new stars are born within nebulae.
Where to Find Nebulae
Nebulae are often found in what is known as the interstellar medium, which is made up of primarily ionized material that is located between stars. When stars are born from nebulae, the ionized gases that make up the nebulae become part of the new star. The closest nebula to Earth is the Helix nebula, located in the Aquarius constellation. The Helix nebula is approximately 700 light-years from Earth. This means it would take a spaceship traveling at the speed of light 700 years to reach the Helix Nebula.
- Some nebulae can be seen with the naked eye, while others are only visible through a telescope. The Helix Nebula is one of the nebulae that can be seen with the human eye. It is classified as an emission nebula, which means it glows because of the radiation it emits.
- Some nebulae can be seen from Earth during the day and night, but they are most visible during the night since they are illuminated by nearby stars, which cause their gases to glow. The size of these nebulae also changes with their location. Nebulae found near us may get covered up by our atmosphere, but those far away will be much more visible to us.
What are the Types of Nebulae?
Today, scientists and astronomers classify nebulae into five different types.
Type #1: The Eagle Nebula
The Eagle Nebula is one of the most iconic deep-space objects in the night sky. It is located in the constellation Serpens, which can be seen with binoculars and telescopes. Its name comes from its resemblance to an eagle observed through a telescope. The Eagle Nebula is also known as Messier 16 (M16) and NGC 6611, which are two names that derive from its appearance when observed through a telescope. It contains the pillars of creation and was discovered by Jean-Philippe de Cheseaux in 1745. In this region, stars are formed from these pillars. The Eagle Nebula is approximately 7,000 light-years from Earth and has been around for 5.504 million years.
Type #2: The Helix Nebula
As mentioned earlier, it’s located in the constellation of Aquarius and can be seen with binoculars. The Helix Nebula is also known as NGC 7293, which is its identifier when referenced by scientists. It is a planetary nebula with a diameter of approximately 0.3 light years. The Helix Nebula is one of the brightest and easiest-to-see nebulae from the Earth's surface without using a telescope. Karl Ludwig Harding discovered it in the 1800s. The Helix is one of the closest nebulae to Earth, which makes it the easiest to view. The distance from Earth to the Helix Nebula is approximately 700 light-years away.
Type #3: Omega Nebula
Located in the constellation of Sagittarius, the Omega Nebula is the largest and brightest emission nebula in our night sky. This nebula can be seen with binoculars and telescopes, but it is most commonly viewed with a telescope. Philippe Loys de Chéseaux discovered it in 1745. Omega Nebula is also known as Messier 17 (M17), which refers to how it appears through a telescope; it is also known as Checkmark Nebula, Horseshoe Nebula, Lobster Nebula, and Swan Nebula.M17 is more than 5,000 light-years from Earth.
Type #4: Trifid Nebula
Trifid Nebula is located northwest of Sagittarius; it is a forming star in the region of the Milky Way's Scutum-Centaurus Arm. It is 5,400 light-years from the constellation of Sagittarius. Charles Messier discovered it in 1764. The Trifid Nebula is a combination of emission wavelengths surrounding an emission nebula; in other words, it is composed of radiation and dark clouds.
Type #5: Lagoon Nebula
A forming star visible from the mid-northern latitudes, the Lagoon Nebula is located in the constellation of Sagittarius. Lagoon Nebula can be seen without a telescope, which is why a number like some other nebulae does not designate it. This nebula can be found in the constellations Sagittarius and Orion. Giovanni Hodierna discovered the Lagoon Nebula in the 1640s. It’s approximately 4,077 light-years from Earth.
How Do We Know What Nebulae Look Like?
Astronomers use telescope observations and multi-wavelength light observations to determine how nebulae look. Space telescopes such as the Hubble Space Telescope and NASA's Spitzer Space Telescope are used to receive light wavelengths and perform spectroscopy. These telescopes enable astronomers to determine how nebulae are formed and where they come from. By observing the motion of stars born within nebulae, they can decide whether they are forming or existing inside a nebula. By watching the movement of stars created within the clouds of an emission nebula, one can see which way they are moving because those clouds move at a different rate than the gas clouds outside them. Observations made with space-based telescopes such as the Hubble Space Telescope can assist astronomers in determining how far away previously unstudied nebulae are located, as well as what parts of them glow for longer periods of time.
The nebulae are the most well-known and recognized objects in the universe for their surreal beauty, grandeur, and mysteriousness. They significantly influence our world because they shape some of the star formations within their orbits.