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Characteristics of the Solar System and the Universe

Characteristics of the Solar System and the Universe

The teacher understands the characteristics of the solar system and the universe.

The universe is defined as everything that exists. It includes all matter found in galaxies and in intergalactic space. The directory of observable objects in the universe is vast. The smallest components are atomic particles followed by atoms (mostly free hydrogen and helium), molecules, dust, space rocks, comets, asteroids, moons, dwarf planets, planets, solar systems, stars, black holes, nebulae, and galaxies. This “ordinary matter” is thought to comprise only about 5% of the total universe. The rest is theorized to consist of dark energy and dark matter.

While universe is defined as everything, there are various multiverse theories that suggest that our universe might be one of many universes that exist, each with different forms of matter and different scientific laws at work.

NASA provides a good overview of the universe, in Universe 101.


Celestial Objects

The beginning teacher understands the properties and characteristics of celestial objects.

Key Concepts:

  • Celestial objects are naturally occurring objects that exist in the observable universe. Each of the hundreds of categories of celestial objects has their own properties and characteristics.

Astronomical or celestial objects are described by property and characteristic in this extensive list on Wikipedia.


The beginning teacher applies knowledge of the earth-moon-sun system and the interactions among them (e.g. seasons, lunar phases, eclipses).

Key Concepts:

  • Earth is a terrestrial (rocky) planet with 6,378 km radius. It orbits the Sun on an elliptical path. Its mean orbital distance is 149.6 million km.
  • The Moon is a terrestrial natural satellite of Earth with a radius of 1,738 km. It orbits Earth at a mean distance of 380,000 km. The Moon orbits Earth approximately 12 times a year.
  • The Sun is a dwarf star with a radius of 696,000 km.
  • Thermonuclear reactions turn hydrogen into helium in the Sun’s interior and produce light and heat for a solar system of 8 planets, moons, dwarf planets, meteoroids, comets, asteroids, etc.
  • The relative positions of the Sun, Earth, and Moon produce optical effects such as lunar phases, eclipses, and seasons.
  • Lunar phases are simply the amount of reflected sunlight we see on the Moon’s surface depending upon the current location of the Moon in relation to the Sun and Earth. When the Moon is between Earth and the Sun, the side of the Moon observable from Earth is in total shadow (new moon). When the Moon is on the opposite side of Earth from the Sun, the near side of the Moon is totally lit by sunlight (full moon). At other positions of the Moon, its near side is partially in sunlight and partially in shadow (crescent, quarter, gibbous).
  • The Moon is gravitational coupled to Earth, causing it to present the same side to Earth at all times. Consequently, the Moon rotates once each orbit.
  • From an observer on the Moon, Earth exhibits phases as the Moon does when seen from Earth.
  • The Moon’s orbit is inclined slightly to Earth’s orbit. This permits seeing the Moon when it is on the opposite side of Earth from the Sun.  The tilt of the orbit causes the Moon to be above or below Earth’s shadow. On occasion, the tilt of the orbit lines up with Earth’s shadow and the reflected light of the Moon is eclipsed. This also can happen when the Moon is between Earth and the Sun so that the Moon blots out the Sun in a solar eclipse (full, partial, or annular depending upon the Moon’s distance when the eclipse occurs).
  • The gravitational attractions of the Moon, Earth, and Sun and centrifugal acceleration of the Earth-Moon system produce ocean tides.
  • The tilt of Earth’s rotational axis creates four seasons during the year.


The following fact sheets from the National Space Science Data Center list detailed properties and characteristics of the Sun, Earth, and the Moon.

Sun, Earth, Moon Fact Sheet: NSSDC

Earth Fact Sheet: NSSDC

Moon Fact Sheet: NSSDC

The National Oceanic and Atmospheric Administration explains tides on its Tides and Currents site.

Phases of the moon are described at the Naval Oceanography Portal.

Windows to the Universe explains why the Earth’s tilt causes seasons.

Properties of the Solar System

The beginning teacher identifies the properties of the components of the solar system.

Key Concepts:

  • The solar system consists of the Sun, planets, dwarf planets, moons, comets, asteroids, meteoroids, dust, atomic particles, electromagnetic radiation, and magnetic fields. Each component of the solar system has its own specific properties.
  • The Sun is a star that produces light and heat energy for the solar system through thermonuclear reactions in its interior.
  • Planets can be rocky (Mercury, Venus, Earth, and Mars) or gaseous (Jupiter, Saturn, Uranus, Neptune).
  • All planets except Mercury and Venus have one or more known natural satellites (moons). The gas planets also have ring systems.
  • Dwarf planets can be rocky or icy or a combination of both.

The planets in the solar system are compared to each other in this data table from the National Space Science Data Center.

Windows to the Universe provides brief descriptions of the planets and other components of the solar system.

Stars and Galaxies

The beginning teacher recognizes characteristics of stars and galaxies and their distribution in the universe.

Key Concepts:

  • Stars are luminous spheres of plasma held together by gravity.
  • Stars produce energy (heat and light) as a byproduct of the thermonuclear fusion of hydrogen into helium.
  • Stars are born in the gravitational collapse of nebulas. When a sufficient mass of hydrogen gas accumulates, a protostar is formed. As matter continues to fall on the protostar, pressure and heat increase until thermonuclear fusion occurs.
  • Stars evolve over a span of tens of millions to several billion years depending upon their sizes. Very massive stars (100 times the Sun’s mass) have a life span in the millions of years. Smaller stars (0.8 to 5 times the Sun’s mass) last much longer.
  • The Hertzsprung-Russell diagram (HR diagram) displays the different known kinds of stars by spectral type, size, color, temperature, luminosity, and absolute magnitude.
  • Spectrograms of the light emitted by stars tells astronomers about star chemical composition, temperature, relative motion (e.g., motion towards or away from Earth or perpendicular to a line connecting Earth and the star), and velocity. For stars moving away from Earth, lines in a spectrogram are shifted to the red end of the spectrum (red shift). For stars moving toward Earth, the lines are shifted toward the blue end (blue shift). The greater the shift, the greater the relative velocity. No spectral line shift is seen in stars moving perpendicular to the line connecting Earth and the star.
  • Our solar system is a part of the Milky Way galaxy. It is a barred spiral galaxy between 100,000 and 120,000 light years across. It contains between 200 and 400 billion stars. The astronomer Edwin Hubble (1889–1953) confirmed the existence of galaxies beyond the Milky Way and created a classification system. There are at least 170 billion galaxies in the observable universe.
  • Many stars in the Milky Way galaxy are part of small clusters that are either open or globular. Open clusters consist of a few hundred widely spaced stars. Globular clusters consist of tens or hundreds of thousands of old stars gravitationally bound.

The HR diagram is presented at the following site.

The Washburn Observatory provides a reference on stars and tables of properties of the 26 brightest stars and the 26 nearest stars.

NASA’s Imagine the Universe site provides information about star properties, the HR diagram, and stellar evolution.

Tour the electromagnetic spectrum (EM) at this NASA site. While the site is aimed at kids, it provides quick and clear information on the different parts of the EM spectrum.

The Hubble Site provides many images of galaxies taken by the Hubble Space Telescope. Press releases explain what the images show.

NASA’s Imagine the Universe explains the characteristics of galaxies and the Hubble classification system.

Origin of the Universe

The beginning teacher demonstrates an understanding of scientific theories of the origin of the universe.

Key Concepts:

  • The big bang theory is the prevailing cosmological model of the initial formation of the universe. Plotting the motion of the galaxies backward indicates that all matter in today’s universe began in a single location called the singularity.
  • According to the big bang theory, the universe began as a hot and dense state that expanded rapidly. The current estimate of when this happened is about 13.7 billion years ago. During the expansion, matter began to cool and energy converted into subatomic particles and eventually atoms. Atoms collected together to form stars and large collections of stars formed galaxies. Today, all galaxies are continuing to move outward, causing the universe to expand.
  • Expansion of the Universe is accelerating. This expansion is attributed to dark energy, which comprises roughly 70% of the Universe, but is not yet understood.

NASA’s Wilkinson Microwave Anisotrophy Probe (WMAP) has mapped the cosmic microwave background radiation for the universe. It confirmed the age of the universe to be 13.73 billion years and produced a map of the residual temperature from the big bang. This site provides information and graphics depicting background radiation and the formation of the universe.

NASA’s Astrophysics site explains dark energy and dark matter.

HISD Project REACH U.S. Department of Education