<p>With an albedo of 0.09 (<a href="https://ui.adsabs.harvard.edu/abs/2017arXiv170302670M/abstract" rel="nofollow noreferrer">Mallama 2017</a>), it's true that Mercury has the lowest albedo of all planets. But reflecting 9% of something that is really, really, really bright, is still pretty bright.</p>
<p><em>Comment from Darth Pseudonym</em>: For comparison, the Moon's albedo is 0.12 on average, so Mercury reflects almost as much as the Moon.</p>
<p>Being close to the Sun <em>is</em> a problem. Mercury is brightest when almost behind the Sun so that it is &quot;full&quot; and we see the full reflecting face of the planet. Moreover, the albedo is actually larger in this configuration, because planets tend to reflect light preferentially back in the direction of the illuminating source. However, in this case it would be daytime, as seen from Earth, so that the Sun outshines Mercury (at least to the naked eye; you <em>can</em> in fact see it in a telescope, but be careful not to catch the Sun).</p>
<p>Therefore Mercury is best observed roughly at &quot;half-Mercury&quot;, at which point according to <a href="https://en.wikipedia.org/wiki/Mercury_(planet)#Observation" rel="nofollow noreferrer">Wikipedia</a> its separation from the Sun is roughly 18° to 28°. This puts Mercury well into the twilight and even night, although you do need a rather unobstructed view toward the horizon, as its altitude will be correspondingly low.</p>
<p>Based on the phase, distance, and albedo you can then calculate the apparent brightness (e.g. by following the steps in <a href="https://astronomy.stackexchange.com/a/5983/5264">this answer</a>), and you'll find that Mercury's magnitude alternates between roughly 6 (barely visible) and –2 (brighter than Sirius; the brightest star on the sky). Even in twilight, seeing the brightest stars is no problem, unless you're in the middle of a large city.</p>
<p>Here's a diagram (generated from <a href="https://theskylive.com/how-bright-is-mercury" rel="nofollow noreferrer">this site</a>) showing how the apparent magnitude changes throughout the coming year:</p>
<p><a href="https://i.sstatic.net/s5LVf.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/s5LVf.png" alt="mMerc" /></a></p>
<p><em>Comment from PM2Ring</em>: You can compare this to Mercury's separation from the Sun to see when it is best observed. Here's a plot of their ecliptic longitude and latitude for the next three months, where numbers are given for every 7 days:</p>
<p><a href="https://i.sstatic.net/qY7jn.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/qY7jn.png" alt="enter image description here" /></a>
<sup>Credit: User <a href="https://astronomy.stackexchange.com/users/16685/pm-2ring">@PM2Ring</a>.</sup></p>

CC BY-SA 4.0
2024-01-02T16:18:11.720Z
It's worth noting that the moon's albedo is 0.12 on average (it varies wildly because moondust has a retroreflective property) so Mercury isn't THAT much darker than a half-moon...
Darth Pseudonym
CC BY-SA 4.0
2024-01-02T17:53:34.207Z
Here's a plot of the ecliptic longitude & latitude of Mercury & the Sun, for 2024-Jan-1 to 2024-Apr-1, with numeric labels every 7 days. https://i.sstatic.net/6JyJ7.png
PM 2Ring
CC BY-SA 4.0
2024-01-02T20:44:21.057Z
@DarthPseudonym Yes, good point!
pela
CC BY-SA 4.0
2024-01-02T20:49:57.677Z
@PM2Ring Thanks, that's also very informative!
pela
CC BY-SA 4.0
2024-01-05T09:26:38.367Z
@PM2Ring I stole your plot and put in into my answer :) I hope you don't mind (but let me know if you'd rather want to use it in a separate answer).
pela
CC BY-SA 4.0
2024-01-05T09:28:42.827Z
@pela You're more than welcome to use my plot!
PM 2Ring
CC BY-SA 4.0
2024-01-02T14:36:46.577Z
2024-01-05T09:23:01.773Z
2024-01-05T09:23:01.773Z
pela
<p>How is it possible that Mercury can be seem from Earth if it is such a small planet, it has the lowest albedo of any planet, and it is so close to the Sun?</p>

CC BY-SA 4.0
2024-01-02T14:22:14.117Z
And is also brightly lit...
Jon Custer
CC BY-SA 4.0
2024-01-02T17:36:28.210Z
There are periods where you can see Mercury clearly. See: https://astronomy.stackexchange.com/a/46954/35206
Nilay Ghosh
<mercury>
Why is Mercury visible
Stephen
# Why is Mercury visible

(Asked by: username_0 on 2024-01-02)

How is it possible that Mercury can be seem from Earth if it is such a small planet, it has the lowest albedo of any planet, and it is so close to the Sun?

**Tags:** mercury

> **Comments:**
> **username_1**: And is also brightly lit...  
> **username_2**: There are periods where you can see Mercury clearly. See: https://astronomy.stackexchange.com/a/46954/35206  

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## 1 answers

### Answer by username_3 on 2024-01-02. Score: 7

With an albedo of 0.09 ([Mallama 2017](https://ui.adsabs.harvard.edu/abs/2017arXiv170302670M/abstract)), it's true that Mercury has the lowest albedo of all planets. But reflecting 9% of something that is really, really, really bright, is still pretty bright.

*Comment from username_4 username_4*: For comparison, the Moon's albedo is 0.12 on average, so Mercury reflects almost as much as the Moon.

Being close to the Sun *is* a problem. Mercury is brightest when almost behind the Sun so that it is "full" and we see the full reflecting face of the planet. Moreover, the albedo is actually larger in this configuration, because planets tend to reflect light preferentially back in the direction of the illuminating source. However, in this case it would be daytime, as seen from Earth, so that the Sun outshines Mercury (at least to the naked eye; you *can* in fact see it in a telescope, but be careful not to catch the Sun).

Therefore Mercury is best observed roughly at "half-Mercury", at which point according to [Wikipedia](https://en.wikipedia.org/wiki/Mercury_(planet)#Observation) its separation from the Sun is roughly 18° to 28°. This puts Mercury well into the twilight and even night, although you do need a rather unobstructed view toward the horizon, as its altitude will be correspondingly low.

Based on the phase, distance, and albedo you can then calculate the apparent brightness (e.g. by following the steps in [this answer](https://astronomy.stackexchange.com/a/5983/5264)), and you'll find that Mercury's magnitude alternates between roughly 6 (barely visible) and –2 (brighter than Sirius; the brightest star on the sky). Even in twilight, seeing the brightest stars is no problem, unless you're in the middle of a large city.

Here's a diagram (generated from [this site](https://theskylive.com/how-bright-is-mercury)) showing how the apparent magnitude changes throughout the coming year:

[![mMerc](https://i.sstatic.net/s5LVf.png)](https://i.sstatic.net/s5LVf.png)

*Comment from username_5*: You can compare this to Mercury's separation from the Sun to see when it is best observed. Here's a plot of their ecliptic longitude and latitude for the next three months, where numbers are given for every 7 days:

[![enter image description here](https://i.sstatic.net/qY7jn.png)](https://i.sstatic.net/qY7jn.png)
Credit: User [@username_5](https://astronomy.stackexchange.com/users/16685/username_5).

> **Comments:**
> **username_4**: It's worth noting that the moon's albedo is 0.12 on average (it varies wildly because moondust has a retroreflective property) so Mercury isn't THAT much darker than a half-moon...  
> **username_5**: Here's a plot of the ecliptic longitude & latitude of Mercury & the Sun, for 2024-Jan-1 to 2024-Apr-1, with numeric labels every 7 days. https://i.sstatic.net/6JyJ7.png  
> **username_3**: @username_4 Yes, good point!  
> **username_3**: @username_5 Thanks, that's also very informative!  
> **username_3**: @username_5 I stole your plot and put in into my answer :) I hope you don't mind (but let me know if you'd rather want to use it in a separate answer).  
> **username_5**: @username_3 You're more than welcome to use my plot!  

---

