Why Don’t We See Any Satellites In The Pictures of Earth?

We are often contacted by our readers with questions whose answers seem incredibly obvious. Posts like “Where does sugar go after being dissolved?“, “What is the ISS?” or “Where do fish come from in newly formed ponds?” are just some of the many articles that were attempts to answer such questions.

A few days ago, a reader wanted to know the answer to yet another seemingly basic, but very interesting question – why don’t we see any satellites in the numerous pictures of Earth taken from a great distance? If you’re not clear what we’re talking about, go ahead and look up ‘pictures of Earth’ on the Internet. To make it even more convenient for you, I’ll just put a collage of some pictures of Earth right here:

Do you see any satellites in any of them?

If you really think about it, it’s actually quite a valid question. I mean, there are a few thousand satellites orbiting the Earth, and these are just the man-made ones. If you consider every object orbiting our planet, the number would be much higher. There are about 21,000 objects (larger than 10 centimeters) and about 500,000 or so smaller pieces of orbital debris spinning around the Earth right now .

Why don’t we see any of that in our numerous pictures of Earth?

Short answer: The Earth is too big and these objects are too small in comparison to be visible in the same photograph. 

First, let’s briefly take a look at the number of ‘space objects’ circling our planet.

Objects orbiting the Earth

There are thousands upon thousands of objects spinning around the Earth. Some of them are very small (i.e. less than 10 centimeters across) while others are quite huge, relatively speaking.

Man-made objects

Let’s briefly talk about the numerous man-made objects around the planet. Take the ISS, for example.

Image Source: Nasa.gov

It’s approximately 109 meters (356 feet) by 73 meters (240 feet). To put in perspective, it’s slightly larger than a football field. This is the largest (and also, the costliest) man-made object currently orbiting the planet. Apart from that, there are thousands of man-made objects, including the Hubble Space Telescope, Astrosat, NOAA 18 and many other Earth-observation satellites constantly spinning around the Earth.

Space debris

A photo of space debris around Earth released by NASA (Image Credit: Wikimedia Commons)

Note that these are only the currently operational ones; there are a number of defunct satellites up there too that cannot be repaired. They’re basically going to have to stay up there until they gradually lose altitude and burn up in the atmosphere. These types of satellites add up to a huge amount of space junk, which is a big cause of concern for future space flights.

Natural objects

Apart from man-made satellites and space junk, there are also tens of thousands of celestial objects circling the planet. Such objects have sizes ranging from a couple centimeters to a few feet.

Paths of potentially hazardous asteroids near Earth

There’s one singular takeaway from all of this – there are a LOT of objects circling our planet.

Why are satellites and celestial objects not visible in pictures of Earth?

The answer is pretty straightforward – it’s because Earth is very, very big. It’s hard to say why, but people generally tend to underestimate the sheer enormity of our planet. Our planet is HUGE, in the real sense of the word. In comparison, the objects that orbit the planet are – for the lack of a better word to denote minuteness – puny.

Take the ISS – the biggest man-made object currently spinning around the planet – for example. It has a surface area of around 2,500 square meters or 0.0025 square km, which is almost equal to the size of a 6-bedroom apartment. In contrast, the surface area of the Earth is 510.1 million km squared. We can now calculate how many ISS’es would it need to completely cover the Earth’s surface by applying simple arithmetic.

So, it would take 204 billion ISS’es to entirely cover the planet! To have some idea of what this means visually, take a look at this picture:

A comparison between the size of Earth and the ISS (the biggest man-made satellite in space). (Note: The distance between these two is not to scale).

Note that the pictures of Earth do have satellites in them; however, they’re too tiny to be resolved in the image. Most images of our planet are only a few thousand pixels in diameter; so unless an object is of the order of a kilometer or more (which no object in the vicinity of the planet is), it would only be a fraction of a pixel, and thus invisible in the image. Furthermore, many satellites and a great deal of space debris are above the altitude of the ISS (which clicks a lot of pictures of our planet), so it’s not going to capture an enormous number of objects in the picture anyway, since they’re not there in the first place!

However, there are occasions when you can see a satellite in an Earth-picture, but it would be too small (yes, “magnifying glasses-small”), and practically indistinguishable from the stars in the backdrop.

So, if someone asks why they can’t see satellites in the images of Earth, ask them why a picture of their house doesn’t show the two dozen flies nearby, or why a full-body picture doesn’t show the huge number of bacteria and germs living on their body. Hopefully, that will help them understand!

Why Is Wet Paper So Weak And Easy To Tear?

Gather a bunch of used papers, pile them up and try to tear the stack in half. If you’re not an unusually powerful fellow, it’s highly unlikely that you could tear it. Now, put that same stack in a bucket full of water and let it soak for a while. Take it out a few minutes later and try to tear it again. You should be able to tear it very easily… why is that?

Why does paper become so incredibly weak when it’s wet?

Short answer: Paper is composed of fibers that are tangled together; they start to separate from each other when water is introduced.

What is paper made of?

You must have heard many times that we should conserve paper because “trees are cut down to make them”. Well, that’s exactly right. In essence, a piece of paper is just wood.

Wood is actually a heterogeneous substance; 40-50% of it is micro-fibrils of cellulose and 15-25%  is hemicellulose, both of which are held together by a natural glue called ‘lignin’.  To make paper out of wood, you first need to turn raw wood into ‘pulp’ – a watery soup of cellulose fibers, water, lignin and certain other chemicals used during the process. After the pulp is ready, it goes through several additional processes to ultimately take the form of paper as we know it.

Cellulose structure

You might have read or heard the term ‘cellulose’ many times in discussions pertaining to cotton, wood, dried hemp and other similar materials. It is the most abundant organic polymer (an organic substance whose molecular structure consists of a large number of similar units bonded together) on the planet. It is the chemical structure of cellulose, which happens to be the most important constituent of paper, that keeps the paper ‘rigid’ when dry and extremely fragile when wet.

Take a look at the structural formula of cellulose:

Cellulose consists of many hydroxyl groups (-OH).

The numerous hydroxyl groups (-OH) present in cellulose form hydrogen bonds with oxygen atoms on the same chain or a neighboring chain. Also, one thing you should know about hydrogen bonds – they are incredibly strong! They help hold the long chains of cellulose together and impart that ‘sturdiness’ to paper.

What happens when paper gets wet?

Introducing water to paper brings about a drastic change in its ability to ‘stand up straight’, which severely comprises its strength. You see, cellulose is hydrophilic , meaning that it has an affinity towards water and tends to dissolve in it. When water is added to paper, the hydrogen bonds holding the cellulose fibers begin to break down. This is because water molecules consist of oxygen and hydrogen atoms, which form hydrogen bonds with cellulose fibers, thus weakening their own hydrogen bonds in the process.

In short, you could say that adding water leads to the weakening of the fiber-fiber bonds of paper and leads to an unsteady equilibrium of fiber-fiber and fiber-water.

Wetting paper has a dramatic influence on the strength of paper, such that you could easily tear huge stacks of them apart with little effort. In fact, paper becomes so weak that it can disintegrate all by itself, which can be pretty bad in some cases.

We all know that wet paper is incredibly weak, so it should be handled with the utmost care. Still, now that you are equipped with a bit of scientific insight into how the disintegration of wet paper actually works, perhaps you’ll check your pockets twice before doing the laundry