The fol­low­ing arti­cle is a tran­script of the video above. 

Hi there, my name is Paul, and this is Expo­sure Ther­a­py. In this video, I’ll explain why your pho­tos of the moon are often over­ex­posed and how you can fix them. 

It’s sunny on the Moon

I teach group pho­tog­ra­phy work­shops, and occa­sion­al­ly, stu­dents will ask some vari­a­tion of the fol­low­ing ques­tion:

I tried tak­ing a pic­ture of the full moon last week, but it turned out too bright and fea­ture­less. How do I take pho­tos of the Moon, so it looks sim­i­lar to how my eyes see it?

My typ­i­cal (and slight­ly cheeky) response is to point out that it’s sun­ny on the moon. Then I wait for a beat or two to let it sink in. 

Is it sink­ing in for you?

Moonlight and sunlight

Let’s begin with the basics. The moon and the sun are the most promi­nent celes­tial bod­ies in the sky. An impor­tant dis­tinc­tion between the two is the nature of their light. The sun radi­ates its light—it glows. It’s sim­i­lar to the flames of a fire, neon signs, and the tung­sten fil­a­ments of light­bulbs. By con­trast, moon­light is sun­light that has bounced off its sur­face to end up on Earth, both in our eyes and our cam­eras. 

The problem with measuring light

Con­ven­tion­al­ly, the most reli­able way to get the “cor­rect” expo­sure of sub­jects that don’t glow is by using an inci­dent light meter, such as this Sekon­ic that I’ve had for 15 years. These devices mea­sure the amount of light falling on your sub­ject. I walk up to my sub­ject, point the white dome towards the cam­era, take a light read­ing, and the meter shows the cor­rect expo­sure set­tings for the scene.

How­ev­er, there’s an obvi­ous flaw with this method: with its aver­age orbital dis­tance of about 385,000 km, one does not sim­ply walk up to the moon. 

So what do we do? We remem­ber that it’s sun­ny on the moon. But let me qual­i­fy that state­ment.

Lunar phases

Except for lunar eclipses, sun­light illu­mi­nates half of the moon’s sur­face at any giv­en moment. How­ev­er, there’s a dai­ly change to the appar­ent shape of the sun­lit por­tion of the moon as seen from Earth. These dif­fer­ences in appear­ance, known as lunar phas­es, occur because as the moon orbits the earth, we see vary­ing amounts of its sun­lit half. 

New moon

The moon is not vis­i­ble dur­ing the new moon phase when it’s rough­ly between the earth and the sun. The new moon is invis­i­ble because it’s in the same part of the sky as the sun, and its “near side” — the hemi­sphere that always faces the earth, regard­less of phase — is in com­plete shad­ow. 

As the moon con­tin­ues its orbit, pro­gres­sive­ly more of its near side turns towards sun­light. First, it becomes a wax­ing cres­cent moon, then a first-quar­ter moon, fol­lowed by a wax­ing gib­bous moon, cul­mi­nat­ing in a full moon. 

Full moon

Dur­ing a full moon, Earth is rough­ly between the moon and sun. The full moon is com­plete­ly vis­i­ble because it’s oppo­site the sun in the sky, and the hemi­sphere of its near side is in full sun­light. 

The lunar phas­es con­tin­ue in reverse beyond the full moon as its near side grad­u­al­ly turns away from the sun. These phas­es are wan­ing gib­bous moon, last quar­ter moon, wan­ing cres­cent moon, and then a new moon. The peri­od from new moon to new moon marks an entire lunar month, which takes 29.53 days to com­plete, and is equiv­a­lent to a sin­gle day/night cycle on the moon.

Daylight is a surrogate for sunlight on the moon

We’ve estab­lished it’s sun­ny on the moon and that we see vary­ing amounts of the sun­lit hemi­sphere through­out a lunar phase cycle. But we still have the prob­lem of not get­ting close enough to the moon to get an expo­sure read­ing. The solu­tion, as earth­bound pho­tog­ra­phers have fig­ured out long ago, is tak­ing an inci­dent read­ing from some­where that’s with­in reach and has light iden­ti­cal to their subject’s posi­tion. 

It’s sun­ny on the moon, but it’s also sun­ny here on Earth. To take pic­tures, it’s entire­ly rea­son­able to assume that after­noon sun­light on Earth is iden­ti­cal in inten­si­ty to sun­light on the full moon. There­fore, expo­sure set­tings appro­pri­ate for direct after­noon sun­light on Earth will pro­duce cor­rect expo­sures of the full moon at night. 

This is why photos of the moon at night are overexposed

Any­one who’s tried tak­ing pho­tos of the moon at night using their camera’s auto­mat­ic set­tings has prob­a­bly found the results dis­ap­point­ing. Most auto­mat­ic pho­tos of the moon at night are irrepara­bly over­ex­posed, and there are two rea­sons why. First, the moon is hun­dreds of times brighter than the sur­round­ing night sky. And sec­ond, although this bright­ness gives it visu­al promi­nence, its scale with­in most pho­to­graph­ic com­po­si­tions is rel­a­tive­ly tiny at typ­i­cal focal lengths. Togeth­er, these fac­tors cause the cam­era to assume it’s tak­ing a pho­to of some­thing quite dark, and it com­pen­sates by let­ting in far more light than your intend­ed sub­ject requires, which wash­es out the moon. 

The best way to get “cor­rect” expo­sures of the moon at night is by tak­ing com­plete con­trol of your cam­era using man­u­al mode. But what qual­i­fies as a “cor­rect” expo­sure?

The moon is darker than you think

Even when it’s not over­ex­posed, many pho­tos of the night­time moon ren­der it brighter than its true light­ness. In astron­o­my, “albe­do” describes the aver­age sur­face reflectance of plan­ets, moons, and aster­oids. Albe­do mea­sures the frac­tion of inci­dent light the sur­face reflects in all direc­tions. The moon has an albe­do of 0.12, which means it reflects just 12% of the Sun’s light. This trans­lates to an aver­age sur­face light­ness described as slight­ly brighter than old asphalt. In com­par­i­son, Earth’s albe­do aver­ages to about 0.30. The pho­tos tak­en by the crews of NASA’s Apol­lo land­ings show just how dark the lunar sur­face appears in com­par­i­son to the astro­nauts’ white space­suits in direct sun­light. 

The pur­pose of the Apol­lo pho­tos was to cre­ate an accu­rate visu­al doc­u­ment of the lunar sur­face, its fea­tures, and of the astro­nauts and their equip­ment. 

 Since earth­bound pho­tog­ra­phers don’t have such mis­sion-crit­i­cal con­straints, we’re free to take cre­ative license in our depic­tions of the moon. Some pho­tog­ra­phers choose accu­rate depic­tions. Oth­ers pre­fer rep­re­sen­ta­tions that are brighter than true while ensur­ing sur­face details aren’t washed out. And a third group doesn’t care because their pri­ma­ry sub­ject is some­thing else, such as the moon­lit land­scape. Hence, every men­tion of “cor­rect” expo­sures fea­tures scare quotes. I believe that with­in the art of pho­tog­ra­phy, every expo­sure is cor­rect so long as a result is inten­tion­al. An expo­sure is only wrong when the effect is unde­sir­able. 

The lunar phase affects brightness

The moon’s phase affects how bright it appears on Earth. The illu­mi­nat­ed por­tion of the moon looks bright­est dur­ing the full moon and dark­est dur­ing the cres­cent moon. As our angle of view rel­a­tive to the sun decreas­es, the moon’s high­ly crat­ed and irreg­u­lar sur­face forms a greater amount of shad­ows as seen by observers from Earth. This low­ers the sur­face reflectance of the sun­lit por­tion vis­i­ble to us. 

Addi­tion­al­ly, the full moon appears brighter due to a phe­nom­e­non called oppo­si­tion surge. It occurs when a rough sur­face appears brighter when the light source is direct­ly behind the observ­er. The Apol­lo mis­sions pro­vide human-scale exam­ples of this effect in their pho­tos from the sur­face. The surge in bright­ness is quite sub­tle due to its gra­da­tion and the impact of colour con­stan­cy. The dif­fer­ence in bright­ness becomes rather stark when mak­ing a side-by-side com­par­i­son of two non-adja­cent patch­es of lunar soil. In some pho­tos, the effect is also notice­able on a small scale in the reflec­tions of astro­nauts’ hel­mets. In this famous exam­ple, the oppo­si­tion surge bright­ens the area around Buzz Aldrin’s shad­ow, as seen in his helmet’s reflec­tion. And here, we see it in the reflec­tion of David R. Scott’s shad­ow from Apol­lo 15. On a macro scale, the entire vis­i­ble sur­face of the moon expe­ri­ences an oppo­si­tion surge of bright­ness dur­ing the full moon phase. 

Lunar altitude affects its brightness and colour due to atmospheric light scattering

Regard­less of the lunar phase, the moon’s bright­ness and colour are also affect­ed by its alti­tude, which describes the appar­ent height of a celes­tial object above the hori­zon. It’s expressed in degrees, with the hori­zon at 0° and the zenith (direct­ly over­head) at 90°. 

The moon appears brighter at pro­gres­sive­ly high­er alti­tudes. The sun exhibits the same char­ac­ter­is­tics: sun­light is harsh­est at solar noon and faintest at sun­set. In both cas­es, the atmos­pher­ic scat­ter­ing of light caus­es the effect. 

Light scat­ter­ing occurs when pho­tons bounce off par­ti­cles in their paths, such as atoms and mol­e­cules. Par­ti­cles that are small­er than the wave­length of vis­i­ble light are more effec­tive at scat­ter­ing the short-wave­length pho­tons of blue light than the long-wave­length pho­tons of red light. 

Light scat­ter­ing occurs at all alti­tudes. When the moon or sun is near the hori­zon — either ris­ing or set­ting — the light reach­ing your eyes pass­es through a thick lay­er of the atmos­phere, which scat­ters a far more sig­nif­i­cant amount of blue light than red. Since a large por­tion of their light is scat­tered away from a straight-line path to your eyes when they’re near the hori­zon, they appear red­der. At high­er alti­tudes, the moon’s light pass­es through a com­par­a­tive­ly thin lay­er of the atmos­phere, scat­ter­ing just enough blue light to give the Moon its char­ac­ter­is­tic yel­low­ish colour, dis­tinct from the stark grey sur­face depict­ed in the Apol­lo pho­tos. 

As an inter­est­ing side note, if you’re an ear­ly bird, you’ve prob­a­bly noticed that sun­ris­es are less red than sun­sets. That’s because there’s a greater propen­si­ty for stronger winds dur­ing the day­time, which helps lift dust par­ti­cles into the atmos­phere and scat­ters even more blue light. The same effect doesn’t nec­es­sar­i­ly apply to the set­ting and ris­ing of the moon. I’ve per­son­al­ly wit­nessed many red­dish moon­ris­es; how­ev­er, they’ve all occurred close to sun­set, while dust per­me­at­ed the local atmos­phere.

All of this relates to tak­ing pho­tos of the moon. Expo­sure set­tings derived from mid-after­noon day­light are gen­er­al­ly cor­rect for pic­tures of a full-ish moon at an alti­tude of 45° or greater (that is, more than halfway up between the hori­zon and zenith). How­ev­er, these set­tings will like­ly be incor­rect for pho­tos of the moon while it’s near the hori­zon since Earth’s atmos­phere atten­u­ates much of its bright­ness. 

Crescent moons and earthlight

Have you ever gazed upon a cres­cent moon and real­ized that you could see details in its shad­ed por­tion?

Much as with the moon, some sun­light that strikes Earth’s sur­face and clouds reflects into space. This reflect­ed light is called earth­light. The sub­tle illu­mi­na­tion of the Moon’s dark side by earth­light is called earth­shine. The dis­tinc­tion between these two terms can be con­fus­ing at first, but it’s all quite sim­ple if illus­trat­ed with a dia­gram. Light from the sun is sun­light. Sun­light reflect­ed by the earth is earth­light. Earth­light reflect­ed off the moon’s dark side is earth­shine. [Use a vari­ant of this dia­gram: https://upload.wikimedia.org/wikipedia/commons/3/3f/Earthshine_diagram.png]

Earth­shine is most promi­nent­ly vis­i­ble dur­ing the moon’s cres­cent phase. An observ­er stand­ing on the moon’s near-side would see a very bright “gib­bous Earth” against the black sky. At this point, you should come to the grad­ual real­iza­tion that the moon expe­ri­ences Earth in phas­es, and these phas­es are com­ple­men­tary. Thus, a new moon on Earth coin­cides with a full earth seen from the Moon, and so on. Earth­shine peaks dur­ing the new moon but remains invis­i­ble because of the moon’s prox­im­i­ty to the sun in the day­time sky.  

Tak­ing pho­tos of earth­shine using your camera’s auto­mat­ic mode should give decent results because earth­shine is clos­er in bright­ness to the typ­i­cal night or twi­light sky. How­ev­er, a sin­gle expo­sure can’t cap­ture detail in both because the dif­fer­ence in bright­ness between earth­shine and the sun­lit por­tion of the moon is too sig­nif­i­cant. Against a dark sky, your cam­era will over­ex­pose the cres­cent.

How to take photos of the moon at night

The point of this video is to explain the futil­i­ty of a sin­gle solu­tion. That’s because the moon’s bright­ness varies with its phas­es and alti­tude. More­over, the accu­ra­cy of your expo­sure to the moon’s true light­ness is also an artis­tic deci­sion. The solu­tion requires inter­nal­iz­ing a fun­da­men­tal prin­ci­ple: it’s sun­ny on the moon. 

How­ev­er, for those of you inclined to pre­scrip­tive rec­om­men­da­tions, start with expo­sures appro­pri­ate for the full moon high in the sky and incre­men­tal­ly work your way down to dim­mer moons.

Select man­u­al shoot­ing mode, and choose appro­pri­ate expo­sure set­tings for a sub­ject in direct after­noon sun­light on earth. At ISO 200, this means select­ing ƒ/5.6 and 1/2000s, or ƒ/8 and 1/1000s, or ƒ/11 and 1/500; all of these dif­fer­ent set­tings pro­duce the same expo­sure. When the moon is low­er in the sky or dur­ing a minor phase, increase your expo­sure by select­ing a low­er f‑number or slow­er shut­ter speed, or both. Expe­ri­ence and prac­tice using your cam­era make the process faster and eas­i­er. How­ev­er, it would help if you start­ed from the prin­ci­ple that it’s sun­ny on the moon.

Conclusion

I hope you found this video inter­est­ing and help­ful. I enjoy talk­ing my stu­dents through these types of ques­tions instead of stat­ing the cor­rect set­tings with­out explain­ing why they’re right. If you have requests for top­ics, let me know in the com­ments, and I’ll con­sid­er them for future videos. In the mean­time, you can learn more about pho­tog­ra­phy or join my group work­shops in Toron­to by vis­it­ing ExposureTherapy.ca. See you next time.