Earth seen from the Moon will appear 3.7× larger than the Moon seen from Earth. However, if a photograph of Earth is compared to that of the Moon, the sizes of both objects also depend on the field of view of the cameras that were used to capture them.
Flat-Earthers discovered the size of the Earth in a photograph is not 3.7× the Moon in another picture. They used the fact as “evidence” of wrongdoing. In reality, the two photos were not taken with the same field of view, and cannot be compared directly.
The Apollo astronauts, who went to the Moon, used cameras equipped with a wide-angle lens most of the time. In some of their photos, they captured Earth. Because the cameras had a wide field of view, Earth appears very small in the frame.
On the other hand, if we want to take a photograph of the Moon, we often use a narrow field of view. The angular size of the Moon is only about 0.52°. Therefore, if we want to make the Moon as the primary object in our photograph, naturally, we have to use a narrow field of view. With zoom lenses, we will usually zoom all the way in, unless we want to include other objects in our composition.
The size of Earth in a photograph taken from the Moon and the size of the Moon in a photo taken from Earth cannot be directly compared unless we ensure both pictures were taken using the same field of view.
Apollo 17 Picture Analysis
- Sensor size: 70mm × 70mm, cropped by a reseau plate, leaving 54mm × 54mm effective exposure area.
- Lens: 60mm
- Field of view: 48° × 48°
- Horizontal angular diameter of the Earth from the image: 169px / 4086px * 48° = 1.99°
- Angular diameter of the Earth from Stellarium: 1°52’39” = 1.89°
Moon Picture Analysis
- Sensor size: 36mm × 24mm (Canon 6D, full frame)
- Lens: 70-200mm ×2 at 320 mm
- Field of view: 6.4° × 4.3°
- Horizontal angular diameter of the Moon from the image: 44px / 553px * 6.4° = 0.51°
- Angular diameter of the Moon from Stellarium (June 20, 2016): 30’28” or 0.51°
References
- Apollo 17 Mission Photography Overview – Universities Space Research Association
- Apollo 17 Image Library – NASA
- Reseau Plate – NASA
- Apollo 17 Index, 70 mm, 35 mm, and 16 mm Photographs – NASA
- Apollo17.org
- File:Astronaut Harrison ‘Jack’ Schmitt, American Flag, and Earth (Apollo 17 EVA-1).jpg – Wikipedia
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