<p>I was recently reading about the parallax effect and hence had a doubt about the parallax angle.
A lot of places mention the parallax angle as <code>(θ1 + θ2)/2</code> while in some places it is just mentioned as <code>(θ1 + θ2)</code>.</p>
<p><strong>NOTE: Here θ1 and θ2 are the two angles between the two points of observation and some reference point like a extremely distant star.</strong></p>
<p>Now, I wanted to know that which of the above mentioned formulas is correct for the parallax angle and <em><strong>what is reason behind its correctness</strong></em>. I also want to ask that what does the parallax angle actually represent/tell? Is it simply just the angle between the line of sights to a particular object like a star when viewed from two points or something else?</p>
<p>Also, when we use the parallax angle to calculate the distance to the star using parallax angle as <code>(θ1 + θ2)/2</code>then the distance to the star comes from <em>the sun to the star</em> <strong>{by using trigonometry}</strong> and when we calculate using the parallax angle as <code>(θ1 + θ2)</code> then the distance to the star comes from <em>the earth to the star</em> <strong>{by using the formula: D = b/θ}</strong>. So now which one of these is giving the correct distance?</p>

CC BY-SA 4.0
2023-05-02T13:19:03.957Z
You might want to add a source for those formulas, I can't imagine what they're trying to represent.  I would recommend looking up information on *parsec*, as that is generally the unit used to represent parallax.
Greg Miller
CC BY-SA 4.0
2023-05-02T16:15:10.520Z
What are $\theta_1$ and $\theta_2$?
ProfRob
CC BY-SA 4.0
2023-05-02T16:58:31.807Z
Here θ1 and θ2 are the two angles between the two points of observation and some reference point like a extremely distant star. It is also mentioned in the question itself.
Bhavya Jain
CC BY-SA 4.0
2023-05-02T17:06:31.050Z
A sketch might go a long way... when defining angles. And maybe then the answer also already becomes apparent. https://en.wikipedia.org/wiki/Parsec might give hints how to illustrate or explain the angles. I suspect it *might* read $(\theta_1 - \theta_2)/2$ if the measurments are with respect to the same object exactly half a year apart and angles measured with a sign.
planetmaker
<observational-astronomy><star><parallax>
What is the correct way to represent the Parallax angle?
Bhavya Jain
# What is the correct way to represent the Parallax angle?

(Asked by: username_0 on 2023-05-02)

I was recently reading about the parallax effect and hence had a doubt about the parallax angle.
A lot of places mention the parallax angle as `(θ1 + θ2)/2` while in some places it is just mentioned as `(θ1 + θ2)`.

**NOTE: Here θ1 and θ2 are the two angles between the two points of observation and some reference point like a extremely distant star.**

Now, I wanted to know that which of the above mentioned formulas is correct for the parallax angle and ***what is reason behind its correctness***. I also want to ask that what does the parallax angle actually represent/tell? Is it simply just the angle between the line of sights to a particular object like a star when viewed from two points or something else?

Also, when we use the parallax angle to calculate the distance to the star using parallax angle as `(θ1 + θ2)/2`then the distance to the star comes from *the sun to the star* **{by using trigonometry}** and when we calculate using the parallax angle as `(θ1 + θ2)` then the distance to the star comes from *the earth to the star* **{by using the formula: D = b/θ}**. So now which one of these is giving the correct distance?

**Tags:** observational-astronomy, star, parallax

> **Comments:**
> **username_1**: You might want to add a source for those formulas, I can't imagine what they're trying to represent.  I would recommend looking up information on *parsec*, as that is generally the unit used to represent parallax.  
> **username_2**: What are $\theta_1$ and $\theta_2$?  
> **username_0**: Here θ1 and θ2 are the two angles between the two points of observation and some reference point like a extremely distant star. It is also mentioned in the question itself.  
> **username_3**: A sketch might go a long way... when defining angles. And maybe then the answer also already becomes apparent. https://en.wikipedia.org/wiki/Parsec might give hints how to illustrate or explain the angles. I suspect it *might* read $(\theta_1 - \theta_2)/2$ if the measurments are with respect to the same object exactly half a year apart and angles measured with a sign.  

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## 0 answers

