Northern Lights (aurora) and the Physics behind the show

03^rd Dec. 2025

Auroras are light emitted when charged particles (mostly electrons, also some protons) from the magnetosphere / solar wind are accelerated along Earth’s magnetic field lines and slam into atoms and molecules in the upper atmosphere. Those collisions excite the atoms, when the atoms de-excite they emits the colored light we see.

Step-by-step events behind Physics of Northern Lights

1. Source of particles : The Sun constantly emits the solar wind (a plasma). Sometimes it releases extra plasma in coronal mass ejections (CMEs) or fast streams. The magnetosphere (Earth’s magnetic bubble) intercepts this flow.

2. Magnetospheric dynamics & acceleration : Magnetic reconnection (dayside and in the magnetotail), turbulent fields, and wave particle interactions transfer energy from the solar wind into the magnetosphere and accelerate particles. Field aligned electric fields and Alfvén waves can further accelerate electrons down toward the poles.

3. Guided by the magnetic field : Charged particles spiral (gyrate) around magnetic field lines and travel along them toward higher magnetic field strength (toward the poles).

4. Precipitation and collisions : When those energetic electrons hit the neutral atmosphere (oxygen, molecular nitrogen), they excite and ionize atoms and molecules. The excited species later emit photons, the auroral light.

5. Observed shapes & dynamics : The magnetic-field geometry makes auroras appear as long arcs/curtains aligned roughly east–west (the “auroral oval”). Time variability (pulsations, flickers, substorm breakups) comes from changing acceleration processes in the magnetosphere.

Why different Aurora colors and altitudes?

Different excited states and different atmospheric species give different colors and come from different altitudes because of varying density and collisional quenching.

Common lines:

• Green (≈557.7 nm) : atomic oxygen. Often from ~100–150 km altitude. (Fast enough de-excitation to be bright; lifetime ~0.5–1 s in low density.)

• Red (630.0 nm) : atomic oxygen, produced higher up (~200–300+ km). The excited state responsible is long-lived (tens to hundreds of seconds), so red auroras are often diffuse and persistent.

• Blue / purple (≈427.8 nm bands and continuum) : molecular nitrogen and N2+ emissions, usually from lower altitudes (~80–120 km) where more energetic electrons penetrate.

• Hydrogen lines : (Hα) or proton aurora can appear when precipitating protons produce fast neutrals that excite hydrogen.

• Energy : Typical auroral electrons have energies from a few hundred eV up to tens of keV. Lower energies produce faint, high altitude emissions (reds); higher energies penetrate deeper and produce blues/purples and more structured curtains.

Different types of Aurora behaviors

• Substorms : sudden release of stored energy in the magnetotail causes brightening and fast breakup of the auroral oval.

• Flickering aurora : caused by wave–particle interactions (e.g., with electromagnetic ion cyclotron waves or chorus) modulating precipitation at tens of Hz.

• Pulsating aurora : on-times of seconds, linked to pitch-angle scattering of electrons by waves in the magnetosphere.

Best time of year to watch Northern Lights (aurora)

Main season: late September to early April (long, dark nights). Winter gives the most hours of darkness to hunt the lights.

Prime hours: roughly 10 PM to 2 AM local time (aurora activity typically strongest near local midnight).

Best places worldwide to watch Aurora

1. Alaska (Fairbanks / Anchorage / Denali / Brooks Range ) : USA.

2. Tromsø : Norway, very popular, high chances and many tours.

3. Abisko : Sweden, famed for the “blue hole” microclimate and clear skies.

4. Lofoten Islands : Norway, dramatic scenery + auroras over fjords.

5. Reykjavík : Iceland (and rural Iceland), easy access + many tour options.

6. Svalbard : Norway, extreme Arctic; aurora can be visible even at midday during polar night.

7. Yellowknife : Canada, one of North America’s most reliable spots (many aurora lodges).

8. Churchill / Manitoba : Canada, very frequent aurora nights, also wildlife combos.

9. Greenland : Very dark skies and high-latitude location.

10. Finnish Lapland : Easy winter tourism + glass igloos.

Even if you are a stargazer or a photographer, chasing the aurora rewards patience, preparation, and a little geomagnetic luck. Give yourself magnificent nights under dark, clear skies. When the light curtains of green, red, and violet finally unfurl, you won’t just witness a light show. You’ll see the Sun and Earth in beautiful, visible conversation.

Web Resources on Northern Light (Aurora)

1. Space.com: Stunning auroras are coming.
2. Nationalgeographic.com: 7 magical places to view auroras.
3. Nasa.com: What Causes Auroras?