Aurora occurs when charged particles from the Sun disrupt the Earth’s magnetic field, and thus can penetrate the atmosphere. Usually, the charged particles deflected by the magnetic field into space, and that protects us.

When charged particles enter the atmosphere at high altitude (around 250km), they can with their high energy excitation of atoms and molecules: these electrons are placed in other jobs or even thrown out of the atom (ionization). In recombination and de-excitation is a surplus of energy in the form of light emitted. This light is what we see as auroras. The color of the light varies depending on the type of atom or molecule and the energy of the electron orbits.

The charged particles are in space around the Sun, but have a high concentration and speed when the sun has an eruption (called a Coronal Mass Ejection, or CME). These eruptions caused by “magnetic circuit” in sunspots. The magnetic field lines in sunspots are sometimes very complex, and become unstable. When the field is suddenly short-circuited, are massive amounts of energy which is then an explosion on the surface of the sun damage. The particles (mostly protons) that are ejected into space this may arrive at the earth as the explosion on the side of the sun we see.

Every 11 years, activity on the Sun called a ceiling. There are a few more years on average, heavier bursts. The chance of auroras in this period also increased, and, in addition to lower latitudes. Normally only aurora around and above the Arctic circle to see (both south and north). The last maximum was around 2000-2001 and several times in the Netherlands has yielded spectacular auroras. The following minimum in 2006, although in 2004 and 2005 the aurora also occasionally been seen in the Netherlands. The attentive observer will on average once a year or Northern Lights can be seen in the Netherlands, and once every 3 or 4 years spectacular auroras.

Observing aurora

The weak form of auroral manifests itself as a green belt on the northern horizon. If the aurora is active, you often see a red glow, and if it has been more active in this pink, red, purple or bluish rays to see. These rays move fast, but usually not as fast as you can see them visibly change. Often when a weak form of aurora is visible, it can suddenly from one minute to another “flare up”. If there is any form of aurora over the Netherlands to see, so if possible you should keep looking all night. Many observers in the Netherlands went to bed after hours of inactivity, to later read on the Internet that it was very spectacular half hour of sleep. It’s really about as dawn commitment, because you can not perceive!

The different colors of the aurora caused by the different gases in the atmosphere. Aurora is at altitude to see, from roughly 80 km above 200 km. At these altitudes, the gases in the atmosphere is not mixed, but stratified to specific gravity. Green and red caused by oxygen (O), but red can be less than the green caused by nitrogen (N). Nitrogen can also cause a pink glow. Blue aurora is rare and occurs when the aurora is so active that hydrogen (H) is struck.

The great geomagnetic storms caused by CMEs often cause large-scale auroral extending far towards the equator can be seen as the aurora over the Netherlands on 7 April 2000. This aurora was in Italy to see.

Photography

To aurora to shoot you use a fast film, such as 400 or 800 ISO. Better to use a digital SLR if you slightly lower resolution compared to film is no objection. Wide angle lenses are well suited, because it allows you a large portion of the air picture. Active aurora is vast, and the whole phenomenon can only be whole picture with a fish-eye lens.

Use a fairly large aperture like f/2.8 or f / 4, but prefer not to use the widest aperture of the lens to prevent vignetting (where the corners of the image darker). Usually you do a few seconds with fast film (up to 10 or 20 seconds) long exposure. If you need longer exposure, the aurora may be slightly washed out, because it changes.

A digital camera has the advantage that you can control the exposure time directly by looking at the result. The very best for a digital camera and a film camera to use. The digital camera do you use this as an exposure indicator, and the film for serious high-resolution pictures.