How far away would an object the size of an Apollo flag be visible with current telescopes?

1. Why the flag is invisible from Earth: angular size and diffraction

An object’s resolvability depends on its angular size at Earth and a telescope’s diffraction limit; a ~1–2 m flag at ~384,400 km subtends roughly 0.002 arcseconds or a few tenths of a milliarcsecond, far smaller than what current telescopes can resolve in visible light ^{[5] [3]}. Practical calculations using the Rayleigh criterion show that resolving a meter‑scale feature at lunar distance would demand apertures on the order of tens to a few hundred meters (estimates in the reporting range from ~85 m up to ~240 m depending on wavelength and assumptions), and no such single mirror exists ^{[3] [6] [7]}.

2. What the best existing telescopes can actually do

Hubble, with a 2.4 m mirror, has a lunar resolution on the order of ~100 meters per resolvable feature, meaning it can distinguish football‑field scale structures but not meter‑scale items like flags ^{[1] [2] [8]}. Large ground telescopes with adaptive optics (like Keck, ~10 m class) improve on older instruments but remain orders of magnitude short of the aperture needed to image flags directly; practical ground‑based resolution is further limited by atmospheric turbulence despite adaptive optics ^{[3] [7]}.

3. Interferometry and hypothetical arrays: theory vs practice

In principle, interferometric arrays or widely separated mirrors can synthesize very large apertures and reach the needed angular resolution — some back‑of‑envelope discussions show baselines of hundreds of meters to kilometers might approach meter‑scale resolution at lunar distance ^{[6] [9]}. In practice, interferometric imaging of an extended, bright, high‑contrast lunar surface is extremely challenging and not currently configured to map lunar artifacts; proposals like the not‑built Overwhelmingly Large Telescope were projected to reach only ~10–20 m resolution at best ^[9].

4. Spacecraft win by being close: LRO and direct imaging

The only practical way to “see” Apollo flags is to go close enough: NASA’s Lunar Reconnaissance Orbiter carries cameras capable of sub‑meter imaging from lunar orbit and has photographed the Apollo landing sites, resolving lander bases, rover tracks and shadows consistent with flags and disturbed soil ^{[2] [10] [4]}. Reporting stresses that orbital imaging is the definitive evidence for the artifacts rather than Earth‑based telescopes ^{[2] [4]}.

5. Common numerical claims and why they vary

Public sources quote required telescope diameters varying from ~85 m to ~200–240 m to see flags; the spread reflects differences in assumed flag size (1–2 m), chosen wavelength, diffraction‑limited vs atmosphere‑limited performance, and whether one assumes a single aperture or interferometric baseline ^{[3] [7] [6] [11]}. All sources converge on the qualitative point: current telescopes (Hubble, Keck, JWST, and ground observatories) are orders of magnitude too small or not configured to resolve meter‑scale artifacts at lunar distance ^{[1] [3] [2]}.

6. Bottom line and alternate viewpoints

Bottom line: from Earth, no current telescope can directly resolve an Apollo flag; doing so would require an aperture or effective baseline in the tens-to-hundreds‑of‑meters range that we do not have for lunar surface imaging ^{[1] [3] [7]}. The responsible alternative viewpoint is that advanced interferometry or a purpose‑built massive array could, in theory, achieve the resolution, but those are concept‑level ideas, not operational facilities — and they would face engineering and atmospheric challenges before delivering useful lunar images ^{[9] [6]}.