<p>The key to answering your question is to know the albedo of the asteroid compared to the Moon. The Moon is rather dark (reflecting 7% to 12% of the light if I remember correctly, about as black as worn asphalt). I think, but do not know with certainty, that the asteroid would not be much darker.</p>

<p>For the dimensions that you give, the asteroid would be approximately the same apparent size as the moon: 0.45 x 0.65° compared to the Moon's 0.5°.</p>

<p>So both have approximately the same albedo and approximately the same size. Therefore I say that the asteroid would be visible in the daylight.</p>

<p>Also this is a sci-fi story, correct? If you can get the asteroid into that orbit, then anything is possible. :-)</p>

CC BY-SA 3.0
2017-07-25T14:44:38.923Z
It would be roughly the size of the moon? I didn't think of calculating its apparent size. Comes as a surprise to me. (: I read somewhere where M class asteroids are relatively bright compared to the average planetoid.
catsteevens
CC BY-SA 3.0
2017-07-26T14:50:25.050Z
Using the example [here](https://en.wikipedia.org/wiki/Absolute_magnitude#Apparent_magnitude_2), I figure the asteroid has a "full asteroid" magnitude of about -12. So you are correct!
catsteevens
CC BY-SA 3.0
2017-08-07T15:48:00.797Z
So at times there are 2 moons of roughly the same size in our sky. Awesome, as the kids say.
catsteevens
CC BY-SA 3.0
2017-07-25T02:30:20.093Z
2017-07-25T02:30:20.093Z
JohnHoltz
<p>In a story I'm working on, a huge, 20 by 14 kilometer, Ni-Fe asteroid attains a 1760 km. orbit around earth (why/how? Long story). I figure it has an H magnitude of ~12. Would this body be visible naked-eye from the surface during the day?</p>

CC BY-SA 3.0
2017-07-25T08:58:47.280Z
If it has a H magnitude of 12, then no. Nowhere near. However, such a large object would have a much brighter H magnitude than12 at that distance.
ProfRob
CC BY-SA 3.0
2017-07-31T19:56:46.450Z
[H](https://en.wikipedia.org/wiki/Absolute_magnitude#Example) is the apparent magnitude at 1 A.U.
catsteevens
CC BY-SA 3.0
2017-07-31T20:20:15.803Z
1au from what? The H magnitude you quote bears no relation to the other physical quantities in your question.
ProfRob
CC BY-SA 3.0
2017-08-01T14:27:23.410Z
??? The observer, of course.
catsteevens
CC BY-SA 3.0
2017-08-01T15:00:56.323Z
The apparent brightness of an asteroid depends on the distance from the Sun and the distance from the observer and the Sun-asteroid-observer angle. In any case, the apparent infrared magnitude (however defined) is not especially relevant to its naked-eye visibility.
ProfRob
<asteroids><apparent-magnitude>
Asteroid visible during the day?
catsteevens
# Asteroid visible during the day?

(Asked by: username_0 on 2017-07-24)

In a story I'm working on, a huge, 20 by 14 kilometer, Ni-Fe asteroid attains a 1760 km. orbit around earth (why/how? Long story). I figure it has an H magnitude of ~12. Would this body be visible naked-eye from the surface during the day?

**Tags:** asteroids, apparent-magnitude

> **Comments:**
> **username_1**: If it has a H magnitude of 12, then no. Nowhere near. However, such a large object would have a much brighter H magnitude than12 at that distance.  
> **username_0**: [H](https://en.wikipedia.org/wiki/Absolute_magnitude#Example) is the apparent magnitude at 1 A.U.  
> **username_1**: 1au from what? The H magnitude you quote bears no relation to the other physical quantities in your question.  
> **username_0**: ??? The observer, of course.  
> **username_1**: The apparent brightness of an asteroid depends on the distance from the Sun and the distance from the observer and the Sun-asteroid-observer angle. In any case, the apparent infrared magnitude (however defined) is not especially relevant to its naked-eye visibility.  

---

## 1 answers

### Answer by username_2 on 2017-07-25. Score: 5 | Accepted answer

The key to answering your question is to know the albedo of the asteroid compared to the Moon. The Moon is rather dark (reflecting 7% to 12% of the light if I remember correctly, about as black as worn asphalt). I think, but do not know with certainty, that the asteroid would not be much darker.

For the dimensions that you give, the asteroid would be approximately the same apparent size as the moon: 0.45 x 0.65° compared to the Moon's 0.5°.

So both have approximately the same albedo and approximately the same size. Therefore I say that the asteroid would be visible in the daylight.

Also this is a sci-fi story, correct? If you can get the asteroid into that orbit, then anything is possible. :-)

> **Comments:**
> **username_0**: It would be roughly the size of the moon? I didn't think of calculating its apparent size. Comes as a surprise to me. (: I read somewhere where M class asteroids are relatively bright compared to the average planetoid.  
> **username_0**: Using the example [here](https://en.wikipedia.org/wiki/Absolute_magnitude#Apparent_magnitude_2), I figure the asteroid has a "full asteroid" magnitude of about -12. So you are correct!  
> **username_0**: So at times there are 2 moons of roughly the same size in our sky. Awesome, as the kids say.  

---

