Gravitational, electromagnetic, strong and weak nuclear forces. Gravitational force is an attraction between any two pieces of matter in the universe. Electromagnetic force is present in pieces of matter, which are able to carry electrical charge. Strong force is holding the nuclei of atoms together. Weak force is responsible for radioactive decay.
Molecules are built from the atoms and atoms consist of protons, neutrons and electrons. Protons and neutrons are built of smaller particles called quarks.
Electromagnetic spectrum is the range of all the light in the universe. Depending on the wavelength and frequency there are radio, micro, infrared, visible, ultraviolet, x-ray and gamma waves with radio wave having the biggest wavelength and the lowest frequency and gamma ray having the shortest wavelength and the greatest frequency.
A star needs to reach the critical mass in order for its gravitational forces to compress the matter enough for the nuclear fusion to start.
Dark matter does not interact with the electromagnetic field, which means that it does not emit or absorb light and, therefore, is invisible, hence the name. The existence of the dark matter has been theorized based on the gravitational effect it seems to have on the visible matter.
Dark energy is associated with the vacuum in space. It is said to be present everywhere in the universe and to accelerate the expansion of the latter. The hypothesis of dark energy was developed in order to explain the universe expansion.
14 billion years old.
Stars form in cold gas clouds. The gravitational forces contract the gas up to the point when it becomes dense enough to start a nuclear fusion between atoms inside it. The internal gas pressure balances the gravitational forces, which pull the particles together and this is how a star remains stable.
Solar system has emerged from a gas nebula, where were particles of rock and metal formed by previous generation stars. After a cataclysmic event (possibly a supernova explosion), the nebula began to compress, eventually flattening and becoming more dense. During this process particles collided and stayed together due to the electrostatic force, once they reached a certain mass, their gravitational force has become strong enough to attract smaller particles and that is how planets started to form. The Sun has formed approximately in the center of the nebula from highly condensed hydrogen.
The main sequence star is a star that is powered by hydrogen fusion.
While at the beginning of its main sequence the star is only starting to burn its hydrogen, at the end of the sequence it does not have any to burn and the outcome depends on the size of the star. Smaller ones collapse into white dwarfs. Stars the size of the Sun first collapse and then expand a few times larger than their original size, forming red giants. Bigger stars collapse and become denser and can remain a white dwarf or eventually explode in a supernova blast.
A galaxy is a system of stars with the gas and dust, which remain together due to the forces of gravitational attraction.
Elliptical, spiral and irregular.
Spiral galaxy (sometimes elliptical).
Elliptical galaxy.
All other galaxies, which cannot be classified as spiral or elliptical.
Millions or billions.
The estimated number of galaxies in the visible universe is one hundred billion galaxies. The researchers have counted the galaxies in a defined region and then multiplied the number up to present a rough estimation.
Edwin Hubble is an American astronomer. He is famous for discovering that the universe is expanding, which is now known as Hubble Law, and that there are galaxies beyond the Milky Way.
The Doppler Effect is the change in frequency of a wave for an observer, which moves relatively to the wave’s source.
Red shift is a phenomenon, which occurs when an object is moving away from the observer and the object’s light waves get stretched into lower frequencies or longer wavelengths.
It can help determine whether a star has planets and also proves the universe expansion theory.
Red shift; cosmic microwave background radiation; mixture of elements that come from different generations of stars.
Their outer boundaries begin collapsing up to the point when the star begins synthesizing carbon, then, under the internal pressure, the star expands a few times its original size and becomes a red giant.
A star condenses and becomes a hot white dwarf.
Most likely, such star is going to condense to a size of a white dwarf and then die in a supernova explosion.
The universe is said to originate from an extremely dense point, which rapidly expanded, creating the known universe. The universe began to expand further and cool down, and chemical elements were created. Then recombination happened, during which electrons combined with nuclei to form neutral atoms. After that first stars emerged from nebulas of gas. 4.6 billion years ago our Solar system was formed.
A method called parallax is used to calculate the distance to stars. Knowing the diameter of Earth’s orbit and the position of the Sun, astronomers can measure the shift of a distant star in relation to the Sun once and then in a six months and then, using the shift, calculate the distance to the star.
