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Key Facts & Information

  • The Universe is practically everything. From space, time, and their contents, which include planets, stars, galaxies, to all other forms of matter, and energy. Everything is part of the Universe, and the Universe is part of everything. Many of the earliest cosmological models of the Universe were developed by ancient Greek and Indian philosophers.

Early Times

  • Ancient Greek and Indian philosophers’ models were geocentric – placing the Earth at the center. Over many centuries, much more precise astronomical observations were conducted and led to our current understanding of the Universe.
  • Nicolaus Copernicus developed the heliocentric model – being the first to put the Sun in the center.
  • Upon Copernicus’s work, Isaac Newton started to develop the law of universal gravitation – every particle attracts other particles with a force based upon their mass/weight.
  • Johannes Kepler also built upon Copernicus’s work and established the laws of planetary motion. Observations conducted by Tycho Brahe also helped this.
  • Galileo pioneered the use of telescopes, discovered the Galilean moons, and the conglomeration of stars in the Milky Way. He thus undermined the idea that everything revolves around the Earth.
  • Many studies were conducted, ideas caught up, morphed, and finally, it was established that Earth was a planet among many others, while the Sun was a star among billions of other stars.
  • After this, there was a period of time when the Universe was associated with the Galaxy – meaning – people believed that the galaxy was actually the Universe, with clouds of nebulas around it.
  • With more modern telescopes being used, an astronomer by the name of Edwin Hubble studied the Andromeda nebula. He concluded in 1923 that the nebula was, in fact, another galaxy.
  • Hubble discovered many galaxies and devised the Hubble sequence – a system of classification for galaxies, based upon their morphology.
  • Another achievement of Hubble was what is now being called the Hubble constant – Edwin Hubble’s observations concluded that objects that were farther away from Earth were moving away faster – meaning – the Universe itself is expanding.

Big Bang Theory

  • The Big Bang theory states that the early Universe was a hot place that expanded, and began to cool down. This means that the Universe should be filled with radiation, which is actually the relic/leftovers of the Big Bang event.
  • It is like a cosmic echo and the most amazing fact is that old-fashioned television sets would catch a glimpse of this – around 1% of the black and white fuzz and clacking white noise when these old TVs weren’t turned on a station.
  • The most accepted explanation of the Universe’s mysterious genesis is the Big Bang Theory.
  • Contrary to popular belief, the Big Bang didn’t start as an explosion, but rather as a hot and infinitely dense point similar to a supercharged black hole – being just a few millimeters wide – that suddenly started to expand. Matter, energy, space, and time were thus created.

Major Stages Of The Universe’s Evolution

  • Radiation Era. The first era named after the dominance of radiation right after the Big Bang. It is made up of smaller stages called epochs. These stages occurred in the Universe’s first tens of thousands of years. In chronological order:
    • Planck Epoch – Matter as we know it, only existed in the form of energy. Only energy and the ancestor of the four forces of nature, the super-force, were present. At the end of this stage, a key event occurred. This event split away gravity from the super-force and made way for the next epoch.
    • The Grand Unification Epoch – It is named after the remaining three unified forces of nature (Strong Nuclear, Weak Nuclear and Electromagnetic). This epoch ended when the strong force, or strong nuclear, broke away, leading to the next epoch.
    • The Inflationary Epoch – In this epoch, the Universe rapidly expanded. In an instant, it grew from the size of an atom to that of a football. It was a hot period as the Universe churned with electrons, quarks, and other particles that led to the next epoch.
    • The Electroweak Epoch – A different event took place in this epoch. Not one, but both remaining forces of nature – electromagnetic and weak nuclear – split off as well.
    • The Quark Epoch – Around this epoch, all of the Universe’s ingredients were present. Though, it was still a period of high temperatures and density, preventing the formation of subatomic particles.
    • The Hadron Epoch – During this epoch, temperatures started to drop. The Universe cooled down enough, thus, quarks were able to bind together and form protons and neutrons.
    • The Lepton and Nuclear Epochs – The last two stages of the radiation era. During these epochs, the protons and neutrons underwent a significant change – they fused together and created nuclei. This led to the creation of the first chemical element in the Universe, helium.
  • Matter Era. The ability to form elements ended the radiation era and gave way to the matter era. It is named after the presence and predominance of matter in the Universe. This era features three epochs that span for billions of years.
    • Atomic Epoch – This stage is characterized by the Universe’s cooling temperature. Because of this, electrons were able, for the first time, to attach themselves to nuclei. This process is called recombination, and it led to the creation of the Universe’s second element, hydrogen.
    • Galactic Epoch – Hydrogen and helium atoms painted the Universe with atomic clouds. In these atomic clouds, small pockets of gas may have had enough gravity to cause atoms to collect. Clusters of atoms formed during this epoch, and became the seedlings of galaxies.
    • Stellar Epoch – Inside these galaxies, stars began to form. This epoch is the last, yet ongoing epoch of the matter era. Since stars began to form, they caused a ripple effect and helped in the shaping of the Universe.
  • The heat within the stars ultimately caused the conversation of helium and hydrogen into almost all the remaining elements in the Universe. These elements became the building blocks for planets, moons, and ultimately life. The age of the Universe has been predicted to be around 13.8 billion years old. Since the Universe is expanding, the initial energy and matter became much less dense over time.
  • The dominant fundamental force – forces of nature – out of the four, is gravity. Its effects are cumulative. Interestingly, the Universe appears to have much more matter than antimatter. This imbalance, however, is partially responsible for the existence of all matter existing today in the first place.
  • Another physical property of the Universe is that it doesn’t have net momentum or angular momentum which follows accepted physical laws, if the Universe is finite. There is no place where the Universe began, it happened everywhere at once.

Size, Structure – Regions

  • The Universe’s exact size is difficult to determine. It does not have a center nor an edge – this is evidenced by the fact that when observed at the largest scale, galaxies seem to be distributed uniformly and at the same time they appear in all directions.
  • When it comes to smaller scales, these galaxies are distributed in clusters and superclusters – which are large groups of smaller galaxy conglomerations.  They form immense filaments – the largest known structures in the Universe.

Age & Expansion

  • It is believed that our Universe has the right mass-energy density, equivalent to around 5 protons per cubic meter, which allowed it to expand for the last 13.8 billion years.
  • Because of this expansion, we can observe the light from a 30- billion light-years away galaxy, even though that light has traveled for only 13 billion years – the very space between them has expanded. The light from distant objects in the Universe is red-shifted. This tells us that all the objects are moving away from us.
  • In addition to this expansion, there is also an accelerating factor. Studies determined that space expands at 72 km / 44.7 mi per second per megaparsec – around 3.3 million light-years. 
  • This means that for every 3.3 million light-years further away from the Earth you are, the matter where you are is moving away from Earth 72 km / 44.7 a second faster.
  • Many scientists attribute the current acceleration rate of expansion to dark energy. Dark energy is a mysterious yet hypothetical form of energy that has anti-gravitational properties.

Space-Time & Shape

  • Space-time is an area in which all physical events take place. These events are the basic elements of space-time. Many scientists believe that unlike Earth, the Universe may be flat. However, there are 2 other possibilities.
  • The density parameter – Omega, is defined as the average matter density of the Universe divided by a critical value of that density. This gives birth to three possible geometries, depending on whether Omega is equal to, less, or greater than one. These are called, respectively, the flat, open, and closed Universes. Observations continue in the effort of establishing the shape of the Universe.


  • The Universe is estimated to be made up of 4.9% ordinary (baryonic) matter, 26.8% dark matter, and 68.3% dark energy. Considering only the largest structures, the Universe is made up of filaments, voids, superclusters, and galaxy groups, and clusters.
  • Dark matter and dark energy are invisible theoretical matter. The only proof of their existence lies in certain phenomena, which mostly tell us that huge chunks of mass are missing, thus, in a way, justifying their probable existence.
  • Quasars played an important role in the investigation of helium. They are the Universe’s lighthouses, and their light changes as they pass through intergalactic matter, revealing the composition of gasses.
  • Helium and hydrogen are the most abundant elements in the Universe and are commonly found in stars and gas giant planets. Stars are mostly formed from hydrogen and helium gas. The heavier elements of the Universe are commonly found in planets such as ours.
  • When it comes to particles, neutrinos have no charge and it is generally believed that they have little mass. They are created in energetic collisions between nuclear particles. The Universe is filled with them though they rarely collide with anything. Everything, with the exception of dark matter and energy, is ordinary baryonic matter.