How to Write a Compare & Contrast Essay in Astronomy

Writing guide
Posted on September 12, 2019

Already in ancient times, astronomical observations played a very significant role in the life of humankind. With the help of celestial bodies, our ancestors found the right way in the ocean, measured time, made calendars, determined the most favorable terms for agricultural work. Astronomical observations have helped people measure the Earth, draw up geographical maps.

But astronomy has acquired particular importance in our time, in the era of the so-called scientific and technological revolution. Without it, many achievements of science and technology, including the successes of modern humankind in space exploration, would have been impossible.

The role of basic research has especially grown. It is such studies that lead to the most significant changes in technology, open up new areas of human activity. Writing a Compare & Contrast Essay is one of the steps to full-fledged basic research. That is why students often get this task, and we will tell in detail how to deal with it.

The Essence of Compare & Contrast Essays

As the name implies, the essence of this work is to find and compare common and different signs of two objects. To do this, we need to find and highlight several features of the object, which hypothetically can be both common and different, and conduct research on each of them.

For example, see the standard structure of this type of essay here. Further, we will analyze this approach on practical topics and examples, and you will gradually understand how to cope with this task.

What to Compare, What to Contrast

Research in astronomy is divided into such important areas as the study of the solar system, interstellar matter, and the galaxy. It is quite possible to find two suitable objects for comparison and contrasting within these areas. See for yourself.

Solar System Exploration

Studying the mechanics of the motion of celestial bodies makes it possible to build calculations that allow various earthly vehicles launched into space to achieve their intended purpose. For example, you can also compare the trajectories and flight results of two such devices.

When exploring the Sun, experts answer questions related to various physical phenomena that occur on the star closest to us. In particular, such phenomena as thermonuclear reactions, other processes associated with high temperature, as well as radiation emanating from our luminary, and its effect on the atmosphere and biosphere of the Earth are studied. For example, you can compare and contrast the indicators of solar activity in different time periods.

Meteorites are also important for exploring the past of our solar system. Their age is estimated at 4.5 billion years. It will be interesting and original to compare meteorites, their sizes, causes, and consequences.

It is also important to study comets that were formed during the youth of the solar system. Thus, comets carry the primary substance of the early solar system. Everything can be done here by analogy with meteorites.

Comparative Study of the Planets

The terrestrial planets, despite their similarities between themselves, differ from each other in size, internal structure, and composition of the atmosphere. First of all, these differences are determined by the peculiarity of those regions of the protoplanetary cloud in which they were formed, by interaction with the Sun and other planets.
By exploring and comparing the motion of the planets, students can consider the laws of interaction of bodies in action.

Comparing and Contrasting the Internal Structure of Planets

For example, we can talk about comparing the internal structure of planets in the solar system. We know that there are two large groups of planets. These are the inner planets, the terrestrial planets: Mercury, Venus, Earth, and Mars, which have basically a solid surface with a fairly thin shell, which may also be absent, like in Mercury. Inside, these planets are well-differentiated, that is, the substance is divided into the heavier components that make up the core – it is mainly iron and the lighter – silicates that float on the surface.

The second group of planets is giant planets, gas balls. Typical representatives are Jupiter and Saturn, followed by Uranus and Neptune, and these are planets, which are mainly composed of solar gas mixed with rocks and ice. That is, studying these planets, we see how the formation of celestial bodies took place in different areas of the solar system.

Further, if we talk about the geology of celestial bodies, we also find a lot of similar things on different planets, as well as differences.

Comparing and Contrasting Surfaces

If we compare the surfaces of Mars and the Earth, we can talk, for example, about volcanoes. For example, students can compare giant volcanoes in the Tarsis region, such as Olympus Mons or Arsia Mons, which are called shield volcanoes, and we have analogs of these volcanoes on Earth – for example, the volcanoes of the Hawaiian ridge.

Comparing and Contrasting Atmospheres

If we talk about the atmosphere of planets, then the mechanisms that are responsible, for example, for the formation of the temperature structure in the atmosphere, are very similar to different planets.

Take the Earth or, say, Jupiter – everywhere we see the upper atmospheres, which are called thermospheres, we see that the mechanisms of radiation heat transfer and energy transfer due to molecular diffusion work there, we see how the nature of the temperature changes depending on the composition of these planets.

For example, on Earth, the thermosphere reaches exceptionally high temperatures – on the order of a thousand degrees Kelvin, while on Mars and Venus these areas are even called cryospheres, because there the temperatures are not higher than 200 degrees Kelvin.

This is due to the fact that the main component in the composition of Venus and Mars is carbon dioxide – a very strong cooling agent, cooling gas, which has very strong emission and absorption bands in the infrared range, and through them, the thermosphere releases its energy into space. While in the atmosphere of the Earth this gas is contained in negligible amounts, and the thermosphere is heated to this temperature.

We described these processes briefly, and you can take this information as the main idea and turn it into a comparative study, highlighting common and distinctive features, and backing it up with statistical data and formulas.

Comparing and Contrasting Substance Loss

Next, you can compare the rates of substance loss by planets. At the moment, we have very accurate measurements of flue gas flows from Venus, Earth, and Mars. Such measurements are made on spacecraft, and when we compare them, we see that it turns out, the Earth is losing more substance than Venus and Mars. And this caused great surprise for scientists since it was previously believed that the Earth, which is protected by a magnetic field, should lose less substance when interacting with the solar wind. In fact, measurements show that the Earth is losing more substance, more gases are leaving as a result of plasma processes from the upper atmosphere of our planet.

Take this idea as the basis of your essay and compare and contrast the process of substance loss by other planets, as well as the causes and consequences of this process.

Comparing and Contrasting Atmospheric Dynamics

Another example is atmospheric dynamics. Earth and Venus are planets of almost the same size, they receive almost the same amount of solar energy. The only thing that they have different is the speed of rotation around their axis. And we see dramatic differences in the dynamics of atmospheres.

On Earth, we are all accustomed to changing cyclones and anticyclones, that is, to changing the weather – this is the so-called wave mode of circulation. While Venus does not produce these cyclones and anticyclones at all, and the entire atmosphere of the planet rotates with great speed, almost as a whole around a solid body and with speeds reaching about 150 meters per second at the upper boundary of the clouds. This difference is precisely due to the fact that Venus rotates very slowly around its own axis, plus, of course, there are some differences between the Earth and Venus in how and at what altitudes solar energy is absorbed by the planet.

Find these differences and match them.

An interesting comparison can be made if we compare the temperatures on the surface of the planets – the so-called greenhouse effect. This is the difference in surface temperature between a really existing planet with the atmosphere and a hypothetical planet from where the atmosphere is removed.
For example, for Venus, this difference is about 500 degrees. On Earth, the greenhouse effect also exists, but it is much smaller – about 30-40 degrees. On Mars, which has an atmosphere a hundred times weaker than Earth, this greenhouse effect is only 5 degrees.

Comparing the greenhouse effect, we see how different gases work at different temperatures and atmospheric densities.

Comparing and Contrasting Stars

Researchers distinguish stars according to such characteristics as the distance from the Earth, mass, luminosity (radiation power), temperature, chemical composition, age and speed of movement.

And this is a very wide scope for research. Choose any two stars and compare their indicators until you reach the desired volume of your essay.

Galaxies Research

A study of neighboring galaxies has led to the conclusion that galaxies are diverse in their shapes, sizes, and masses. Moreover, the stars of which they are composed and which it is possible to observe are similar to those that surround us. It is also revealed that galaxies are moving away from us. The further they are located, the faster this process occurs.

Comparing galaxies is an even more interesting process than comparing stars. And here you can write a whole dissertation and not just one essay. Therefore, we recommend that you select only two-three signs of two galaxies and compare them, otherwise you will analyze all the possible similarities and differences until the end of time.

Algorithm and Example for Comparing Two Planets

According to their physical characteristics, planets are divided into two groups – planets of the earth group and planets – giants. We will give an overview of the main features of both groups of planets, on the basis of which you will be able to give a description of each planet.

General characteristics of the terrestrial planets

Planets belonging to the earth group are small in size and mass, the average density of these planets is several times higher than the density of water; they rotate slowly around their axes; they have few satellites.

Earth is the largest in the earth type and has a huge amount of liquid water. It is needed for a life that develops in all forms. There is a rocky surface, sheltered by canyons and hills, as well as heavy metalcore. Water vapor is present in the atmosphere, helping to mitigate the daily temperature regime. There is a change in regular seasons. Most heat goes to areas near the equatorial line. But now, indicators are growing due to human activities.

Mars has the highest mountain in the solar system. Most of the surface is represented by ancient sediments and crater formations. But you can also find younger sites. There are polar caps that reduce their size in the summer and spring. It is inferior in density to the Earth, and the core is solid. Researchers have not yet obtained evidence of life, but there are all hints that this is possible. The planet has water ice, organic matter, and methane.


This is a very correct statement that astronomy is a science of infinity. The possibilities for scientific research within its framework are really endless, as are the possibilities for searching for general laws, differences, causes and effects.

The main feature of astronomy is that it studies many objects, both individually and in total, which gives the student the opportunity to choose the most interesting objects for research and compare their characteristics. Feel free to use tips, ideas and examples we have provided, and do not forget that you are not limited to them only. In astronomy, even the sky is not a limit. It is just the beginning of all innovative discoveries come.

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