I Can’t Sleep - Orbits | Calm Bedtime Reading for Sleep
Episode Date: March 2, 2026Drift off with calm bedtime reading about orbits, designed to ease insomnia and guide you into restful sleep. This soothing exploration blends peaceful learning with gentle narration, offering comfort... for sleeplessness and a quiet mind at bedtime. In this episode, Benjamin takes you on a slow, steady journey through the science of orbits, how planets circle stars, how moons travel around planets, and how gravity shapes the elegant paths of celestial bodies. You will discover the simple principles behind elliptical motion, orbital periods, and the delicate balance between speed and gravity, all presented in a way that feels grounding rather than overwhelming. There is no whispering, just fact filled, calm education delivered in Benjamin’s steady, reassuring cadence. As you learn about the predictable rhythms of space, your own thoughts may begin to settle into a more peaceful pattern. This gentle bedtime reading can help quiet anxiety, reduce stress, and provide steady mental focus for those experiencing insomnia or restless nights. Press play, get comfortable, and let the graceful movement of the cosmos carry you softly toward rest. Happy sleeping! Read with permission from Orbit, Wikipedia (https://en.wikipedia.org/wiki/Orbit), licensed under CC BY SA 4.0. Learn more about your ad choices. Visit megaphone.fm/adchoices
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Welcome to the I Can't Sleep podcast, where I help you drift off one fact at a time.
I'm your host, Benjamin Boster.
And today's episode is about orbits.
In celestial mechanics, an orbit is the curve.
trajectory of an object under the influence of an attracting force.
Alternatively, it is known as an orbital revolution
because it is a rotation around an axis external to the moving body.
Examples for orbits include the trajectory of a planet around a star,
a natural satellite around a planet,
or an artificial satellite around an object or position in space,
such as a planet, moon, asteroid, or Lagrange Point.
Normally, orbit refers to a regularly repeating trajectory,
although it may also refer to a non-repeating trajectory.
To a close approximation, planets and satellites follow elliptic or,
orbits, with a center of mass being orbited at a focal point of the ellipse, as described
by Kepler's laws of planetary motion.
For most situations, orbital motion is adequately approximated by Newtonian mechanics,
which explains gravity as a force obeying an inverse square law.
However, Albert Einstein's general theory of relativity, which accounts for gravity as due to curvature
of space-time, with orbits following geodesics, provides a more accurate calculation and understanding
of the exact mechanics of orbital motion.
Historically, the apparent motions of the planets were described by European and Arabic
philosophers using the idea of celestial spheres.
This model positioned the existence of perfect moving spheres or rings to which the stars
and planets were attached.
It assumed the heavens were fixed apart from the motion of the spheres and was developed
without any understanding of gravity.
This concept originated with Hellenistic astronomy.
particularly Udoxis and Aristotle.
After the planet's motions were more accurately measured,
theoretical mechanisms, such as deference and epicycles, were added by Ptolemy.
Although the model was capable of reasonably accurately predicting the planet's positions in the sky,
more and more epicycles were required as the measurements became more accurate.
Hence the model became increasingly unwieldy.
Originally geocentric, it was modified by Copernicus to place the sun at the center to help
simplify the model.
The model was further challenged during the 16th century as comets were observed traversing
the spheres.
The basis for the modern description of orbits was first formulated by Johannes Kepler.
whose results are summarized in his three laws of planetary motion.
First, he found that the orbits of the planets in the solar system are elliptical,
not circular, or epicyclic, as had previously been believed,
and that the sun is not located at the center of the orbits,
but rather at one focus.
Second, he found that the orbital speed of each planet is not
constant, as had previously been thought, but rather that the speed depends on the planet's distance
from the sun. Third, Kepler found a universal relationship between the orbital properties
of all the planets orbiting the sun. For the planets, the cubes of their distances from the sun
are proportional to the squares of their orbital periods. Jupiter and Venus, for example, are
respectively about 5.2 and 0.723 astronomical units distant from the sun.
Their orbital periods respectively about 11.86 and 0.615 years. The proportionality is seen by the fact
that the ratio for Jupiter 5.204 cubed divided by 11.862 squared,
is approximately equal to 1.002,
is practically equal to that for Venus.
0.7.23 cubed,
divided by 0.615 squared,
is approximately equal to 0.99.
In accord with the relationship,
idealized orbits meeting these rules are
known as Kepler orbits.
Isaac Newton demonstrated that Kepler's laws were derivable from his theory of gravitation,
and that in general the orbits of bodies subject to gravity were conic sections,
under his assumption that the force of gravity propagates instantaneously.
To satisfy Kepler's third law, Newton showed that for a pair of bodies, the
orbit size, A, orbital period T, and their combined masses M, are related to each other by
T squared is proportional to A cubed over M, and that those bodies orbit their common center
of mass, where one body is much more massive than the other, as is the case of an artificial
satellite orbiting a planet. It is a convenient approximation to take the center of mass as
coinciding with the center of the more massive body. Advances in Newtonian mechanics were then used
to explore variations from the simple assumptions behind Kepler orbits, such as the
perturbations due to other bodies, or the impact of spheroidal rather than spherical
bodies, Yosef Louis-Logrange developed a new approach to Newtonian mechanics,
emphasizing energy more than force, and made progress on the three-body problem,
discovering the Lagrangian points with Euler.
In a dramatic vindication of classical mechanics, in 1846, Urban Le Verre was able to predict
the position of Neptune, based on unexplained perturbations in the orbit of Uranus.
Albert Einstein in his 1916 paper, the foundation of the general theory of relativity,
explained that gravity was due to curvature of space-time
and remove Newton's assumption that changes in gravity propagate instantaneously.
This led astronomers to recognize that Newtonian mechanics did not provide the highest accuracy in understanding orbits.
In relativity theory, orbits follow geodesic trajectories,
which are usually approximated very well by the Newtonian predictions,
except where there are very strong gravity fields and very high speeds,
but the differences are measurable.
Essentially, all the experimental evidence that can distinguish between the theories agrees with relativity theory to within experimental measurement accuracy.
The original vindication of general relativity is that it was able to account for the remaining unexplained amount in procession of Mercury's perihelion, first noted by La Verrier.
However, Newton's solution is still used for most short-term purposes, since it is significantly easier to use and sufficiently accurate.
Within a planetary system, various non-stellar objects follow elliptical orbits around the system's barricentering center.
These objects include planets, dwarf planets, asteroids, and other minor planets.
planets, comets, meteoroids, and even space debris.
A comet in a parabolic or hyperbolic orbit about a barycenter
is not gravitationally bound to the star,
and therefore is not considered part of the star's planetary system.
Bodies that are gravitationally bound to one of the planets
in a planetary system, including natural satellites,
artificial satellites, and the objects within ring systems,
follow orbits about a berry center near or within that planet.
Owing to mutual gravitational perturbations,
the eccentricities and inclinations of the planetary orbits vary over time.
Mercury, the smallest planet in the solar system,
has the most eccentric orbit.
At the present epic, Mars has the next largest eccentricity, while the smallest orbital eccentricities are seen with Venus and Neptune.
As two objects orbit each other, the periapsis is that point at which the two objects are closest to each other.
Less properly, perifocus or pericentron are used.
The apoapsus is that point at which they are the farthest, or sometimes apophocus, or apocentron.
A line drawn from periapsis to apoapsis is the line of absities.
This is the major axis of the ellipse, the line through its longest part.
More specific terms are used for specific bodies.
For example, paragy and apogee are the lowest and highest parts of an orbit around Earth.
While perihelian and apelion are the closest and farthest points of an orbit around the sun,
things orbiting the moon have a periloon and apolloon, or parasolini and apocelini respectively.
An orbit around any star, not just the sun.
as a periastron and apastron.
In the case of planets orbiting a star,
the mass of the star and all its satellites
are calculated to be at a single point called the Bury Center.
The individual satellites of that star
follow their own elliptical orbits
with a Bury Center at one focal point of that ellipse.
At any point along its orbit,
any satellite will have a certain value
of kinetic and potential energy
with respect to the berry center.
And a sum of those two energies
is a constant value at every point along its orbit.
As a result, as a planet approaches periapsis,
the planet will increase in speed
as its potential energy decreases.
As a planet approaches apoapsis,
its velocity will decrease,
as its potential energy increases.
An orbit can be explained by combining Newton's laws of motion
with his law of universal gravitation.
The laws of motion are as follows.
A body continues in a state of uniform rest or motion
unless acted upon by an external force.
The acceleration produced when a force acts
is directly proportional to the force,
and takes place in the direction in which the force acts.
To every action, there is an equal and opposite reaction.
By the first law of motion in the absence of gravity,
a physical object will continue to move in a straight line due to inertia.
According to the second law, a force, such as gravity,
pulls the moving object toward the body that is the source of the force,
and thus causes the object to follow a curved trajectory.
If the object has enough tangential velocity,
it will not fall into the gravitational body,
but can instead continue to follow the curved trajectory caused by the force indefinitely.
The object is then said to be orbiting the body,
According to the third law, each body applies an equal force on the other, which means the two bodies orbit around their center of mass, or berry center.
Because of the law of universal gravitation, the strength of the gravitational force depends on the masses of the two bodies and their separation.
As the gravity varies over the course of the orbit, it reproduces Kepler's laws of planetary motion.
Depending on the evolving energy state of the system, the velocity relationship of two moving objects with mass can be considered in four practical classes with subtypes.
No orbit.
Suborbital trajectories.
A range of interrupted elliptical paths.
Orbital trajectories.
Orbally orbits.
Range of elliptical paths with closest point opposite firing point.
Circular path.
Range of elliptical paths with closest point at firing point.
Open or escape trajectory.
Parabolic Paths
Hyperbolic Paths
To achieve orbit, conventional rockets are launched vertically at first
To lift the rocket above the dense lower atmosphere
Which causes frictional drag
And gradually pitch over and finish firing the rocket engine parallel to the atmosphere
To achieve orbital injection
Once in orbit, their speed keeps them above the atmosphere.
If an elliptical orbit dips into dense air,
the object will lose speed and re-enter, following to the ground.
Occasionally, a spacecraft will intentionally intercept the atmosphere
and enact commonly referred to as an arrow-breaking maneuver.
As an illustration of an orbit around a planet,
the Newton's cannonball model may prove useful.
This is a thought experiment,
in which a cannon, on top of a tall mountain,
is able to fire a cannonball horizontally at any chosen muzzle speed.
The effects of air friction on the cannonball are ignored,
or perhaps the mountain is high enough that the cannon is above the earth's atmosphere,
which is the same thing.
If the cannon fires its ball with a low initial speed,
the trajectory of the ball curves downward and hits the ground.
As the firing speed is increased,
the cannon ball hits the ground farther away from the cannon.
Because while the ball is still falling towards the ground,
the ground increasingly curving away from it.
All these motions are actually orbits in a technical.
They are describing a portion of an elliptical path that run the center of gravity,
but the orbits are interrupted by striking the earth.
If the cannon ball is fired with sufficient speed,
the ground curves away from the ball at least as much as the ball falls,
so the ball never strikes the ground.
It is now in what could be called a non-interrupted or circummedent.
or circumnavigating orbit.
For any specific combination of hide above the center of gravity
and mass of the planet,
there is one specific firing speed,
unaffected by the mass of the ball,
which is assumed to be very small relative to the Earth's mass
that produces a circular orbit.
As the firing speed is increased beyond this,
non-interrupted elliptic orbits are produced.
If the initial firing is above the surface of the urs,
there will also be non-interrupted elliptical orbits at slower firing speed.
These will come closest to the urs at the point half an orbit beyond
and directly opposite the firing point below the circular orbit.
At a specific horizontal firing speed called escape velocity,
dependent on the mass of the planet
and the distance of the object from the berry center,
an open orbit is achieved that has a parabolic path.
At even greater speeds,
the object will follow a range of hyperbolic trajectories.
In a practical sense,
both of these trajectory types
mean the object is breaking free of the planet's gravity
and going off into space,
potentially never to return.
However, the object remains under the influence of the sun's gravity.
In most real-world situations,
Newton's laws provide a reasonably accurate description of motion of objects in a gravitational field.
The adjustments needed to accommodate the theory of relativity
become appreciable in cases where the object is in the proximity of a significant,
gravitational source, such as a star, or a high level of accuracy is needed.
The acceleration of a body is equal to the combination of the forces acting on it,
divided by its mass.
The gravitational force acting on a body is proportional to the product of the masses of the two attracting bodies
and decreases inversely with the square of the distance between them.
them. For a two-body problem, defined as an isolated system of two spherical bodies with known
masses and sufficient separation, this Newtonian approximation of their gravitational interaction
can provide a reasonably accurate calculation of their trajectories. If the heavier body is much
more massive than the smaller, as in the case of a satellite or small moon or, or a small moon
orbiting a planet, or for the Earth orbiting the Sun,
it is accurate enough and convenient
to describe the motion in terms of a coordinate system
that is centered on the heavier body.
And we say that the lighter body is in orbit around the heavier.
For the case where the masses of two bodies are comparable,
an exact Newtonian solution is still sufficient.
and can be had by placing the coordinate system at the center of the mass of the system.
Energy is associated with gravitational fields.
A stationary body far from another can do external work if it is pulled towards it
and therefore has gravitational potential energy.
Since work is required to separate two bodies against the pull of gravity,
their gravitational potential energy increases as they are separated
and decreases as they approach one another.
For point masses,
the gravitational energy decreases to zero
as they approach zero separation.
It is convenient and conventional
to assign the potential energy as having zero value
when they are an infinite distance apart.
And hence it has a negative value, since it decreases from zero or smaller finite distances.
When only two gravitational bodies interact, their orbits follow a conic section.
The orbit can be open, implying the object never returns, or closed, returning,
which it is depends on the total energy, kinetic plus potential energy of the system.
In the case of an open orbit, the speed at any position of the orbit is at least the escape velocity for that position.
In the case of a closed orbit, the speed is always less than the escape velocity, since the kinetic energy is never negative if the common convention is adopted of taking the potential energy as zero at infinite separation.
The bound orbits will have negative total energy.
The parabolic trajectories, zero total energy,
and hyperbolic orbits, positive total energy.
An orbit will have a parabolic shape if it has a velocity of exactly the escape velocity
of that point in its trajectory.
And it will have the shape of a hyperbola when its velocity is,
greater than the escape velocity. When two bodies approach each other with escape velocity
or greater relative to each other, they will briefly curve around each other at the time
of their closest approach, and then separate and fly apart. All closed orbits have the shape
of an ellipse. A circular orbit is a special case, where the foci of the ellipse coincide.
bodies following closed orbits repeat their paths with a certain time called the period.
This motion is described by the empirical laws of Kepler, which can be mathematically derived from Newton's laws.
These can be formulated as follows.
1. The orbit of a planet around the sun is an ellipse.
with the sun in one of the focal points of that ellipse.
This focal point is actually the bury center of the sun planet system.
For simplicity, this explanation assumes the sun's mass is infinitely larger than the planets.
The planet's orbit lies in a plane called the orbital plane.
2.
As the planet moves in its orbit, the line from the sun to the planet sweeps a constant.
an area of the orbital plane for a given period of time, regardless of which law of its orbit the planet
traces during that period of time. This means that the planet moves faster near its perihelian
than near its epahelion, because at the smaller distance, it needs to trace a greater arc to
cover the same area. This law is usually stated as equal areas in the same area. This law is usually stated as equal areas
in equal time.
3.
For a given orbit, the ratio of the cube of its semi-major axis to the square of its period is constant.
Ideally, the bound orbits of a point mass or a spherical body with a Newtonian gravitational
field form closed ellipses, which repeat the same path exactly and indefinitely.
However, any non-sherical or non-Newtonian effects will cause the orbit's shape to depart from the ellipse.
Such effects can be caused by a slight oblateness of the body, mass anomalies, tidal deformations, or relativistic effects,
thereby changing the gravitational field's behavior with distance.
The two-body solutions were published by Newton and Principia in 1687.
In 1912, Carl Fridiof Sunman developed a converging infinite series
that solves the general three-body orbit.
However, it converges too slowly to be of much use.
The restricted three-body problem in which the third body is assumed to have negligence,
mass has been extensively studied.
The solutions to this case include the Lagrangian points.
In the case of lunar theory,
the 19th century work of Charles Eugène Doolani
allowed the motions of the moon to be predicted
to within its own diameter over a 20-year period.
No universally valid method is known to solve the equations of motion
motion for a system with four or more bodies.
The following derivation applies to an elliptical orbit.
The assumption is that the central body is massive enough that it can be considered to be stationary,
and so the more subtle effects of general relativity can be ignored.
The Newtonian law of gravitation states that the gravitational acceleration of the second
mass towards the central body is related to the inverse of the square of the distance between them.
Namely, the force on object 2 equals negative G times m, 1 times m, 2 over R squared.
Where F sub 2 is the force acting on the mass M sub 2, caused by the gravitational attraction,
mass M sub 1 has for M sub 2.
G is a universal gravitational constant,
and R is the distance between the two masses centers.
From Newton's second law,
the summation of the forces acting on M sub 2
related to that body's acceleration,
the force on object 2 equals its mass times its accelerates,
times its acceleration, where A sub 2 is the acceleration of M sub 2, caused by the force of gravitational attraction F sub 2 of M sub 1 acting on M sub 2.
