If you’ve ever fallen down the rabbit hole of travel photography, you’ve probably come across a few pictures of a wintry night sky lit up with fluorescent trails. This naturally occurring phenomenon is known as the Northern Lights. You might have been left wondering how this event happens, or why it takes place. Well, we’re breaking the whole thing down in this crash course in the Northern Lights.

What are the Northern Lights?

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The official term for the Northern Lights is Aurora borealis and it’s more about a natural chemical reaction that occurs in our atmosphere rather than some mystic event. This reaction tends to occur near the earth’s north and south poles, which are magnetic. The evening light shows can appear in a variety of colors, but the most common are green and pink. However, don’t be surprised if you witness violet, red, and even blue auroras.

The size and shape of the light show can also vary—ranging from streamers to arcs, patches, and even complete clouds. Suitably, the Northern Lights occur in the Northern Hemisphere. However, it’s important to note that even though the Northern Lights get all the attention, this natural event also takes place in the Southern Hemisphere, where it's called the Aurora australis or Southern Lights.

What causes this event?

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Every day, Earth is bombarded with electrically charged particles that are released during solar flares and escape the sun’s magnetic field. Typically, the Earth’s own magnetic field can protect our atmosphere from the bulk of these particles. But the field is weakest at the north and south poles. So, on some occasions, these solar particles are able to penetrate our field and collide with gas particles that are naturally found in our atmosphere. The chemical reaction that occurs between the charged solar particles and the atmosphere’s gas particles create those colors we mentioned earlier.

The color released is dependent upon the type of gas-particle involved in the reaction. In case you weren’t aware, there’s more than oxygen in our atmosphere. For example, the common green hue often seen during the Northern Lights is caused by reactions with oxygen. However, oxygen can produce more colors depending on the altitude of the collision. Reactions that take place at lower altitudes (roughly 60 miles above the earth’s surface) will release the typical green hue mentioned earlier. However, high altitude collisions such as 200 miles above the surface, can produce a rare red shade. Typically, all Northern Light collisions can occur between 50 to 400 miles above the Earth’s surface.

When is the best time to see the Northern Lights?

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While auroras could happen at any time because it’s a chemical reaction between solar and gaseous particles, the Northern Lights are typically limited to autumn through early spring with winter being the optimal time for viewing. But depending on your location, you can catch the light show between September and early April. During the winter, nights are longer, meaning you’ll have more time to see the auroras. Astronomers recommend midnight viewing as the best time to spot the lights because the sky will be at its darkest level.

However, if you live in the Southern Hemisphere, winter will be a different time frame for you. The seasons are reversed between hemispheres, so your ideal time to view the Southern Lights is March through September, depending on the location. Regardless of whether you view the Northern or Southern Lights, keep an eye on the weather forecast as you won’t be able to catch either phenomenon on a cloudy evening.

Where are the best places to watch the Northern Lights?

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As a general rule, anywhere dark and rural is preferred over city viewing. For obvious reasons, light pollution from buildings, signs, or even street lights will diminish your chances of seeing the Northern Lights with the naked eye. However, you don’t always have to be in far north locations. For example, people in places as far south as Louisiana and Mexico have confirmed seeing auroras. Still, these were in rural locations, not major cities or urban areas. Also, note that evenings with new moons (i.e. there’s no visible moon in the sky) are preferred over full moons because of the impact of light pollution.

If you’re planning a trip centered around the Northern Lights, it’s important to research when the light show is most likely to occur in the region you’re targeting. Your ability to catch the lights will depend on how far north a place is located and the amount of daylight they experience. For example, Alaska and Iceland are two very popular places that incorporate aurora viewing into their tourism because they both have very short periods of daylight in the winter. For Iceland, September through April is their core season for the Northern Lights. In contrast, Alaska’s high season is November through February with November, December and January listed as the best months.

So now you know that you might get lucky and see an aurora during any point in the year. But if you’re hoping to catch the Northern or Southern Lights, timing is everything. No matter which light show you're targeting, remember to avoid city viewing and be mindful of the weather forecast.