# All Questions

60 questions
64 views

### Two-body problem - point of closest approach

I am reading through an exercise : One of the hints to solve this problem is that at the point of closest approach the comet's velocity must be tangential only, why is this the case ?
69 views

### Two black holes colliding (classical mechanics)

I had this question come up in my exam where two identical black holes are in orbit around each other. There is a loss of energy via gravitational waves : $$\frac{d E}{d t} = kr^4\omega^6$$ where $k$ ...
71 views

### Barycentre of two planets and calculating velocity shift

I find my self puzzled by this question, and I cant see anything wrong with my derivation, which leads me to believe that there is something I am missing within how the velocity shift is calculated. I ...
48 views

### Spirals in newtonian celestial mechanics?

I know Kepler's laws, Newton's laws, and that conic sections are the trajectories of noncolliding two point masses. But I wonder about a point mass A eventually colliding with point mass B. In ...
54 views

### Is the speed of an orbiting object at a given distance enough to uniquely classify an orbit's eccentricity?

As in the title, I am having trouble with part ii and iii of the linked image. So far i have found the semi-major axis and the period of the orbit both using the vis-viva equation along with proving ...
328 views

### Which Kepler laws might change with the Universal Gravitational Constant?

I was recently asked the following question: Which of the Kepler Laws change if the Universal Constant Of Gravitation is changed? And why? I list the 3 laws of Kepler below: The Law of Orbits: ...
255 views

### Speed at the perihelion [closed]

Hale Bopp has a period of 2400 days, with a mean distance from the sun at 174 AU and 1AU away in perihelion and 357 AU away in aphelion, what is its speed at the perihelion? what formulas do you need ...
50 views

### How can I obtain the position of the Earth on the orbit for given date?

I would like to be able calculate (or at least download some time-series data of) the position of the Earth on it's orbit at given date. For my purposes, it would be sufficient to account for the ...
604 views

### How to calculate a planet's tangential velocity moving in an elliptic orbit? [duplicate]

Consider a planet of mass $m$ moving around the Sun of mass $M$ in a circular orbit of radius $r$. By equating the centripetal force to $\frac{mv^2}{r}$ to gravitational attraction $\frac{GMm}{r^2}$, ...
250 views

### How are the Lagrange points determined?

According to Hyper Physics, there are 5 equilibrium, or Lagrange points of the Earth-Moon system and only 2 of them are said to represent stable equilibrium points. This made me think if there is an ...
330 views

### Third law of Kepler [closed]

I can not find any solution to this exercise on the internet. Calculate the mean radius of the orbit of a fictitious planet X, expressed in kilometers and UA, so that its orbital period is 1.9x10 ...
272 views

### How did people get ellipses of Newton's equations of motion and gravitation? [duplicate]

It has become somewhat general knowledge that from Newton's laws of motion and his law of universal gravitation it is possible to verify that the trajectories of the planets are ellipses, i remember ...
70 views

### What are the gravitational implications of a planet orbiting a star perpendicular to the star's axis of rotation?

I just read about the planet KELT-9b, and one thing which stuck out to me was the fact that this planet orbits this star parallel to the star's axis of rotation (the article says "perpendicular", but ...
88 views

### Problem: Spectroscopy of a binary system

The Problem is: For a binary system (2 Stars) with Orbital Period of $P =4.822 days = 416620.8 second$ and inclination $i=90$ and with speeds very less than $3 .10^8 m/s$. Their orbital planes around ...
197 views

98 views

### Angular momentum for planet is constant [closed]

In this excersie we look at the system of the dwarf star Gliese 536. Gliese 536 is 10 Parsec away and has half the mass of the sun. (I guess, they mean our sun). There are hints, that there a so ...
113 views

4k views

### What would become of the earth's orbit if half of the sun's mass were suddenly to disappear? [closed]

I shall assume that the sun is at rest, so before the half mass disappear, the orbit of earth is an ellipse.
782 views

### What is the distance between two objects in space as a function of time, considering only the force of gravity? [duplicate]

What is the distance between two objects in space as a function of time, considering only the force of gravity? To be specific, there are no other objects to be considered and the objects in question ...
247 views

### Units in gravitational N-body simulations

I use a code in Python to simulate a binary system interacting through gravity. You can find it here; The code works fine. I am however having problems with the units of length and velocity. I ...
437 views

### How do I calculate the effect of a prograde, retrograde, radial and anti-radial burn on the orbital elements of a two-dimensional orbit?

My relevant knowledge: This question works in two dimensions, with a two-body problem (see bottom for context). To my understanding, a two-dimensional orbit has the following orbital elements (3D ...
1k views