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On the 11th November 2019, Mercury will transit the Sun from our viewpoint on Earth.
This won’t be noticeable to the naked eye, but with the right equipment, you’ll be
able to see the silhouette of Mercury against the Sun.
I’m Alex McColgan, and you’re watching Astrum, and in this video I’ll go through
the what, when and where of this transit, and also explain why this doesn’t happen
a lot more regularly.
A transit is where a celestial object passes in front of another object from our perspective,
but the perspective makes the closest body too small to eclipse the furthest one.
So, while the moon eclipses the Sun, only Mercury and Venus are positioned in such a
way that they can transit the Sun.
This is because they are the only planets that orbit closer to the Sun than we do.
When Earth and either Mercury or Venus align between us and the Sun, this is called an
inferior conjunction.
Now, the closer to the Sun a planet is, the shorter its year.
That means for Mercury, one year lasts just 89 Earth days.
That means it whizzes around to Sun a few times in the time it takes the Earth to orbit
the Sun once.
If that is the case, why doesn’t a Mercury transit happen a few times a year?
This is because planets in our solar system, while all orbiting roughly on the solar system’s
plane, don’t all have perfectly flat and circular orbits.
Their orbital eccentricity isn’t huge, but it’s enough when you take into account the
vast distances between these relatively small objects.
So, for most orbits, Mercury is either too high or too low from our perspective to be
directly in front of the Sun.
However, every so often, the alignment is just right for a transit to happen.
Unlike with Venus, which has a very set length of time between transits, 2 eight years apart
and then a long gap of 121 and 105 years.
Sadly, if you wanted to see a Venus transit but haven’t already, you’ve probably missed
it for good, the next one being one hundred years away now.
Mercury on the other hand has a weird pattern, although there are usually about 13 transits
per century.
Very interestingly though, every transit of Mercury only happens in either May or November.
If this is something you would be interested to see, I wouldn’t miss the one this year,
or you’ll have a 13-years wait on your hands.
These videos you are seeing now were taken by the Solar Dynamics Observatory, a NASA
space telescope that is constantly monitoring the Sun, of the last transit that happened
in 2016.
So how can you view this transit yourself?
The first port of call I would suggest is to see if you have any local astronomy clubs
nearby.
They are usually keen to observe phenomena like these, and are generally happy for the
public to come along to such occasions.
If that’s not for you, you can use a telescope to observe it, however, be very aware that
you must use a sun filter, or you will definitely blind yourself.
You’ll have to see if your telescope has a Sun filter attachment you can use, I wouldn’t
necessarily recommend using a homemade one just in case it’s not made correctly, and
you still damage your eyes.
You can use the same glasses you used to look at a solar eclipse, although you’ll have
to have pretty good eyesight to see Mercury as it is so small.
My last suggestion would be to build your own, optical projection camera.
A simple pinhole camera won’t work in this instance, as again, Mercury is too small.
All you need are two pieces of thick card and binoculars.
Keep the binoculars steady and cut holes into one of the sheets so you can fit it around
the lenses seamlessly.
This is to block sunlight from all but the lens.
Block one of the lenses, you don’t need two projections.
Using the second sheet, hold it about 30cm away from the viewfinder and you should get
a projection of the sun.
Adjust the position of the sheet and the focus on the binoculars until you get a nice sharp
image.
With any luck, you’ll be able to see Mercury’s silhouette!
Again though, don’t look through the binoculars at the Sun yourself, just look at the projected
image for your eyes’ sake.
So, 11th November 2019.
What time can I see it?
Well that depends on where you are in the world.
It will begin at 12:35 UTC for Europe, Africa and the Middle East.
As the day progresses, it will start to become visible in the Americas.
Sorry Russia, Asia and Australasia, you’re out of luck.
If you happen to be at the South Pole, you’ll have a good view from start until finish.
So, there you have it, Mercury’s upcoming 2019 transit.
I hope you get to enjoy it and appreciate some of the more unusual sights of our solar
system!
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