<p>As Mercury is inclined by 7 degrees relative to the orbit of the Earth (the ecliptic) at any given time it may be above the ecliptic or below. However there are two times during its orbit when it crosses the ecliptic. These are known as "nodes". </p>

<p>A conjunction occurs when the planet is vertically above or below the sun. A superior conjunction happens when the planet is on the far side of the sun, an inferior conjunction happens when the planet is closer to the Earth than the sun.</p>

<p>When a node occurs at about the same time as an inferior conjunction, then the planet will appear to travel in front of the sun. Whether it travels through the middle of the solar disk, or through the upper or lower part, depends on whether the exact time of the node occurs just before the conjunction or just after. </p>

<p>In May 2016, Mercury crossed the ecliptic at about 08:00 (utc), and had it inferior conjuction at about 15:00. It was a little below the ecliptic by the time of conjunction, but still close enough to cross the solar disk.</p>

<p>The exact position of Mercury also depends on the location you are viewing from on Earth, a fact that Edmond Halley noticed could be exploited to calculate the distance to the planet, and by extension, the distance to the sun.</p>

CC BY-SA 3.0
2016-05-11T19:42:08.270Z
2016-05-11T19:42:08.270Z
James K
<p>Why did Mercury not appear to transit through the middle of the sun (the equator)? I initially thought that this was because of the ecliptic, but, then I thought that actually we'd see it above the solar equator, wouldn't we? So I'm confused. </p>

<p>This <a href="https://www.youtube.com/watch?v=AhWMOkrzKzs" rel="nofollow">video of the transit</a> from NASA shows exactly what I'm talking about. Mercury is shown relatively low on the solar disk.</p>

<p>I'm looking specifically for why it was visible in the bottom half of the sun, not the top half?</p>

CC BY-SA 3.0
2016-05-11T07:24:31.313Z
Because, Earth, Mercury and the sun were not all in a perfect line. (If Earth and Mercury's orbits were not inclined - i.e. were in a perfect flat plane - we would see several transits per year in fact.)
Andy
CC BY-SA 3.0
2016-05-13T21:53:29.207Z
Why did you think "that actually we'd see it above the solar equator, wouldn't we" ? Did you not wonder why this is not seen every Mercury year? Most Mercury years, it does not pass in front of the Sun at all (for some good reason explained in the answers), so when it does, why should it go through the equator?
Walter
<solar-system><planetary-transits><ecliptic>
Why did Mercury not appear to transit through the middle of the sun?
Software Engineer
# Why did Mercury not appear to transit through the middle of the sun?

(Asked by: username_0 on 2016-05-10)

Why did Mercury not appear to transit through the middle of the sun (the equator)? I initially thought that this was because of the ecliptic, but, then I thought that actually we'd see it above the solar equator, wouldn't we? So I'm confused.

This [video of the transit](https://www.youtube.com/watch?v=AhWMOkrzKzs) from NASA shows exactly what I'm talking about. Mercury is shown relatively low on the solar disk.

I'm looking specifically for why it was visible in the bottom half of the sun, not the top half?

**Tags:** solar-system, planetary-transits, ecliptic
> **Comments:**
> **username_1**: Because, Earth, Mercury and the sun were not all in a perfect line. (If Earth and Mercury's orbits were not inclined - i.e. were in a perfect flat plane - we would see several transits per year in fact.)  
> **username_2**: Why did you think "that actually we'd see it above the solar equator, wouldn't we" ? Did you not wonder why this is not seen every Mercury year? Most Mercury years, it does not pass in front of the Sun at all (for some good reason explained in the answers), so when it does, why should it go through the equator?  

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## 1 answers

### Answer by username_3 on 2016-05-11. Score: 1

As Mercury is inclined by 7 degrees relative to the orbit of the Earth (the ecliptic) at any given time it may be above the ecliptic or below. However there are two times during its orbit when it crosses the ecliptic. These are known as "nodes".

A conjunction occurs when the planet is vertically above or below the sun. A superior conjunction happens when the planet is on the far side of the sun, an inferior conjunction happens when the planet is closer to the Earth than the sun.

When a node occurs at about the same time as an inferior conjunction, then the planet will appear to travel in front of the sun. Whether it travels through the middle of the solar disk, or through the upper or lower part, depends on whether the exact time of the node occurs just before the conjunction or just after.

In May 2016, Mercury crossed the ecliptic at about 08:00 (utc), and had it inferior conjuction at about 15:00. It was a little below the ecliptic by the time of conjunction, but still close enough to cross the solar disk.

The exact position of Mercury also depends on the location you are viewing from on Earth, a fact that Edmond Halley noticed could be exploited to calculate the distance to the planet, and by extension, the distance to the sun.


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