Nature’s Captivating Light Show

Auroras are some of the most beautiful and mysterious phenomena in the atmosphere. For millennia, humans have gazed up at the night sky in wonder at these seemingly magical lights. This extraordinary illumination populates the myths of civilizations across the globe. In Europe and China, it is often said that the aurora is at the root of legends of dragons and other mythological creatures. The North American Inuits attach a religious significance to auroras, which occur very frequently in northern Canada.

Auroras’ formation begins with the Sun approximately 149 million kilometers (93 million miles) away. At the center of our solar system, this celestial body is essentially a huge ball of hydrogen and helium held together by its own tremendous gravitational pull. The Sun generates light and heat through a process called nuclear fusion. Individual hydrogen atoms travel at high speeds in the Sun and occasionally collide into each other. When a collision happens, one of the hydrogen atoms turns into a neutron and combines with the other, forming the heavy isotope of hydrogen, deuterium. Then, this isotope combines with another hydrogen proton to form helium-3, the light isotope of helium. Lastly, two helium-3 isotopes combine to form a stable helium isotope (helium-4).

Since an isotope of helium-4 has less mass than four protons of hydrogen, this reaction causes the Sun to generate thermal and electromagnetic energy. The surface temperature of the Sun is so hot (a scorching 5,500°C/9,932°F) that many particles travel fast enough to escape the Sun’s surface and fly through space at speeds reaching up to 1000 kilometers (or 621 miles) per second. At such high temperatures, electrons escape from atoms, and the gas turns into plasma, the fourth state of matter. Generally speaking, plasma consists of an ionized gas composed of different types of particles.

This plasma, known as the solar wind, travels in many directions, but sometimes it moves towards the Earth. Fortunately, our planet has a strong magnetic field that deflects the solar wind. Most of these charged particles bounce away from the Earth back into space, but a small minority are redirected towards the magnetic poles of the Earth. That is why we can only see auroras in polar regions such as Canada, Scandinavia, or Antarctica. Auroras occur when the solar wind interacts with the Earth’s atmosphere. Specifically, they are the product of a chemical reaction between the charged ions present in the solar wind and the neutral atoms of our atmosphere. Auroras come in many different colors. The main cause behind this variance is the height at which the solar wind comes in contact with the Earth’s atmosphere. In fact, there is a relationship between the height and the wavelength of the emitted electromagnetic wave: the auroras occurring at the highest altitudes are shades of red (very infrequent), then slightly lower we see yellow, then green, and at the lower altitudes we see blue. The reason why there are different wavelengths has to do with the gasses in our atmosphere and solar activity. The air we breathe is composed mostly of nitrogen and oxygen (about 78% nitrogen and 21% oxygen). Due to the chemical properties of these gasses, when particles of the solar wind interact with oxygen, the reaction emits shades of green, while with nitrogen it emits shades of blue. High solar activity also influences the aurora’s color. Solar flares are tremendous bursts of energy at the Sun’s surface caused by a dramatic variation in the Sun’s magnetic field. This release of energy creates a particularly strong solar wind which generally gives rise to red auroras. In North America, auroras can appear anytime from mid-August through April.

Astronomers have observed auroras on other planets as well. The gas giants (Jupiter, Saturn, Uranus, and Neptune) all have a magnetic field and an atmosphere; thus, it is not surprising that the same mechanism functions on other celestial bodies. Since these planets have a stronger magnetic field than Earth, auroras can be considerably larger, as shown here. Much still remains a mystery about the cosmos, but our knowledge of auroras and their causes aid us in further comprehending the vast mysteries of the universe. With the increasing developments in space exploration and planetary colonization, understanding the interactions between astronomical phenomena is of paramount importance.