Milky way
The galaxy of which the sun and the solar system are a part and which contains the myriads of stars that create the light of the Milky Way.It is a barred spiral galaxy with a diameter between 150,000
and 200,000 light-years. It is estimated to contain 100–400 billion stars and
more than 100 billion planets.
Changes in earths orbits in the past
On January 3rd, 2019, Earth reached the point in its orbit
where it's at its closest approach to the Sun: perihelion. Every object
orbiting a single mass makes an ellipse, containing a point of closest approach
that's unique to that particular orbit, known as periapsis. For the past 4.5
billion years, Earth has orbited the Sun in an ellipse, just like all the other
planets orbiting their stars in all the other mature solar systems throughout
the galaxy and Universe.
Earth's orbital path doesn't remain the same over time, but
spirals outward. This year, 2019, our perihelion was 1.5 centimeters farther
away than it was last year, which was more distant than the year before.
If the central mass were unchanging, and were the only
factor at play, the force of gravity would remain constant over time. Every
orbit would continue in a perfect, closed ellipse forever, and would never
change.
Just 800 years ago, perihelion and the winter solstice
aligned. Due to the procession of Earth's orbit, they are slowly drifting
apart, completing a full cycle every 21,000 years.
Factors that alter orbits
Ø The additional curvature of space-time due to General Relativity, which causes planets near to a large mass to undergo additional procession,
Ø The presence of matter particles in the plane of the Solar System, which causes drag on the planets and creates an in spiraling phenomenon,
Ø The creation of gravitational waves, which is what happens when any mass (like a planet) passes through a region where space-time curvature is changing (such as near a star), also causing an in spiral.
How is it spiraling?
Overall, the Earth isn't even spiraling in toward the Sun;
it's spiraling outward, away from it. So are all the planets of the Solar
System. With every year that goes by, we find ourselves just slightly — 1.5
centimeters, or 0.00000000001% the Earth-Sun distance — farther away from the
Sun than the year before.
As time goes on, the helium-containing region in the core
expands and the maximum temperature increases, causing the Sun's energy output
to increase.
Every second, the Sun emits some 3.846 × 1026 joules of
energy, which are released via the conversion of mass into energy in the core.
Einstein's E = mc2 is the root cause, nuclear fusion is the process, and the
continuous emission of energy from the Sun is the result. This energy is the
underlying process that powers practically every biologically interesting
process occurring on Earth.
On a year-by-year basis, the Sun loses some 4.7 million tons
of matter, which lessens the gravitational pull on every object in our Solar
System. It's this gravitational pull that causes our orbits to behave as we
know them to behave.
Observations using the Atacama Large
Millimeter/sub-millimeter Array (ALMA) have revealed an unexpected spiral
structure in the material around the old star R Sculptoris. This feature has
never been seen before and is probably caused by a hidden companion star
orbiting the star, one of the many unexpected scientific results to emerge from
ALMA. In general, unexpected results can be harbingers of new physics or
physical systems, and are often the most interesting results nature has to
offer.
In the case of the Solar System, though, it would be a shock
if the Earth and all the planets weren't spiraling away from the Sun. The story
of why we must be spiraling away from the Sun is so simple and compelling that
it's impossible to ignore.
