Auroras

                                   Aurora 

     An aurora is a natural phenomenon which is characterized by a display of a natural-coloured (green, red, yellow or white) light in the sky.

    An aurora is a colorful light show in the sky caused by the Sun. Auroras happen when particles from the Sun interact with gases in our atmosphere, causing beautiful displays of light in the sky. Auroras are often seen in are as near the North Pole or South Pole.

What Makes This Happen?

    Even though auroras are best seen at night, they are actually caused by the Sun. The Sun sends us more than heat and light; it sends lots of other energy and small particles our way. The protective magnetic field around Earth shields us from most of the energy and particles, and we don't even notice them.

    But the Sun doesn't send the same amount of energy all the time. There is a constant streaming solar wind and there are also solar storms. During one kind of solar storm called a coronal mass ejection, the Sun burps out a huge bubble of electrified gas that can travel through space at high speeds. When a solar storm comes toward us, some of the energy and small particles can travel down the magnetic field lines at the north and south poles into Earth's atmosphere. There, the particles interact with gases in our atmosphere resulting in beautiful displays of light in the sky. Oxygen gives off green and red light. Nitrogen glows blue and purple.

Do Other Planets Get Auroras 

        They sure do! Auroras are not just something   that happen on Earth. If a planet has an atmosphere and magnetic field, they probably have auroras. We've seen amazing auroras on Jupiter and Saturn.

Forms Of Auroras :

1. A mild glow, near the horizon. These can be close to the limit of visibility, but can be distinguished from moonlit clouds because stars can be seen undiminished through the glow.
2. Patches or surfaces that look like clouds.
3. Arcs curve across the sky.
4. Rays are light and dark stripes across arcs, reaching upwards by various amounts.
5. Coronas cover much of the sky and diverge from one point on it.

Types Of Auroras : 

1. STEVE

   In 2016, more than fifty citizen science observations described what was to them an unknown type of aurora which they named "STEVE", for "Strong Thermal Emission Velocity Enhancement". STEVE is not an aurora but is caused by a 25 km (16 mi) wide ribbon of hot plasma at an altitude of 450 km (280 mi), with a temperature of 6,000 K (5,730 °C; 10,340 °F) and flowing at a speed of 6 km/s (3.7 mi/s) (compared to 10 m/s (33 ft/s) outside the ribbon).

2. Picket-fence aurora

   The processes that cause STEVE also are associated with a picket-fence aurora, although the latter can be seen without STEVE. It is an aurora because it is caused by precipitation of electrons in the atmosphere but it appears outside the auroral oval,closer to the equator than typical auroras. When the picket-fence aurora appears with STEVE, it is below.

3. Dune aurora

   First reported in 2020 and confirmed in 2021 the dune aurora phenomenon was discovered by Finnish citizen scientists. It consists of regularly-spaced, parallel stripes of brighter emission in the green diffuse aurora which give the impression of sand dunes. The phenomenon is believed to be caused by the modulation of atomic oxygen density by a large-scale atmospheric wave travelling horizontally in a waveguide through an inversion layer in the mesosphere in presence of electron precipitation.

    Colors And Wavelengths Of Auroras:

1. Red: At its highest altitudes, excited atomic oxygen emits at 630 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under more intense solar activity.                                                                                                                           
2. Green: At lower altitudes, the more frequent collisions suppress the 630 nm (red) mode: rather the 557.7 nm emission (green) dominates. A fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common.                                                         
3. Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant.

   Causes :

1. Geomagnetic disturbance from an enhanced solar wind causes distortions of the magnetotail ("magnetic sub storms").
2. Acceleration of auroral charged particles invariably accompanies a magnetospheric disturbance that causes an aurora.
3. A quiescent solar wind flowing past Earth's magnetosphere steadily interacts with it and can both inject solar wind particles directly onto the geomagnetic field lines that are 'open', as opposed to being 'closed' in the opposite hemisphere, and provide diffusion through the bow shock.

What is the aurora used for?    

    Auroras, also called the "polar lights," are rarely visible outside 70 degrees north and south latitudes. An aurora is a natural light display that shimmers in the sky. Colorful blue, red, yellow, green, and orange lights shift gently and change shape like softly blowing curtains.

How Often Do Auroras Happen ?

"Active periods are typically about 30 minutes long and occur every two hours, if the activity is high. The aurora is a sporadic phenomenon, occurring randomly for short periods or perhaps not at all."

 

Whether it’s in our own backyard or millions of light-years away, the universe can get pretty weird.