Why does Venus always appear close to the Sun in the sky?

In summary, Venus is considered the "Morning Star" or the "Evening Star" because it can only be seen near sunrise and sunset, as it is always close to the Sun in the sky. This is due to Venus being an inner planet, along with Mercury, and their orbits being smaller than Earth's, resulting in them always appearing close to the Sun from an observer on Earth. In contrast, outer planets such as Jupiter and Saturn can be seen anywhere in the sky, as their orbits are larger than Earth's and they can appear at various distances from the Sun.
  • #1
Riccardo K
1. The problem statement, all variables, and given/known data

Venus is sometimes described as either the “Morning Star” or the “Evening Star”, since it can only be seen near sunrise and sunset, very close to the Sun in the sky. Why does Venus always appear close to the Sun in the sky for an observer on the Earth, and which other planet would you expect to be the same?

Homework Equations


None

The Attempt at a Solution


For the first part of the question what I understood was the Venus never more than 48° to the Sun, but at the same time major planets like Jupiter, Saturn and more are on the other part of the Sun. The other planet would be Mercury as Venus and Mercury as the inner planets of our Solar System, but due to it being very close to the sun and very small, I suppose it is easy to lose track of it in the Sun's Glare. Another thing I discovered was that Copernicus said that Mercury and Venus orbit the Sun with orbits smaller than Earth’s. The problem for me is that I can't piece all of this information together to find an answer to the First Part of the Question. The Second Part I am sure is Mercury.

Thanks for any help provided.
 
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  • #2
This can be visualised geometrically.

Take the two bits you mentioned, or rather the one bit you mentioned twice:
Riccardo K said:
Venus and Mercury as the inner planets of our Solar System
Riccardo K said:
Mercury and Venus orbit the Sun with orbits smaller than Earth’s
and start drawing.

Draw the Sun and Earth in its orbit (doesn't have to be to scale - just points and circles). Then draw another planet with the largest possible orbit that is still inside Earth's. Connect the three (Sun, Earth, and the planet) to form a triangle.

The angle at the vertex marked with Earth's position shows the separation of the Sun and the planet on the sky.
What is the largest possible value of this angle? How does it change if you make the orbit of the planet even smaller?

Next, draw a planet on a larger orbit than Earth's and do the same thing. What is the largest value of the same angle now?
 
  • #3
Sorry, but I do not understand. I drew the Sun as a Big circle then did a circle that is meant to represent the orbit line and drew a small circle on that line to represent Earth, and then I drew a Line which was really close to the orbit line of Earth but still in between Earth and the Sun and added a small circle on that line. Then I connected the Sun, Earth, and Planet together to form a Triangle. Not sure what to do next
 
  • #4
Riccardo K said:
Not sure what to do next
Look at the angle in the triangle at the vertex where Earth is. How large can you make this angle by moving the other planet around on its orbit? Can you, for example, make it 90 degrees? 180?
 
  • #5
I should have drawn it with a rule now that I think about it, I don't have one with me right now, but Ill figure something out
 
  • #6
Is the extra planet Venus, as it would go clock wise instead of all the other planets?
 
  • #7
Riccardo K said:
Is the extra planet Venus, as it would go clock wise instead of all the other planets?
It doesn't matter. It can be imaginary. Call it Steve or something. You're just trying to show what maximum angle on the sky between the Sun and an inner planet can be.
(maybe use MS Paint, or Google Draw and show your work here)

And Venus is not orbiting clockwise. It's rotating clockwise.
 
  • #9
Great.
Do you think it's possible to make the angle at Earth's vertex 180 degrees? 90? 60? 45? If yes, where would the other planet have to be in those cases?
 
  • #10
  • #11
It's all good. Try to answer the question above.
 
  • #12
If you make the vertex over 90 degrees you can no longer see that planet and the question is stating that we can always see it so I think you can not have it at 180. I know that Venus does not go over 48° so the planet should be around here> http://prntscr.com/g1rs1y
 
  • #13
Yes, very good. In fact, if you made the orbit of the other planet almost exactly like the orbit of the Earth, you could make that angle 60 degrees at maximum.

Now, if you were to think of a planet on a higher orbit, are there any such restrictions? Can you make the angle between the Sun and an outer planet 90 degrees? 180?
 
  • #14
  • #15
What is the angle between the sun and the outer planet in the picture below? (Earth is the inner planet)
upload_2017-7-29_13-30-38.png
 
  • #16
180 Degrees
 
  • #17
Right. So can you now make an argument why some planets can be seen anywhere in the sky, while others are confined to being next to the Sun?
 
  • #18
Would it be because Venus always appears close to the sun in the sky due to it being on the opposite side of the Sun and Earth Being in the middle and Mercury can only be seen as long as it does not a certain angle go over the sun?
 
  • #19
I'm sorry. I'm having a hard time understanding your response.

But maybe let me lead you a bit more - M & V are inner planets, as you yourself have stated, right? This is actually the straight answer to the problem question. But you need to be able to substantiate it with some argument.

So what is it that you have then shown about how far away (in terms of angular separation on the sky) from the Sun they can be seen, and how that differs from outer planets?
 
  • #20
Ok
Inner Planets have to be less than 90 degrees for them to be seen from Earth, but Outer Planets can be over 90 degrees but still less than 180 to be seen from Earth
 
  • #21
Just checked. Apparently just saying that M and V are inner planets should do. Thanks for all the help given. I think I understood a bit more now.
 
  • #22
Riccardo K said:
Sorry, but I do not understand. I drew the Sun as a Big circle then did a circle that is meant to represent the orbit line and drew a small circle on that line to represent Earth, and then I drew a Line which was really close to the orbit line of Earth but still in between Earth and the Sun and added a small circle on that line. Then I connected the Sun, Earth, and Planet together to form a Triangle. Not sure what to do next
What do you mean that you drew the sun as a big circle ? Represent the Sun and all other planets with dots. Represent the orbits with circles. The circle representing the orbit of Venus is smaller than that of the Earth, and the orbit of Mars and the outer planets like Jupiter are bigger than that of the Earth. On the figure, the blue dot is Venus, the brawn one is Earth, the red one is Mars, and the black one might be Jupiter (not in scale).At position A, Venus looks farthest from the Sun, and it looks closer at positions B and C.
upload_2017-7-29_14-15-18.png
 
Last edited:
  • #23
I don't really get it
 
  • #24
I understand that the rules of this section of the forums say, that if I don't arrive at the answer then you are not allowed to tell me. Thanks for all the help given, but I don't think I will understand this further not having studied Astronomy at school yet.
 

What causes Venus to always appear close to the Sun in the sky?

Venus orbits closer to the Sun than Earth, so it always appears relatively close to the Sun in the sky. Additionally, Venus's orbit is tilted compared to Earth's, meaning it can appear above or below the Sun in the sky depending on its position in its orbit.

Is Venus always visible when it appears close to the Sun in the sky?

No, Venus is only visible when it is above the horizon and not obscured by clouds or atmospheric conditions. It can be difficult to spot Venus when it is close to the Sun in the sky, especially during the day.

Why does Venus sometimes appear brighter than other times when it is close to the Sun in the sky?

Venus's brightness in the sky is due to its highly reflective atmosphere, which can vary in thickness and cloud cover. When there are more clouds, Venus appears brighter, and when there are fewer clouds, it appears dimmer.

Can Venus ever appear farther away from the Sun in the sky?

Yes, Venus can appear farther away from the Sun in the sky when it is on the opposite side of its orbit from Earth. This is known as its "greatest elongation" and can occur up to 47 degrees away from the Sun.

How does Venus's orbit affect its position in the sky?

Venus's orbit is elliptical, meaning its distance from the Sun can vary. This affects its position in the sky, as it can appear closer or farther from the Sun depending on where it is in its orbit. Additionally, Venus's orbit is tilted compared to Earth's, which also affects its position in the sky relative to the Sun.

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