Aurora

To understand the occurance of Aurora Borealis (northern lights) and Aurora Australis (southern lights), we need analyze the activity of the Sun, the star at the center of our solar system. It has a diameter of 865,000 miles and mainly composed of hydrogen and helium. The Sun by constant nuclear fusion, is a spherical plasma heated to incandescence with a yellowish white surface and its core at a temperature of 29,000,000° F. The distance from Sun to Earth is about 93 million miles.

Aurora Borealis as seen from ISS (Photo Courtesy: NASA)		The surface of the Sun goes through magnetic fluctuations in cycles. Some areas on the Sun's surface will have 2500 times higher magnetic field than surrounding areas. Due to higher magnetic field, light does not pass through such areas and typically are referred to as Sun Spots, resulting in intense heat build up. The size of sun spots can be bigger than the diameter of our Earth. This built up of heat and magnetic field on the photosphere of the Sun causes Coronal Mass Ejection (CME). These solar flares or streams of plasma (ionized gas), emit magnetic fields and x-rays into space as geomagnetic storms. When the geomagnetic storms interfere with Earth's magnetic field in the ionosphere (60 to 80 miles above Earth), typically in the 55 to 80° (North/South latitude), it results in ions to glow and light up the sky in a display of special colors, commonly known as Aurora Borealis (Northern Lights).

Aurora Australis as seen from Space Shuttle (Photo Courtesy: NASA)		In the Southern hemisphere, the bright lights caused by geomagnetic storms is known as Aurora Australis (Southern Lights). The intensity of the geomagnetic storms has significant impact on the Earth's atmosphere, and satellites that orbit the Earth. When the intensity of the geomagnetic storm is very high, it can disrupt the communication of GPS, telecommunication or other satellites used for scientific purposes due to electromagnetic interferernce.

CME on July 23^rd, 2012 (Photo Courtesy: NASA)

Various research agencies and the Solar research agency of NASA, Solar Dynamics Observatory (SDO) constantly monitor solar activity for Sun Spots and changes occuring on the Sun's surface. This helps in predicting geomagnetic storms that may reach the Earth and its effects on the Earth, the weather pattern, satellites and communication blackouts that could occur. On September 1^st 1859, there was an extremely massive geomagnetic storm that caused telegraphic blackouts and display of bright lights (Aurora Borealis and Aurora Australis) in most parts of the Earth (lower latitudes). This is known as Carrington Event (IAU designation of SOL1859-09-01), named after British astronomer Richard Carrington. The Solar storm may occur for few minutes to several hours, but its impact on Earth's magnetoshpere can last for days to several weeks.

The Sun being a sphirical ball of plasma, will have Sun Spots in cycles and that creates intense geomagnetic storms (solar flares) during these cycles. The solar flares (CME) get ejected into deep space away from the Earth's orbit from time to time. If such a intense geomagnetic storm were to impact the Earth, it will result in losses and mayhem in global scale due to massive disruption of activites on Earth. It takes about 8 minutes and 19 seconds for light to travel from Sun to Earth (93 million miles). As the Earth is rotating around the Sun, based on the intensity of the Solar flare, it will have impact on major parts of the Earth. This type of instense storm occurred on July 23^rd, 2012 and per astronomical calculations, the Earth was nine days away from stream of impact and the CME was blown away into deep space, averting major havoc on Earth.

Distance Travelled By Earth Daily

The total orbital distance travelled by the Earth around the Sun in one year is about 940 million km. In a single day we travel a massive 2.573 million km (2,573,537.46 km). This explains how we all were lucky to miss the (possible Carrington like event) geomagnetic storm of July 23^rd, 2012 by 23.161 million km (23,161,837.18) a distance gap of the Earth from the stream of the storm (about 9 days off).