Exposing PseudoAstronomy

August 13, 2010

Why You Can’t Believe ANYONE Who Says They Know the Size and Distance of a UFO


Hi all, sorry that I haven’t been writing for a few weeks, I’ve been really busy with work, with a revised impetus to finish my Ph.D. ASAP since I have a possible offer of a post-doc.

Anyway, the topic for today is UFOs. UFOs are actually a subject that I have specifically avoided on this blog for the most part because they encompass a huge set of phenomena, from abductions, to sightings, to anal probing, to alien-human hybrids, to reptilians under the Denver airport and more. Yeah, a lot of stuff.

This particular post will be very focused on a single subject: Why you can’t believe any report that states a UFO’s size, distance, and speed. And also, for the purpose of this post, if it wasn’t already obvious, UFO is a place-holder for what people think are IFOs … identified flying objects as alien craft. An “actual” UFO is just that – an unidentified flying object, not an, “I saw a UFO that was a craft with 3 lights on it and it was 100 meters long!” That’s an identification.

Size, Distance, and Speed

These are three characteristics of a moving object that are often used in UFO reports, either any two of them, or all three. For example, a UFO report witness may state, “I saw a craft that was 3 miles across, maybe 1000 feet up but moving very slowly, unlike any aircraft we have.”

Such a report, however, has no basis in reality.

There, I said it. Quite dismissive, isn’t it? However, once you understand the basic idea, you’ll see why any report or witness that claims any two or all three of these qualities is either simply na├»ve or just making it up.

We’ll Start with Speed

When a police officer measures your speed, they do so when you are usually several tens or hundreds of feet away, either with a laser or radar or something similar. When they’re doing this, you must be moving either towards (usually, so they can get behind you and catch you) or away from the police officer. And not just in that general direction, but almost directly towards or away.

Why? No, it’s not just because roads are generally straight, it’s because if you are moving at a diagonal, the police officer will only get a measurement of the velocity towards or away from them. Your velocity across their line of sight cannot be measured by their device.

Similarly, that is the first problem with a UFO report that claims a speed. Let’s for the moment say the object actually is a flying craft. Even so, The observer will only be able to estimate the speed across their line of sight, so effectively left-right and/or up-down. Any motion towards or away from them cannot be measured accurately because it would rely upon the trigonometry of calculating the change in size of the object due to perspective.

As I said, that’s the first problem with speed. The second problem with it is the crux of this issue and why size and distance are impossible to report.


Anything you see in your vision covers a certain angle. Let’s take a computer monitor, since if you’re reading this chances are you are familiar with a computer monitor. As you read this sentence, if your face is fairly close to the monitor, then the letters are relatively large, covering a large angle across your vision. Now if you move your head away from the screen, then the letters cover a smaller angle of your vision, and hence appear smaller.

You have an innate sense of how far away the screen is from your head. Chances are that you can extend your arm and touch the screen. It’s probably between 1 and 4 feet from you (0.3-1 meter). Because you know how far it is from you, you also can estimate its size. You also have context to estimate its size. It’s probably sitting on a desk, or if you’re on a laptop then maybe on a couch, desk, your lap, or unfortunately an airplane tray table. Years of experience have taught you how large the objects around you are, and you can place the computer screen within that context to estimate its size.

Let’s extend this to a different place, the produce section of your local grocery. You grab a small pepper, let’s say a serrano. You hold the serrano pepper up to your face, and it appears rather large. You look at the far wall over to the heads of iceberg lettuce. Relative to the lettuce, the pepper looks much larger — it covers a larger angle of your vision. But you know that serrano peppers are smaller than heads of iceberg lettuce. You have context, and you have every day experience, and you know how far away these objects are from you because you have easy things you can measure by.

Take it to the Sky

In the sky, things are different. Very different. You have no context. You cannot reach out your hand and measure how far away something is. You don’t know how large objects are because you cannot take a measuring stick there and use it. If a fly were buzzing two inches (5 cm) from your face, it would look bigger than an airplane flying at 30,000 ft (9 km). Similarly, a bird flying 100 ft up (30 m) will look gigantic relative to the international space station.

This is why you cannot measure the size nor distance of a UFO. Its size depends upon its distance, and its distance depends upon its size. And, its speed depends upon its distance (a kid on a tricycle just outside your house will appear to move faster than a car on a highway 10 miles (15 km) away).

If you don’t know how far away the UFO is, which you don’t because you have no way to measure it, then you cannot know how large it is physically. You are solely relying on the apparent angular size. Similarly, if you don’t know how big it is, which you can’t know because you have no context, then you have no way to estimate how far away it is.

Final Thoughts

Once you understand this concept, it is very, very easy to understand why skeptics will dismiss all reports of this kind of information (size, distance, and speed). It is also easy to understand why skeptics are unimpressed when an eyewitness — be they a hillbilly farmer, a metropolitan police chief, or an astronaut — state that a UFO they saw was 3 miles across, or a kilometer across and zipping through the sky faster than any known aircraft.

It’s, quite simply, not possible to know, unless you can physically measure at least either the actual distance to the object or its physical – not angular – size.

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