The Sun –Energy for Life
The Sun is the star at the center of the Solar System, the most important
source of energy for life on Earth. The sun is a sphere of hot plasma, with
internal convection currents that generate a magnetic field. Its diameter is
109 times that of Earth and its mass is 330,000 times bigger than earth’s.
Three quarters of the Sun's mass consists of hydrogen (73%), the rest is mostly
helium (25%), with smaller quantities of oxygen, carbon, neon, and iron.
The sun’s energy output is created by hydrogen fusion that creates electromagnetic
radiation and helium. The Sun has an absolute magnitude of +4.83, estimated to be brighter than about
85% of the stars in our galaxy, most of which are red dwarfs. The sun rotates
and releases energy in all frequencies of the electromagnetic spectrum. The
surface is turbulent with moving sunspots, solar flares and coronal mass
ejections. High-speed streams of solar wind are emitted from coronal holes. Both
coronal-mass ejections and high-speed streams of solar wind carry plasma and an
interplanetary magnetic field outward into the Solar System. The surface
temperature of the photosphere is approximately 6,000 K, but surprisingly the
temperature of the surrounding corona reaches 1,000,000–2,000,000 K.
The Earth orbits around the sun on a tilted axis. Between September and
March, Earth’s Northern Hemisphere gets less exposure to direct sunlight
over the course of a day. The rest of the year, the north gets more direct
sunlight and the Southern Hemisphere gets less. The winter solstice
occurs when the sun is directly over the Tropic of Capricorn, or 23.5° south
latitude. In 2017, this occurred at 11:28 am Eastern time on
December 21, 2017.
In December 2017, NASA launched an instrument to the
International Space Station to continue monitoring the Sun’s energy input to the
Earth system. The Total and Spectral solar Irradiance Sensor (TSIS-1) will
precisely measure what scientists call “total solar irradiance.” These data will
give us a better understanding of Earth’s primary energy supply and help improve
models simulating Earth’s climate. The input from the Sun is just one of many
factors scientists used to model Earth’s climate. Earth’s climate is also
affected by other factors such as greenhouse gases, clouds scattering light and
small particles in the atmosphere called aerosols — all of which are taken into
account in comprehensive climate models.
Patel wrote:” The Sun’s output
energy is not constant. Over the course of about 11 years, our Sun cycles from a
relatively quiet state to a peak in intense solar activity — like explosions of
light and solar material — called a solar maximum. In subsequent years the Sun
returns to a quiet state and the cycle starts over again. The Sun has fewer
sunspots — dark areas that are often the source of increased solar activity —
and stops producing so many explosions, going through a period called the solar
minimum. Over the course of one solar cycle (one 11-year period), the Sun’s
emitted energy varies on average at about 0.1 percent. That may not sound like a
lot, but the Sun emits a large amount of energy – 1,361 watts per square meter.
Even fluctuations at just a tenth of a percent can affect Earth.” (Kasha Patel.
Four decades and counting: New NASA instrument continues measuring solar energy
input to Earth NASA Goddard Space Flight Center. Nov 28 2017.)
Despite the sun’s obvious turbulence, animals and plants on earth humans have
depended on its relative stability. A recent and serious concern is that the sun
can produce magnetic storms that would disable or destroy our electric grids
and electronics. Most solar disturbances are reflected by our magnetic field or
absorbed by the atmosphere. However, infrequent large events can be anticipated.
Geomagnetic storms have caused solar energetic Particle (SEP) events, geomagnetically induced currents (GIC), ionospheric disturbances that cause
radio and radar scintillation, disruption of navigation by magnetic compass and
auroral displays at much lower latitudes than normal. In 1989, a geomagnetic
storm energized ground induced currents that disrupted telegraph networks,
electric power distribution and caused aurorae as far south as Texas. NASA
operates continuous sun observations. Their understanding of solar flares is
advancing. NASA described:” Solar flares are intense bursts of light from the
sun. They are created when complicated magnetic fields suddenly and explosively
rearrange themselves, converting magnetic energy into light. During a December
2013 solar flare, three solar observatories captured the most comprehensive
observations of an electromagnetic phenomenon called a current sheet. These
eruptions on the sun eject radiation in all directions. The strongest solar
flares can impact the ionized part of Earth’s atmosphere – the ionosphere – and
interfere with our communications systems, like radio and GPS, and also disrupt
onboard satellite electronics. Additionally, high-energy particles – including
electrons, protons and heavier ions – are accelerated by solar flares.