Space Physics

Even if you haven’t thought about it much, space has played an important part in your life and will continue to play an important role far into the future. The vast expanses of the cosmos are the last great frontier for humanity, so we need to talk about what is out there, and how everything out there interacts with everything else. This article is here to give you an overview of each topic that you need to know about within space physics, as well as a very quick rundown of what you’ll learn in each. Make sure to go deep into the articles

What is Space Physics?

Space physics is the branch of physics that tries to answer some of the oldest questions humans have ever had, such as what is our place in the universe? or where did we come from? These questions have been asked for thousands of years and are likely to continue being asked and answered for thousands more.

Space Physics Topics

Within GCSE physics, space physics has a more clearly defined goal. You will have to learn about 4 topics within space physics: Our Solar System, The Life Cycle of a Star, Orbital motions and Redshift. Each of these topics has an associated explanation that goes into a lot more depth than we are going to cover in this one, so make sure you read them!

Space Physics vs Astrophysics

At GCSE level, space physics and astrophysics can be used completely interchangeably. You do not need to worry about any differences between the two. For now, you only need to know and use the term space physics and be aware that astrophysics is a field of research that means essentially the same thing. But just because you don't have to worry, doesn't mean that you can't go beyond the scope of your school curriculum and learn about how space physics and astrophysics are different now!

An Overview of Each Topic

Let’s now take this opportunity to look at each topic within space physics and figure out what each one involves. As you learn each of these topics, you will also be able to start drawing links between them which should also strengthen your overall understanding of space physics.

Our Solar System

• The topic “Our Solar System” explores the objects in the Solar System, and how they were formed. There are 9 major objects in the solar system, including the Sun. In order of distance from the sun, these are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Each of these planets orbits the sun at a different speed and a different orbital radius.
• Some of the planets in our solar system also have objects orbiting them, called moons. Moons are usually substantially smaller than the planets they orbit and are examples of natural satellites. On top of these natural satellites, there are also hundreds of man-made satellites travelling through the solar system each performing different tasks, being used as communications relays or for scientific studies.
• You will also learn about the fusion reaction that keeps a star in a delicate equilibrium between collapsing in on itself and expanding outwards into nothing. This leads quite nicely to learning about the life cycle of a star as well.

The Life Cycle of a Star

Stars are some of the largest individual objects in the universe, and compared to a human lifespan they seem to live forever! Stars do still go through a life cycle, however, just like humans do.

• All stars go through a life cycle from the birth of the star to their inevitable death. The size of a given star determines a few things about its life cycle. The size of a star determines how long a star will live, as well as the stages it goes through leading up to its death.
• At GCSE level, you need to be able to describe the life cycle of two different sizes of stars: stars that are about the same size as the sun and stars that are much larger than the sun. The diagram below outlines the life cycles of these two varying sizes of stars. Notice how no matter the size of the star, they all go through the same first three stages!
  A diagram showing the life cycles of different sizes of stars, Kourosh Simpkins - StudySmarter Originals
• You will also need to learn about how a star generates heat and light. In short, they utilise a process called nuclear fusion. Nuclear fusion is where two atomic nuclei are fused into one nucleus. In main-sequence stars, the fuels used for nuclear fusion are hydrogen atoms. However, as stars reach the end of their life cycles they fuse heavier elements, all the way up to Iron. Any elements heavier than iron were formed in supernovae which spread all of the elements created throughout the universe.

• Several of the elements in the periodic table are formed in the hearts of dying stars. This process is called supernova nucleosynthesis. Another type of nucleosynthesis is stellar nucleosynthesis, which covers all nuclei that are formed in a star at any stage of its life. In fact, most elements are formed because of a reaction or interaction involving stars. Check out the version of the periodic table below for the elements and where they can be formed.

  A version of the periodic table, indicating the main origin of elements found on Earth, By Cmglee - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31761437

Orbital Motion, Natural and Artificial Satellites

Companies and countries spend a lot of time, manpower, and money sending satellites into space to perform a variety of tasks. Some satellites are used for global navigation, like the GPS or GLONASS constellations. Other satellites may be used for satellite internet connections, like SpaceX's Starlink constellation. Importantly, every single one of these satellites has had its orbital speed calculated at one point or another in its life. We want to know the orbital speed of a satellite so that we can ensure that it remains in orbit.

If the orbital speed of any satellite ever dropped below the minimum speed to orbit the Earth, engineers would immediately want to know why that happened, as well as find a way to fix it. Because it is very likely that you either directly or indirectly use at least one of these satellites a day, calculating orbital speed is a daily part of life that you may never have considered, and essential to the modern world.

• The force that causes objects to maintain circular orbits is gravity. Every object in the universe has a gravitational pull, however, you probably don't feel the gravitational pull of people or other relatively small objects, because it only really has a noticeable pull when the object has a very large mass, such as a planet.

• Not only does every object in space exert a gravitational pull, but they also have an orbital motion that defines how the object moves through space. For a circular orbit, the speed of the orbit is constant, but the velocity is constantly changing. Remember, velocity is the speed of an object in a given direction. In the diagram below, the speed of the planet doesn't change but notice that the velocity changes between location 1 and location 2 due to the change in the direction of the object's motion as it moves from location 1 to location 2.

  A diagram displaying the velocity and force vectors of an object orbiting in circular motion around a more massive body. StudySmarter Originals

Red-Shift

There are a few theories that explore how our universe came into existence. These theories are based on observations that astronomers have made and on looking at concepts such as red-shift and dark energy. As part of the red-shift topic, we'll also explore and explain the big bang theory.

• Red-shift is the phenomenon of light we observe from distant galaxies being 'redder' when it reaches Earth than when it was originally emitted by a galaxy. The light's wavelength is shifted towards the red end of the visible spectrum. One source of red-shift is the expansion of the universe. The expansion of space causes galaxies that are further away from us to recede from us faster. The light waves emitted by further and relatively faster-moving galaxies are red-shifted more than closer slower galaxies. The more red-shifted the light from a galaxy is, the faster the galaxy is moving away from us.
• The fact that we can observe red-shift is evidence supporting the big bang theory. The big bang theory suggests that the universe began as a very small region that was extremely hot and densely packed. This theory is further backed up by the fact that the universe seems to be expanding, and we have observed this expansion thanks to red-shift.
• There is still more about the universe that we do not know. Two such examples are dark energy and dark matter.

• Scientists are not completely sure why the rate of expansion of our universe is increasing, however, some have theorised that it is due to a phenomenon we have not yet fully discovered called dark energy.

• Dark matter was theorised due to observations of galaxies rotating too quickly for the mass that they contain. We only know of its existence because it has a gravitational effect on nearby objects, but we have never directly observed it.