Why not the sun revolves around the Earth?

Click For Summary

Discussion Overview

The discussion revolves around the question of why the Earth is considered to revolve around the Sun rather than the other way around. Participants explore the implications of different reference frames in analyzing planetary motion, touching on concepts from classical mechanics and the historical context of astronomical models.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question the validity of analyzing planetary motion from the Earth's frame, suggesting that the center of mass frame is closer to an inertial frame, which simplifies calculations.
  • Others argue that both "The Earth orbits the Sun" and "The Sun orbits the Earth" can be considered true from different reference frames, highlighting the psychological impact of human perception of motion.
  • A participant notes that the center of mass of the Earth-Sun system is very close to the Sun due to its larger mass, allowing for an approximation that simplifies the analysis of their motion.
  • Some contributions emphasize that in a vacuum, the motion of massive and lighter objects can appear differently depending on the chosen frame of reference.
  • There is a mention of the historical Ptolemaic model being incorrect, but the discussion does not reach a consensus on the implications of this for current understanding.
  • A later reply suggests that considering the center of mass of the Earth and Sun may not be useful due to the significant mass difference, indicating that the Sun's mass can be treated as dominant in calculations.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the analysis of planetary motion from different reference frames. There is no consensus on the implications of these perspectives or the best approach to understanding the motion of the Earth and Sun.

Contextual Notes

Some limitations include the dependence on definitions of reference frames, the unresolved nature of certain mathematical steps, and the implications of historical models on current understanding.

hackhard
Messages
183
Reaction score
15
why was Earth considered to revolve around the sun and nt the other way round?
why is it wrong to analyze planetary motion from Earth frame?
 
Astronomy news on Phys.org
hackhard said:
why is it wrong to analyze planetary motion from Earth frame?
It's not wrong, but the system's center of mass frame is closer to an inertial frame, making the math simpler.
 
I can't find it now but I remember reading somewhere about someone lamenting the supposed poor education of our kids by claiming that such-and-such percentage of kids couldn't "correctly" answer whether the Sun orbits the Earth, or the Earth orbits the Sun. However, of course, the statement "The Earth orbits the Sun" and "The Sun orbits the Earth" are equally true! They are each true in different reference frames. Of course the center of mass of the Earth-Sun system is very close to the center of the Sun. Also, it's a known fact that the Ptolemaic model is definitely not true. However, the real problem is that the public implicitly assumes that there is a universal frame of reference. Humans evolved on the surface of the Earth, where the ground you are walking on is an always present obvious frame of reference, so that shapes our psychology.
 
A.T. said:
the system's center of mass frame is closer to an inertial frame, making the math simpler.
can you please explain how ?
 
hackhard said:
can you please explain how ?
Look up inertial and non-inertial frames of reference.
 
so analyzing motion from sun frame saves from worying about pseudo forces
 
hackhard said:
can you please explain how ?
Let me explain how. As David Neves explained sun and Earth is in fact revolving around their common center of mass and to analyze this motion you also need to consider the position of the center of mass and position of sun and earth. However since the sun is much more massive than earth, the center of mass of this system is inside the sun. So we can say that the Earth is revolving around the sun(not center of sun but very close to it). So even though the center of mass is not inertial we can approximate it because in that way we can take position of center of mass constant and this makes life easier because we don't deal with a function of time anymore but a constant.
 
Note that the center-mass frame is not precisely the rest frame of the sun, although it's very close, because the mass of the sun is much larger than the mass of the earth, but more precise is to say that both the Earth and the sun orbit around their common center of mass. The reason is that in this frame the two-body problem reduces to an effective one-body problem, namely that of a mass ##\mu=m_1 m_2/(m_1+m_2)## orbiting around the origin in a gravitational potential $$V(r)=-\Gamma m_1 m_2/r=-\Gamma \mu (m_1+m_2)/r.$$
 
  • Like
Likes   Reactions: davenn
hackhard said:
why was Earth considered to revolve around the sun and nt the other way round?
why is it wrong to analyze planetary motion from Earth frame?
If only that they can find a fixed reference in the universe, then we may able say what is moving around what. With respect to that reference, chances are the sun might be revolving around the Earth or may be the earth. What are your thoughts on this?

Is it not right that massive objects revolves around the lighter ones in a vacuum? What are the odds?
 
Last edited:
  • #10
Ronie Bayron said:
Is it not right that massive objects revolves around the lighter ones in a vacuum?
depends on choice of frame
isolated particles can appear to revolve and revolving particles can appear to purely translate when viewed from certain non-inertial frames
 
  • #11
hackhard said:
depends on choice of frame
isolated particles can appear to revolve and revolving particles can appear to purely translate when viewed from certain non-inertial frames
I think Galileo was half right for that fact--(not unless rebutted by someone)
Anyhow, I admired your semi-cyborg goggles:smile:. Is it functional? Just asking.
 
  • #12
There are other planets orbiting the Sun, and the Earth is so small, so it's not very useful to consider the center of mass of the Earth and Sun. The Sun is so much more massive that you might as well neglect the mass of the Earth.
 

Similar threads

High School How Does a Massive Planet's Orbit Around the Sun Appear?
  • · Replies 6 ·
Replies
6
Views
2K
High School The Sun's Influence on the Moon's Orbit: Is it Negligible?
  • · Replies 4 ·
Replies
4
Views
3K
High School Question about the Sun's gravitational influence on the Earth and its moon
  • · Replies 8 ·
Replies
8
Views
2K
Undergrad Earth-centered frame with Earth-Sun line fixed
  • · Replies 3 ·
Replies
3
Views
1K
High School Evolution of planetary system around a white dwarf
  • · Replies 0 ·
Replies
0
Views
2K
High School What is the shape of an asteroid impact on Earth?
  • · Replies 3 ·
Replies
3
Views
2K
High School What reference frame is used for the velocity v in the Lorentz transformation?
  • · Replies 53 ·
2
Replies
53
Views
2K
High School Process of a sun changing into a white dwarf
  • · Replies 5 ·
Replies
5
Views
2K
High School How long it takes the Earth to fall halfway to the Sun--ellipse method
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad About the relation between number of sidereal and solar days
  • · Replies 27 ·
Replies
27
Views
4K