Nature’s own triumphal arch

Originally published 9 January 1989

With snowflakes in the air, this may seem to be the wrong time of the year to be writ­ing about rain­bows. But I’ve just read for the sec­ond time Fred Schaaf’s essay “100 Rain­bows” in his new book The Star­ry Room, and I’m remind­ed that rain­bows are not nec­es­sar­i­ly a sea­son­al phenomena.

For five years Schaaf wrote the “Eye on the Sky” col­umn for Astron­o­my mag­a­zine, and he con­tin­ues to be the astron­o­my essay­ist for The Old Farmer’s Almanac. He is a gift­ed observ­er of things in the sky — mete­ors, comets, plan­ets, stars, and oth­er celes­tial lights.

Among oth­er things, Schaaf is a rain­bowol­o­gist, if such a thing exists. He is a col­lec­tor of rain­bows, and he knows you don’t need a sum­mer rain to see a rain­bow in the sky. Among the 100 dif­fer­ent kinds of rain­bows he lists in his essay are the “rain­bow cut off by falling snow” and “rain­bow over a snowy landscape.”

Snowflakes can­not pro­duce a rain­bow, only drops of water can do that. But it is not impos­si­ble to have snowflakes and drops of water in the same field of view at the same time. Even in sum­mer­time snow some­times occurs high up in rain clouds, and the flakes can ter­mi­nate the arc of a rain­bow. Schaaf reports see­ing such a thing. And of course a water­fall can make a spray of bow-pro­duc­ing mist in a land­scape of snow. I saw a bow this bright win­ter morn­ing while mist­ing the houseplants.

Learning the signs

The kind of rain­bow most of us have seen is called a pri­ma­ry bow. It is vis­i­ble when the sun is shin­ing at your back, low in the sky, and there is rain in front of you. I have occa­sion­al­ly sur­prised friends by suc­cess­ful­ly fore­telling the pre­cise moment and loca­tion of a beau­ti­ful bow, but if one has seen enough rain­bows it is easy to pre­dict when the right con­di­tions are about to occur. Schaaf says he some­times calls peo­ple on the tele­phone to tell them a rain­bow is head­ing their way.

There are lots of vari­a­tions on the pri­ma­ry bow, and Schaaf lists them all. The not-uncom­mon sec­ondary rain­bow is usu­al­ly fainter and out­side of the pri­ma­ry bow, with the order of col­ors reversed. Sec­ondary bows are caused by a sec­ond reflec­tion of sun­light with­in the rain­drop before it emerges. A third reflec­tion in the rain­drop pro­duces a ter­tiary rain­bow, but these are rare and sel­dom seen.

Schaaf lists the most dis­tant nat­ur­al rain­bow he has heard about (80 miles) and the near­est (three yards). He gives sep­a­rate entries in his list to rain­bows seen at sun­rise or sun­set, a rain­bow with light­ning strik­ing through it, a rain­bow shak­en by thun­der, and a rain­bow seen in con­junc­tion with the moon. In fact, Schaaf lists so many beau­ti­ful pos­si­bil­i­ties that the prover­bial pot of gold at the rain­bow’s end begins to seem a less desir­able reward than the rain­bow itself.

Some places are bet­ter for rain­bow watch­ers than oth­ers, and New Eng­land is not the best, even in sum­mer. Those of you who are going south for a win­ter vaca­tion will be less upset by rain if you look for the gen­er­ous­ly pro­vid­ed trop­ic bows. Schaaf says there are places in the Hawai­ian Islands where rain is unceas­ing and in ear­ly win­ter, when the sun is low in the sky, a rain­bow can be watched all day long.

In the eye of the beholder

I spend part of every year in south­west Ire­land, a superb place for an ama­teur rain­bowol­o­gist. Once I saw four rain­bows in a sin­gle day, sure­ly not a record but an achieve­ment of which I am proud. With so many rain­bows to observe it soon becomes obvi­ous that no two bows are the same. Even the promi­nence of col­ors in the spec­trum varies from rain­bow to rain­bow, depend­ing on the size of the water droplets pro­duc­ing the bow.

Strict­ly speak­ing, every­one who looks at a rain­bow sees a dif­fer­ent bow. Rain­bows don’t exist out there, like a tree or a star, to be seen alike by every observ­er. Rain­bows exist only on the reti­na of an eye, and every observer’s eyes have a dif­fer­ent pos­ture with respect to rain and sun.

Almost any source of light and any kind of mist can pro­duce a bow of sorts. Schaaf lists rain­bows you can see at any sea­son of the year — mist­bows, fog­bows, cloud­bows, dew­bows, gey­ser­bows, and bows in the spray of a gar­den hose or lawn sprin­kler. He includes among his 100 rain­bows those caused by search­lights, street­lights, light­ning, and even vol­canic light.

There is more to Schaaf’s book than rain­bows. The sub­ti­tle of the book is “Naked Eye Astron­o­my in the Inti­mate Uni­verse.” The author knows you don’t need a tele­scope to do astron­o­my. The sky abounds with phe­nom­e­na — won­der­ful lights of all kinds, at all sea­sons, day and night, avail­able to every­one. Schaaf’s list of 100 rain­bows is just a taste of what is there to be seen, and his delight­ful essays are an irre­sistible invi­ta­tion to go look.

Every year around Christ­mas time I am asked for rec­om­men­da­tions by peo­ple who want to buy a tele­scope as a gift for a child or spouse. My advice is usu­al­ly, “don’t.” Unless one is will­ing to pay more than a few hun­dred dol­lars, the tele­scope will pro­vide more frus­tra­tion than plea­sure. And unless one is already rea­son­ably famil­iar with the sky, even an expen­sive instru­ment will tend to sit idle in the base­ment or garage.

That’s the valu­able les­son of Schaaf’s book: An ama­teur astronomer, mete­o­rol­o­gist, or rain­bowol­o­gist needs only a good pair of eyes to get on inti­mate terms with the universe.