UFO Size Estimator

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Introduction

GO TO ESTIMATOR

(Best viewed at 1024 x 768 resolution or higher)

Estimating the size of a UFO can be a tricky thing. This method of estimation requires fairly accurate determinations of the angular size of a UFO, and its distance from the observer, compared to the apparent size of a known object such as the Moon.

MEAN LUNAR DIAMETER/DISTANCE CONSTANT ( Cd )
Cd is the ratio of the Moon's diameter divided by its mean distance from the Earth.

There are a few methods for determining the angular width of a UFO but the one used here is based on comparisons with the angular size of the moon and a constant value derived from the Moon's actual diameter (2160 miles) divided by the Moon's mean distance from the Earth (238856 miles).
Cd = diameter / Distance = 2160mi / 238856mi = 0.009043105.

RELATIVE MEAN LUNAR DIAMETER ( Rm )
Rm is the ratio of the UFO's angular size to the Moon's angular size.

The first item to determine is the angular width of the UFO. How big is it compared to the moon? Is it twice the diameter? Half of the diameter? a tenth? Use the Angular UFO Size Chart below and find the silhouette closest to UFO size compared to the moon images.

UFO DISTANCE ( Dobj )

Distance is from the observer to the UFO. Distance can be determined a few different ways. One method is to estimate the angle of elevation of the UFO then measure the distance to the point on the ground directly below the UFO. You can then divide that distance by the cosine of the angle to arrive at the actual distance.

If Dg = the ground distance and Ae = the angle of elevation then the actual distance is

Dobj = Dg / cos( Ae )

us_fig1.jpg (19385 bytes)

UFO LENGTH ( Lufo )

Using the values from above one can estimate the length of the UFO with the formula

Lufo = Cd Dobj Rm

Using the distance example above (1103 ft.) let's say the UFO appeared to be twice the diameter of the angular moon then

Lufo=	Cd	x	Dobj	x	Rm
Lufo =	0.00904	x	1103 ft.	x	2
Lufo =	19.96 ft.

This UFO would be about 20 ft. wide

How to use the calculator

Shape of UFO:   Select the shape closest to that of the UFO. The shape of the image is not used in the calculation but rather it is there to give you an approximate visual of the UFO compared to that of the moon. Selecting a different shape will not effect results.

Ground Distance to UFO: Dg   Type in the ground distance to the object. This is the distance from your observing point to the point on the ground directly below the UFO. You can enter values in feet (1st box) or meters (2nd box). Each will recalculate the other. for instance if you enter 500 in the feet box, 152.4 will appear in the meters box. If you type 500 in the meters box, 1640.4199 will appear in the feet box.

Angle of Elevation to UFO: Ae   Type in the angle of elevation of the UFO in degrees. If you aren't sure you can approximate the angle by counting the number of closed vertical fists above the horizon to the object. One fist is about 10° so an object that is 3 1/2 fists above the horizon is about 35°.

Mean Lunar Width of UFO: Rm   Adjust image size: Type in an estimated value in Mean Lunar widths. If the object was 3/4ths the size of the full moon then type in .75. If it was twice the size type in 2 etc.
or,
Select a size increment button '' (Mean Lunar widths) then use the buttons to increase/decrease the image size by the selected value. You can speed up resizing by selecting a button and then pressing or holding down the <Enter> key on your keyboard.
The image display only goes to 22 Mean Lunar widths but you may type in any Mean Lunar Width value you wish

Results update each time a parameter is changed. If this doesn't happen with your browser then use the button to update the results. The button resets all values to their defaults. The default UFO size is two Mean Lunar widths.

Shape

OvalSphereTriangle
CylinderBulletCigar

Enter Ground Distance Dg	Feet	Meters
Enter Ground Distance Dg

Enter Angle of Elevation Ae	degrees

	Feet	Meters
Distance
Altitude

Est. Length of UFO
Feet	Meters

Mean Lunar Width of UFO Rm

	1/32	1/16	1/8	1/4	1/2	1

The image display only goes to 22 lunar widths but you may type in any Lunar Width value you wish

Glossary

Angular Size The size that an object appears to be. If you held a ruler up to a car that was 100 yards away it would appear to be only inches long.
Angle of elevation Ae - The angle in degrees from the horizon to the UFO
Ground Distance Dg - The distance from the observer to the point on the ground directly below the UFO.
Relative Mean Lunar Size Rm - The UFO's size in angular Mean Lunar widths. This is a subjective value based on how big the moon appears to be in the sky. A good guide is to hold an aspirin tablet out at arms length. This will be roughly the same angular size as the full moon.