what you have to learn is if you put a ball on a piece of string and then you spin around in circles..
you then although you have the string gravitationally linking you to the ball. cause the ball to orbit you
this centrifugal force on the ball tries to push the ball away from you, you feel the string tucking on your hand trying to get more distance which it gains if you loosened your hand a bit
if u had a drone recording this from above you would see the ball actually do a spiral.
if you imagine the orbit of earth around the sun as not a complete circle but instead a spiral. where each orbit, earth is slightly further away, allowing less gravitational power from sun, thus allowing earth to get further away on the next orbit
notice how the early loops (center) are small millimeter distances apart per cycle
then as the orbits continue the distance greatens each time
the sun does the same with its relationship with the milky way
and thats why we are increasing distance(increased radius) from the governing force(milky way->sun) (sun_earth)
enjoy that thought
there is a reason why they say the earth is 4.5 billion years old
because at a 1.5cm radius increase per year which is 0.00000000001% of todays earth-sun distance, it took the earth
billion of years to have, once cooled into a crusted rock billions of years to reach the distance earth has reached
but we are gaining more distance slowly (unnoticeable with the human eye even at the measure over a century)
but in the big cosmic measure of billions of years. they do say we are "speeding up" and moving further away at an accelerating speed
over 4.5billion years the sun has lost 0.03% of its mass via conversion to energy. which has meant it has less gravitational control compared to billions of years(it has loosened the string attached to the ball)
as for dark "matter" pfft..
in space there is no "matter" in the OPEN SPACE.. energy(plasma waves) is not formed into atoms yet* to become matter, it remains in its plasma state
think of all plasma as frequency waves of different frequencies..
we only have machines to view/observe/record only a certain range of frequencies magnetic spectrum of (sound-xray)
dark "matter" is just the plasma outside of out instruments ability.
and frequencies can do things to other things. like resist, refract, reflect... interfere ... coalesce, attract and so on
*the right type of frequencies need to interact with each other to cause different reactions. some of them can cause atoms to form and some do the opposite