What is an Aurora?

Aurora is the glow or light produced when electrons from space flow down Earth’s magnetic field and collide with atoms and molecules in the upper atmosphere. This interaction creates light, similar to how neon lights work.

What are the Northern and Southern Lights?

The aurora is called the Northern Lights (Aurora Borealis) in the northern hemisphere and the Southern Lights (Aurora Australis) in the southern hemisphere. The term ”Aurora” comes from Latin and was first used by Galileo, named after the goddess of dawn. ”Borealis” means ”northern,” while ”Australis” means ”southern.”

What Causes the Aurora?

Auroras form due to interactions between the solar wind from the sun and Earth’s magnetic field (magnetosphere). When solar wind speeds increase and the interplanetary magnetic field turns southward, geomagnetic activity rises, making auroras brighter and more active.

What is the Kp index, and why does it matter?

The Kp index measures geomagnetic activity on a scale from 0 to 9. Higher Kp values mean the aurora can be seen further from the poles:

• Kp 0-2: Aurora is dim and far north.
• Kp 3-5: More active, brighter, and further south.
• Kp 6-7: Visible in the northern U.S.
• Kp 8-9: Very bright, reaching further towards the equator.

How does the Kp index affect auroral latitude?

For every Kp level increase, the aurora moves about 2 degrees closer to the equator. At Kp = 9, the aurora can reach around 48 degrees magnetic latitude.

What are the key factors for viewing the aurora?

There are four important factors to consider:

1. Geomagnetic Activity – The strength and location of the aurora depend on solar activity and the planetary K index (Kp), which ranges from 0 to 9.
2. Location – The closer you are to the magnetic poles, the better your chances of seeing the aurora.
3. Darkness – Light pollution and the full moon can reduce visibility.

Where should I go to see the aurora?

Sweden, Finland, Norway, Iceland, Canada, Alaska, Svalbard or Greenland, around or above the Arctic circle. Towards the magnetic poles. The north magnetic pole is currently in northeastern Canada. An unobstructed view to the north (or south in the Southern Hemisphere) helps. Elevated locations, away from city lights, are ideal.

What is the best time of night to see the aurora?

The most active period is usually between 10 PM and 2 AM local time. However, as geomagnetic activity increases, the aurora may be visible earlier in the evening and later into the morning.

What are the best seasons to see the aurora?

The best times are around the spring and fall equinoxes. Geomagnetic storms are more frequent during these periods, creating better aurora displays. However, keep in mind that northern regions experience long daylight hours in summer, making aurora viewing difficult.

What Solar Events Create Strong Auroras?

Two major solar events can trigger intense auroras:

1. Coronal Mass Ejections (CMEs): These are massive bursts of plasma ejected from the sun, traveling at high speeds. When a CME reaches Earth, it can cause strong geomagnetic storms and bright auroras extending far from the poles.
2. Coronal Holes: These are regions on the sun where high-speed solar wind streams originate. When these streams reach Earth, they can create moderate geomagnetic storms and auroras, though less intense than those from CMEs.

Where Do Auroral Electrons Come From?

Although the solar wind influences auroras, the electrons that create auroras originate within Earth’s magnetosphere. When solar wind energy transfers into Earth’s magnetic field, it accelerates these electrons downward, producing the auroral display. The electrons responsible for the best auroras at night typically come from the magnetosphere’s tail, downstream from the sun.

Does light pollution or the moon affect aurora visibility?

Yes! City lights and a full moon can diminish the apparent brightness of the aurora. For the best experience, go to a dark area with minimal light pollution.

Can I see the aurora even if I’m far from the poles?

Yes! When geomagnetic activity is high (Kp 6+), the aurora can be visible from the northern U.S. and even further south in rare cases.

How is the Aurora Created?

When fast-moving electrons, traveling nearly 1/10th the speed of light (20,000 km/sec or 44 million mph), collide with atoms and molecules in Earth’s upper atmosphere (above 100 km or 60 miles), they transfer energy to the atmosphere. This process ”excites” the atoms or molecules to higher energy states. As they relax back to their natural energy levels, they release photons. These photons are what we see as the aurora. This process is similar to how neon or fluorescent lights work.

What is the Relationship Between Geomagnetic Activity and Aurora?

The aurora is one manifestation of geomagnetic activity. The electrons that create the aurora also carry electric currents through the ionized portion of the upper atmosphere (the ionosphere). These currents generate perturbations in the magnetic field at Earth’s surface. These changes in the geomagnetic field are measured and used to create geomagnetic disturbance indices, such as the Planetary K index (Kp).

Kp is a reliable indicator of aurora activity:

• Kp 7 to 9: The aurora is bright, and the auroral oval moves to lower latitudes.
• Kp 5 to 6: The aurora retreats towards the poles, is less bright, and less active.
• Kp 3 to 4: The aurora is closer to the magnetic poles but still visible with reasonable brightness and activity.

Why Does the Aurora Have Different Colors?

The different colors of the aurora are produced when different atmospheric atoms and molecules are excited to various energy levels. The most common auroral color is a pale green at a wavelength of 557.7 nm, caused by atomic oxygen being excited to the 1S (singlet S) state. A deep red color comes from atomic oxygen excited to the 1D (singlet D) state. Other colors, such as purples and blues, come from nitrogen molecules.