How do I solve for the angle, as a function?

Click For Summary

Homework Help Overview

The discussion revolves around deriving a formula to express the angle at which Mars is observed from Earth, involving vector representations of their positions and the use of parametric equations. The subject area includes vector operations and trigonometry within the context of celestial mechanics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants explore expressing the angle in terms of the vectors for Mars and Earth, questioning how to account for the time-dependent nature of these vectors. There are attempts to apply the dot product and relate it to the angle, while some express uncertainty about how to visualize the problem and the specific angle to be derived.

Discussion Status

Participants are actively engaging with the problem, raising questions about the mathematical relationships involved and the necessary visualizations. Some guidance has been offered regarding the use of diagrams to clarify the relationships between the celestial bodies, but there remains a lack of consensus on the specific angle to be calculated.

Contextual Notes

There is mention of the challenge posed by the time-dependent nature of the vectors and the need to relate parametric equations to a more standard form for graphing. Participants are also navigating the constraints of the homework prompt, which specifies deriving a formula for the angle with respect to a defined axis.

Phantoful
Messages
30
Reaction score
3

Homework Statement


ATTACH]
EIFxygQ.png


Homework Equations


[/B]
The two equations in the image, as well as (maybe) standard vector operations like dot product, cross product.

The Attempt at a Solution


[/B]
So, I've tried to do what my instructor suggested and put everything in terms of Earth (Using RE and TE, but I'm not sure what to do from there as it doesn't seem that I'm progressing towards the solution. I've also tried to graph these functions, but I can't wrap my head around the fact that both the x and y vectors also have parameter t (time), so I'm not sure if graphing is the way to solve it. The main goal I've tried was to solve for theta, which doesn't seem possible because of the equations for x and y being split...
 

Attachments

  • EIFxygQ.png
    EIFxygQ.png
    23.6 KB · Views: 264
Physics news on Phys.org
Can you express the desired angle in terms of the two vectors, ##\vec R_M, \vec R_E##? I.e., as a vector equation?
 
haruspex said:
Can you express the desired angle in terms of the two vectors, ##\vec R_M, \vec R_E##?
I would think I'd need to do the dot product using |A|*|B|cosθ and then calculate theta, but would it even be possible to find the magnitude? The vectors are changing over time and I don't know how to account for that.

Edit: Sorry, re-read your question. Would I have to convert these 'parametric equations' to an x-y equation, and then graph?
 
Phantoful said:
the dot product using |A|*|B|cosθ
Dot product, yes, but not using that formula to find it. How do you perform a dot product on two vectors that are expressed in the same orthonormal basis?
 
haruspex said:
Dot product, yes, but not using that formula to find it. How do you perform a dot product on two vectors that are expressed in the same orthonormal basis?
I can also add after multiplying the x's and the y's, but that would be a scalar, is that what I want? So I'm adding cos(2π(t/TM))*cos(2π(t/TE))+sin(2π(t/TM))*sin(2π(t/TE)), or is it the (u⋅v/v⋅v)v equation?
 
Phantoful said:
I can also add after multiplying the x's and the y's, but that would be a scalar, is that what I want? So I'm adding cos(2π(t/TM))*cos(2π(t/TE))+sin(2π(t/TM))*sin(2π(t/TE)), or is it the (u⋅v/v⋅v)v equation?
Sorry, I think I've led you off in the wrong direction. Let's start again.

Draw a diagram of the Sun, Earth and Mars at some instant in the coordinate system given. Say we label the points S, E, M, and the distant star that fixes the X axis call P.
You can easily relate 2π(t/TE) and 2π(t/TM) to angles in the diagram, right?
What angle are you asked to find?
 
haruspex said:
Sorry, I think I've led you off in the wrong direction. Let's start again.

Draw a diagram of the Sun, Earth and Mars at some instant in the coordinate system given. Say we label the points S, E, M, and the distant star that fixes the X axis call P.
You can easily relate 2π(t/TE) and 2π(t/TM) to angles in the diagram, right?
What angle are you asked to find?
I'm not actually sure of 'what' angle I need to find, which is my big problem, because I can't visualize this well so I'm depending on the mathematics. The question says "Derive a formula for which we see Mars from Earth. This should be an angle with respect to the
Inline5.gif
-axis." I can't easily relate the equations to the diagram, because I don't have a clue what these should look like.
 

Attachments

  • Inline5.gif
    Inline5.gif
    289 bytes · Views: 817
This question will be the end of me...
 
Phantoful said:
I'm not actually sure of 'what' angle I need to find, which is my big problem, because I can't visualize this well so I'm depending on the mathematics. The question says "Derive a formula for which we see Mars from Earth. This should be an angle with respect to the View attachment 219525-axis." I can't easily relate the equations to the diagram, because I don't have a clue what these should look like.
Did you draw the diagram as I described?
What we are after is the angle that the line from Earth to Mars makes to the x axis.
We have vector representations for the positions of Earth and Mars. What vector represents the position of Mars relative to Earth?
 

Similar threads

Replies
26
Views
4K
Replies
8
Views
1K
Replies
8
Views
2K
Replies
5
Views
3K
  • · Replies 39 ·
2
Replies
39
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 16 ·
Replies
16
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K