<p>You just need to add the 13.4  that you got to the 6 that you can see without a telescope and that's it.  The formula is telling you the difference in magnitude that arises from the different apertures of the eye and the telescope.</p>

CC BY-SA 4.0
2018-11-30T20:37:36.413Z
And that's because it's m - M = to that. I just had to make sure because the answer thingy that I got isn't particularly the best and has many mistakes in it
Math Love
CC BY-SA 4.0
2018-11-30T13:48:29.610Z
2018-11-30T13:48:29.610Z
Dr Chuck
<p>All I know is its main mirror diameter; 2.40 m</p>

<p>I also know that the eye, which its pupil is 5mm in diameter can see up to an apparent magnitude of 6.</p>

<p>How can I calculate the apparent magnitude that the telescope can see?</p>

<p>I have used the equation of </p>

<p><span class="math-container">$5⋅log(\frac{D_1}{D_0})$</span>
However, it gave the answer of 13.40, while the answer should be 19.40</p>

CC BY-SA 4.0
2018-11-30T13:12:07.570Z
No, it's not. First of all, this is GROUND telescope, NOT a space one. Secondly, this doesn't have a transmission factor.
Math Love
CC BY-SA 4.0
2018-11-30T13:20:02.067Z
What do you know about the magnitude scale, and what have you tried so far?
Dr Chuck
CC BY-SA 4.0
2018-11-30T13:24:40.530Z
the other question starts with the Hubble but the answer directs us to the general formula in wikipedia, also talking about the background contrast, so it definitely applies to the ground observations
szulat
CC BY-SA 4.0
2018-11-30T13:33:23.037Z
It gives the wrong answer, the answer should be +19.4 mag while the one I got is 13.4. There's 6 magnitudes difference, that's why I asked
Math Love
CC BY-SA 4.0
2018-12-01T00:05:02.937Z
The question as it's currently written asks "How can I calculate the apparent magnitude that the telescope can see?", and the other question provides the answer, so I'm voting that this is a duplicate. **However**, if you reword your question to ask "I'm using this formula for my [details] telescope but I get +13.4 instead of +19.4 - where is my error?" it would be a different question and not a duplicate. And it would directly address the issue you're having :-)
Chappo Hasn't Forgotten
<astrophysics>
What is the apparent magnitude of the weakest stars we can see in one telescope on the ground with a diameter of 2.4m?
Math Love
# What is the apparent magnitude of the weakest stars we can see in one telescope on the ground with a diameter of 2.4m?

(Asked by: username_0 on 2018-11-30)

All I know is its main mirror diameter; 2.40 m

I also know that the eye, which its pupil is 5mm in diameter can see up to an apparent magnitude of 6.

How can I calculate the apparent magnitude that the telescope can see?

I have used the equation of

$5⋅log(\frac{D\_1}{D\_0})$
However, it gave the answer of 13.40, while the answer should be 19.40

**Tags:** astrophysics

> **Comments:**
> **username_0**: No, it's not. First of all, this is GROUND telescope, NOT a space one. Secondly, this doesn't have a transmission factor.  
> **username_1**: What do you know about the magnitude scale, and what have you tried so far?  
> **username_2**: the other question starts with the Hubble but the answer directs us to the general formula in wikipedia, also talking about the background contrast, so it definitely applies to the ground observations  
> **username_0**: It gives the wrong answer, the answer should be +19.4 mag while the one I got is 13.4. There's 6 magnitudes difference, that's why I asked  
> **username_3**: The question as it's currently written asks "How can I calculate the apparent magnitude that the telescope can see?", and the other question provides the answer, so I'm voting that this is a duplicate. **However**, if you reword your question to ask "I'm using this formula for my [details] telescope but I get +13.4 instead of +19.4 - where is my error?" it would be a different question and not a duplicate. And it would directly address the issue you're having :-)  

---

## 1 answers

### Answer by username_1 on 2018-11-30. Score: 4 | Accepted answer

You just need to add the 13.4 that you got to the 6 that you can see without a telescope and that's it. The formula is telling you the difference in magnitude that arises from the different apertures of the eye and the telescope.

> **Comments:**
> **username_0**: And that's because it's m - M = to that. I just had to make sure because the answer thingy that I got isn't particularly the best and has many mistakes in it  

---

