Many think that this is because the Earth acts as a shield for the near side of the Moon so the far side is the one that has suffered the heaviest bombardment. However, this is most probably not the case. The Earth is in fact a very small, practically a negligible shield of the near side of the Moon. 

Let’s see an explanation offered by David Morrison, Senior Scientist and Brad Bailey, Staff Scientist:

“The real reason there are more impact craters on the far side of the Moon is that the near side has a much thinner crust which has allowed volcanoes to erupt and fill in ancient large basins (or large impact craters). These large lava flows have covered craters that were formed early in the Moon’s history through the late heavy bombardment, which is when the largest percentage of impacts were occurring in the inner solar system. It is likely that each side of the Moon has received equal numbers of impacts, but the resurfacing by lava results in fewer craters visible on the near side than the far side, even though the both sides have received the same number of impacts. Further, the oldest areas in both near and far side are saturated, meaning that they have reached equilibrium (each new crater, on average, destroys one old one). In this case, the density of craters is no longer an accurate measure of the number of hits the surface has received.

If you have young students, you can stir up their imagination by giving them a picture of the full Moon and ask them to draw anything that the areas of the Moon reminds them of. This is a little intuitive drawing activity, similar to the game we often do with cloud shapes when trying to imagine what they could depict. 
Students can also engage in a little personal geography activity. Ask your students to create their own map of the Moon, by naming the Maria, highlands and craters using names of their choosing. The names the students could think of using could be the names of their family members, their favorite heroes, their favorite football team, words that remind them of happy memories, they can be anything the students come up with!

Since then, missions have been limited to lower orbit missions (less than 500km from the Surface of the Earth).  However, lunar missions did not come to an end in the 1970’s. The Moon is once again among the destinations of future missions. Have a look at the video below to learn more:

You can find out more about heliophysics here. 

One of the most important phenomena that take place on the Sun is the gases streams that the Sun ejects which can pass past the Earth at incredible speed (about 500km/sec). We refer to these streams as solar wind. Solar wind can have an effect on the Earth’s magnetic field. It can affect or damage satellites, threaten the life of astronauts and cause problems to power stations and power lines on Earth.  Space weather studies how solar wind and the phenomena that take place on the Sun affect the Earth and other planets. As technology progresses, space weather starts to play an increasingly important role. Scientists study in great detail phenomena that are related to space weather like CMEs, solar flares and sunspots in order to understand them and protect human infrastructures.  Here is a video on space weather.

Let’s have a look at what they did.

Our Sun may be unique in the sense that it is the star that supports life on Earth, but other than that, it is anything but unique. Our Sun is a star. A medium-sized star to be exact. There are stars that are 10 times smaller and stars that are 50 times bigger. It is just like the stars we see on the night sky. The only reason we see it so big and during the day is because it is very close to our Earth compared to all other stars. To get an idea how close, our Sun is about 150 million kilometers away from Earth, while the next nearest star (Proxima Centauri) is 4.24 light years (or 9,460,730,472,580 km!) away. To put it in perspective, light from the surface of the Sun reaches Earth in 8.3 minutes, while from the surface of Proxima Centauri to Earth in needs 4.24 years.

The Sun has 1.4 million km diameter, while the Moon is a little less than 3 500 km across. The reason why we have eclipses is their relative position to Earth. To help your students understand that, ask a student to stand still and another to move away far enough so that the first student can cover the second with his/her thumb. Is the second student really the size of a thumb? 

As we have seen in the information presented above, the Sun is not ‘quite’. It is not like a switched-on lightbulb that simply emits light. There are numerous events and phenomena going on constantly. Solar activity follows an 11-year solar activity during which the Suns activity differs.  

Aside from having dedicated classes with your students about the Solar System, you can also use fun facts like those we mentioned above, ad hoc in your class, as inspiration or food for thought and discussion. Talking about the Solar System does not necessarily need to happen all at once; you can keep feeding your students with information through different classes. This approach can help you not only spice up your everyday teaching, it can also facilitate you in helping your students understand that all science disciplines are connected and to their total, they are used to describe the same thing, our world!

Finally have a look at some activities for your students:

When talking about the basics of the Solar System, many teachers choose to focus on the scale. Giving your students a proper understanding of the scales of our Solar System and ensuring that the models presented to them are correct is an important point. To this end when creating such models, here is an idea on how to do it using the correct scales.

As it is too difficult to have the Sun and all the planets in the correct dimensions, perhaps you could consider building two separate models. One showing the Sun with respect to the planets (Image 1), and one that introduces the planets alone (Image 2).

Image 1, Via: Wikimedia commons

Image 2, Via: Wikimedia commons

When talking about the basics of the Solar System, many teachers choose to focus on the scale. Giving your students a proper understanding of the scales of our Solar System and ensuring that the models presented to them are correct is an important point. To this end when creating such models, here is an idea on how to do it using the correct scales.

As it is too difficult to have the Sun and all the planets in the correct dimensions, perhaps you could consider building two separate models. One showing the Sun with respect to the planets (Image 1), and one that introduces the planets alone (Image 2).

Juno set out to understand the origin and evolution of Jupiter. It was launched on August 5, 2011 and it successfully entered the orbit of Jupiter on July 4, 2016. For the first time, we will be able to peer below the dense cover of clouds to answer questions about the gas giant and the origins of our solar system.

Two missions are foreseen within the ExoMars programme: one consisting of the Trace Gas Orbiter plus an Entry, Descent and landing demonstrator Module (EDM), known as Schiaparelli, launched on 14 March 2016, and the other, featuring a rover, with a launch date of 2020. Both missions will be carried out in cooperation with Roscosmos.”

The 2016 Trace Gas Orbiter’s (TGO) mission is to gain a better understanding of methane and other atmospheric gases that are present in small concentrations (less than 1% of the atmosphere) but nevertheless could be evidence for possible biological or geological activity. The instruments onboard the Trace Gas Orbiter will be deployed to detect a wide range of atmospheric trace gases (such as methane, water vapor, nitrogen oxides, acetylene), with an improved accuracy of three orders of magnitude compared to previous measurements.

Source: http://exploration.esa.int/mars/46475-trace-gas-orbiter/

The Exomars rover will be launched on 2020. The primary objective is to land the rover at a site with high potential for finding well-preserved organic material, particularly from the very early history of the planet. The rover will establish the physical and chemical properties of Martian samples, mainly from the subsurface. Underground samples are more likely to include biomarkers, since the tenuous Martian atmosphere offers little protection from radiation and photochemistry at the surface. 
The ExoMars Trace Gas Orbiter, part of the 2016 ExoMars mission, will support communications.

The Sun emits energy that is crucial for life on Earth. The amount of energy received on Earth affects our climate and all subsystems of our planet. Let’s see a little bit about solar radiation itself.

To many people the term ‘electromagnetic radiation’ is identified with some kind of dangerous radiation that is harmful to living organisms. However, this is not exactly the case. Electromagnetic radiation is in fact light. Depending on the wavelength (or frequency) of the radiation, we have different bands - from gamma rays to visual light and radio waves. Visible light is the only type of electromagnetic radiation that is visible to humans. Some animals and insects have the ability to see colors beyond the visual spectrum. Before talking about solar radiation let’s see a few things about electromagnetic radiation in general, to clarify some misconceptions.

Galaxies are the neighbourhoods of stars. They are systems of hundreds of billions of stars but how many stars are there in the Universe? How can we count them? Can we see them all? Counting the stars is not an easy task for sure! First, we need to clarify that we can only speak about the stars that we can observe. This is why we often talk about the “Observable Universe”. That is the part of the Universe we can observe. Why can’t we see the entire Universe? Because light has a finite speed! A first estimation is that the observable Universe is as big as light could travel since the beginning of the Universe, which would be around 13.8 billion years ago. That means that the observable Universe could be around 13.8 billion years in radius. Well… not exactly. There are other factors to take into consideration, like the expansion of the Universe.  A photon that was born during the big bang and has travelled 13.8 billion years to reach us, by the time we detect it, it has travelled much further away from us than where it originally was, making the observable Universe much bigger than 13.8 billion light years. So how big is the observable Universe? Around 45.7 billion light years. 

You can use the “Observing with NASA” robotic telescope network to take an astronomical observation of different celestial objects. It can be used to take an observation of two interacting galaxies. Then use this “Galaxy Crash” simulation and try to tell the story of these galaxies. Based on the simulation students can understand how these two galaxies where before they started to interact, how much time has it been since they started interacting and what will happen to them in future. Here you can find the answer keys for playing with M51 and its companion and the antennae galaxy in a galaxy crash.

More about galaxies

As we mentioned earlier, when stars burn hydrogen in their core, which is the better part of their lives, they are located in the main sequence of the H-R diagram. When hydrogen stock runs out, the star compresses its core in order to increase its temperature and continue producing energy by fusing helium into carbon. This compression is so abrupt that the outer layers of the star get detached, they start expanding and lose energy fast. This causes the star to get a lot bigger and red. This is the phase when a small star becomes a “Red Giant”. More massive stars, manage to get their core temperature high enough to fuse carbon and heavier elements all the way to iron. More massive stars become “Red supergiants” instead. Red giants can be 10 to 150 times bigger than the initial star. A star like our Sun, when it becomes a red giant will become about 2000 times brighter.

Red supergiants, that get to the point of fusing silicon to iron reach a core temperature of about 3 billion degrees. Their outer layers get so swollen, they can reach a diameter of a billion kilometres.

Small mass stars (up to 8 solar masses) after going through the phase of red giants and their outer layers get blown away from the core of the star, what remains is basically their naked core. That naked core is what we call a “White Dwarf” which eventually cools down over billions of years and eventually becomes black. The core of the original star is now super dense (about a million  times the density of the sun), hot (about 100.000 degrees) pile of carbon ash roughly the size of the Earth, with incredible gravity. Imagine that a cough drop of white dwarf material equals the weight of a car on Earth! Normally, a white dwarf has such tremendous gravity, that it would collapse. However, this is not what happens thanks to quantum mechanics. Pauli’s exclusion principle and Heisenberg’s uncertainty principle keeps the mass from becoming any denser and thus the white dwarfs survives. Due to the quantum phenomena, the matter of white dwarfs is called “degenerate” which means it has some very peculiar properties. For example, the more massive the white dwarf, the smaller its size!

Depending on the mass of the star (as usual!) in some cases, when the outer shell of a star gets blown away, it will form something like a gaseous cloud around the white dwarf that remains. That is what we call a “Planetary Nebula”. Radiation emitted by the white dwarf will interact with the gases of the nebula causing it to emit light at different wavelengths.

What’s odd about nebulae is that, since they come from the outer shell of a star, one would expect them to be spherical. And yet they are not. They come in many different shapes.

The reasons behind these shapes can be different, binary stars (two stars orbiting around each other) or planets orbiting the star could be a couple of these reasons. The gases of the nebulae vary; there is hydrogen but there can also be oxygen, sulfur and nitrogen. These gases emit in different colors of the spectrum. This is also why nebulae have such different colors. As nebulae came from the blowing away of the stars outer shell, they don’t remain still, they keep expanding. After a few thousands of years, they become very faint to observe. Their short life time is the reason why there are not so many of them on the sky. However, the size, color and shape of a nebula can tell us a lot about the life and death of the original star.

When stars between 8 and 20 solar masses eventually stop producing energy through fusion, they don’t simply have their core exposed after their outer shell is detached. The phenomena taking place here are so extreme, they cause the star to collapse under its own gravity and explode. What remains is a core that has undergone so many extreme changes that is truly extraordinary. The gravity in the remains of the core of such stars is so huge that it overcomes electron degeneracy (which occurs in white dwarfs) and literally force electrons to smash into protons thus creating neutrons. Very few of them survive. So, what really remains, is a supermassive object made of neutrons with some protons, electrons and element left here and there. These objects also have a thin crust of heavier elements nuclei, like iron and electrons. Imagine something like a gigantic atomic nucleus. These are the “Neutron Stars”. Neutron stars are among the most bizarre objects of the Universe. They have a radius of about 20 km and the mass of an entire star. To understand how insanely massive these objects are, imagine that a cough drop of neutron star material would weigh as much as all humans on Earth combined.

Neutron stars (also called pulsars) also spin very rapidly (a few times per second) and they emit very accurate pulses.  The pulses they emit are so accurate and consistent that when first detected scientists believed it was not coming from a natural object but from extra-terrestrial life.

Think about introducing neutron stars to your students when you talk to them about atomic nuclei, the strong and weak interaction!

For stars beyond 20 solar masses, the fate of a star is even more extreme. The gravity in such dying stars is so massive that nothing can stop it. After the star explodes it leaves behind what we call a“Black Hole”. A black hole, has such tremendous gravity that nothing can escape, it not even light. That’s why it’s black. In other words, the escape velocity* of a black hole is greater than the speed of light. Since not even light can escape a black hole, we can never really see it. The area around the black hole were the escape velocity is equal to the speed of light is called the “Event Horizon”. Nothing escapes once it passes that horizon. Black holes come in different sizes. The smaller can have as much as 3 solar masses. Unlike what some might thing they don’t suck all mass around it. Depending on the distance of an object from it, the object can actually orbit a black hole without being sucked in. However, if the object gets close enough, then it can indeed be pulled in by the black hole. It is believed that galactic centres are occupied by black holes and they could be playing a significant role in the evolution of galaxies.

As you may imagine, such staggering objects as black holes, also have very peculiar properties. For example, remember tides? In an earlier module we talked about how the Moon’s gravity affects the Earth and how tidal forces tend to stretch objects. Well, imagine what happens near an object with gravity so massive as a black hole’s! If an object like a tree was to fall in a black hole roots first, the gravity at the roots would be millions of times stronger than at the top of the tree, stretching it out to a thin line. And let’s not also forget about space-time! Gravity can affect space-time. The greater the gravity the slower time passes by. In fact, it slows down so much that at the event horizon it stops completely. So if we were standing near a black hole watching our tree pass the event horizon, time would freeze! We would watch the tree slowing down more and more taking infinite time to reach the horizon.

Our students’ perception of gravity is usually limited up to the point of gravity holding planets together around their parent star. Black holes, like white dwarfs and neutron stars are excellent examples, to demonstrate to your students how powerful gravity can be in extreme situations.

When stars bigger than 8 solar masses come to a point when they can no longer produce energy through fusion the go out with a tremendous explosion and become either neutron stars or black holes. The explosions of these stars are called “Supernova”. In fact this is only one type of supernova. A white dwarf can also cause a supernova when it’s part of a binary system of stars. The white dwarf will take mass from its companion and when it has accumulated enough mass it will collapse under its own gravity causing a supernova. Supernovae release unforeseen amounts of energy in a very short amount of time, at speeds close to the speed of light. They enrich the interstellar medium with heavy elements. In fact, we wouldn’t be here if it wasn’t for supernovae. Perhaps you noticed earlier that even the largest of stars can fuse elements only reaching up to iron. Iron is the ultimate form of ash in the Universe. That’s because fusion beyond iron is not producing any energy, it requires more energy than it emits. Thus stars can’t fuse iron to produce energy. Particles beyond iron can only produce energy through fission. So if it wasn’t in the interest of stars to make all the other elements, how did they come to exist? The calcium in our bones? Gold? Platinum?

During supernovae, conditions are so extreme that fusion takes place even if it’s not in the benefit of the exploding star thus creating heavier elements. These heavier elements are also scattered through the interstellar medium during the blast of a supernova. Eventually, over long periods of time, gas and dust that make up new stars and their planets are enriched by these heavier elements that were created during supernovae explosions.  Bottom line? We are all made of stardust!

When introducing the periodic table, binding energy, fusion and fission in class, talking about supernovae and how these elements came to exist can be very inspiring for your students and give them an idea of how tightly our lives are bound to the Universe and the stars.

Throughout all modules, we’ve talked about many space missions. As you can imagine none of these missions would exist if not for the people who designed, tested and eventually built these mind-boggling, complicated, high-tech instruments and pieces of equipment.  Engineering is a key pillar in the business of studying the Universe. We could put them all under one name, say “Aerospace Engineers”, but like in astronomy there are many different categories and specializations. For example, some engineers focus on testing the aerodynamics of aircrafts while others focus on propulsion systems, or material strength and behavior. There are space system engineers, material engineers, ground segment support engineers and many others different careers in this field. Like scientists, engineers also specialize on different branches through their studies. Many different types of engineers could have the same basic degree and start focusing their studies on specific branches at a later stage. When looking at the official website of a mission, there is always a part that presents the team of the mission. Having a look at the people working on a mission and their background could be inspirational for students and could help them get some more ideas.  In the videos below, you can get some more information and inspiration to present career role models in your classroom.

Objects like galaxies and nebulae can be ideal subjects if you are thinking of mixing art with science. You can inspire your students by getting them to created amazing images of galaxies or the milky was very easily using watercolors. Here is an example tutorial: