Mercury is the first planet from the Sun, and one of the closest planets to us on Earth. This is especially true if you compare it to the ice giants Uranus and Neptune, which are much further out from the Sun. However, even though Mercury is relatively close to us, it can still be very difficult for us on Earth to see.
And actually, out of the five planets that we can see with the naked eye) Mercury, Venus, Mars, Jupiter and Saturn), Mercury is often touted as the most difficult to spot of the bunch. And when we consider that the distance between us and Mars is around double that of the distance between us and Mercury, it shows that distance isn’t the only factor at play here (Saturn is around 7 times the distance from us than Mercury is too).
But why is this, and what is it about Mercury that makes it tough for us to spot it? Well, there are a few different reasons why Mercury is difficult for us to see in the night sky, and we’re going to run through the main ones.
Why is Mercury difficult for us to see?
The key reason why Mercury is so difficult for us to see from Earth is that it is often in the same line of sight as the Sun. The Sun is so bright that when we do have the opportunity to see the planet, most of the time the glare from it make it impossible to get a clear view of Mercury.
Think about it – all of the planets that orbit the Sun pass round it at a different speed, so there are only certain times of year that they’ll be visible. Mercury makes one full orbit of the Sun in 88 days, so if we fit that into our yearly orbit of the Sun, there are a few times of year where we should have the opportunity to see it.
However, because we’re looking inwards to Mercury – is what is often dubbed as an inferior planet, as it’s closer to the Sun than us – it is often in the same line of sight as the Sun, So even though the Sun may not be directly behind it at all times, it is usually there to impair our view of the planet. This is just one of many important facts about Mercury.
Also worth considering is that although Mercury isn’t the hottest planet to orbit the Sun, it is the closest to it by some distance. It is only approximately 36 million miles (46 million km) away from the Sun, which means that it does orbit the Sun pretty tightly and doesn’t really give us much of an opportunity to see it.
This also means that when we can get a glimpse of Mercury, it is going to be very low on the horizon because of its proximity to the Sun. This makes a difference because that is where the atmosphere is thickest, meaning that it’s very difficult to see through.
Now, if we add into this that the orbital pattern of Mercury is the most elliptical of all the planets, then this rounds out the trifecta of reasons why it’s a tough cookie to spot. It doesn’t go around the Sun in a typical circle shape, much more an oval, meaning that it orbits the Sun at a close distance much of the time.
How can I see Mercury, then?
So, now we know why Mercury is so difficult for us to spot in the Night Sky, but that doesn’t really give us any tips on how to see it. The truth is that it definitely changes each year, and there will only be certain times you can spot Mercury in the night time.
Your best bet to spot Mercury in the night sky is to use a tool like Time and Date. This will give you the ability to know exactly when you’ll have the chance to see the planet and how clear the skies are, which will change from month to month and year to year.
All in all, there’s a good reason why astronomers have often touted Mercury as the most difficult to see of the viewable planets. This is in main because of Mercury’s positioning in relation to the Sun, but we can add in the Earth’s atmosphere as being another reason why it is very difficult to spot. For those brand new to astronomy, it’s usually easier to go for Venus first, because it’s so close to us on Earth.