I know that viewing Mercury is a challenge, but I'm fairly close to the equator and Mercury was at greatest elongation just a week ago.

In-the-sky.org says:

All around the world, Mercury is visible as an evening object, having recently passed greatest elongation east. From Taipei, however, it is not observable – it will reach its highest point in the sky during daytime and is no higher than 10° above the horizon at dusk.

12 Jul 2018, 12:00 CST – Mercury at greatest elongation east 27 Aug 2018, 05:48 CST – Mercury at greatest elongation west 06 Nov 2018, 22:59 CST – Mercury at greatest elongation east 15 Dec 2018, 23:17 CST – Mercury at greatest elongation west

Of course, since Mercury stays near the Sun it will always reach its highest point in the sky during daytime, probably around lunchtime!

But I don't understand why it would be viewable all around the world (presumably just after sunset since it is currently near maximum elongation East), but not from Taipei.

Question: Why does in-the-sky.org say that Mercury is not visible from Taipei these days?

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1 Answer 1


The logic that In-The-Sky.org uses to decide whether events are observable or not doesn't currently work very well for Mercury and Venus. I have some plans to fix this in the long term, but always have far too many projects on the go.

As you correctly say, it's blazingly obvious that Mercury is highest in the sky at lunchtime, and the code I wrote to generate these descriptions should realise that (but doesn't, currently).

The statement that Mercury is going to be very challenging to observe from Taipei is basically correct. At this time of year, Mercury doesn't venture very far from the Sun, even at greatest elongation. The best time to see it in the evening sky is around late September. This is true regardless of where you live in the world, so the statement "all around the world..." in the web page is basically wrong.

As I say, I have plans to improve all of this, but the website is a one-man effort, done entirely in my spare time, so things don't always get fixed quickly :-)

  • 1
    $\begingroup$ It's a fantastic site, I love it, and use it all the time! You can see a screen shot and a home-made GIF as well here Thanks for your amazingly speedy reply! $\endgroup$
    – uhoh
    Jul 19, 2018 at 16:19

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