Dawn

I have followed Jack Horkheimer's suggestion


This morning, 18 June, I observed the dawn from my home, as suggested by Jack Horkheimer, Star Hustler (as he once called himself). I put a lawn chair on my front garden, and sat in it from 3.15 to 4.30 am (Standard Time; Daylight time is one hour later), from the beginning of Nautical Twilight to Sunrise. I have a very bad observing position, as I have often stated. There are two high-pressure sodium lamps within 50 yards, one to the northeast and one to the southeast, which I try to keep behind trees. In addition, I saw 9-10 porch lights on up and down the street. People are scared of the dark here in the U.S., and waste as much energy on lights as they save by the rather futile recycling. It is impossible for the eyes to become dark-adapted in these surroundings. Check the brightness of the sky by holding your hand up in front of it.

The sky was completely cloudless, and the wind Force 0 (dead calm). The temperature was about 55°C, but was not measured exactly. The square of Pegasus and the three bright stars of Andromeda in the east, Fomalhaut low in the south, and the Summer Triangle of Vega, Deneb and Altair high in the sky, were evident. To the west was Arcturus, though I was not facing that way, and did not observe it. Nautical Twilight began at about 3.15 am. The dark trees to the east were outlined by a whitish glow in the northeast, where the sun would later rise. At this time, the separation of sky and sea would be visible on the ocean, and sextant measurements of the elevations of bright stars could be made. The stars of Andromeda would be an excellent choice, since they were in the direction where the horizon would first become evident, and high enough not to be affected seriously by refraction.

The first twittering of birds was heard about 3.30, probably sparrows some distance away. The birds do not all wake up at the same time. They are apparently seeing that everyone is awake and are forming foraging parties for the day. There was little traffic noise, but the ever-present white noise of a city was still there, but faint. A small propeller airplane droned its way insolently over the city northwards, probably on some selfish and inconsequential mission. Sirens were heard in the distance three times in the next ten minutes or so. There is no traffic, so they were purely acoustic swaggering by the authorities (the worst offenders are ambulance drivers, who like to make lots of noise on a totally empty street without traffic lights). The newspaper arrived at 3.45, thrown from an SUV, that went northwards throwing to my side (west) and then southwards a short while later, doing the other side. This is the first traffice since the milkman came by around 3.00.

It is getting lighter at 3.50, but Andromeda is still quite visible. The sky is a bluish-white, becoming less saturated and whiter steadily. It appears lighter in the west, around the roofs of the houses on the west side of the street. This may be a contrast effect of the light sky against the dark house silhouettes, not an actual lightening. However, Minnaert tells us of the counterglow, a result of the longer path to the horizon than overhead, sending us more light. However, Denver's light pollution may mask such subtle effects. A westbound jet leaves a short white contrail high in the sky. The air is very dry, and soaks up the condensation rapidly. The eastern horizon is becoming somewhat tawny. A bird flies to the northwest, and a dog barks pointlessly at 3.55, violating city ordnances. A bird flies southeast at 3.58.

It is now 4.00, and Civil Twilight is beginning. Objects around me are visible, and I can see my notepad easily. Only the brightest stars are still visible, such as Fomalhaut and Altair, but Andromeda is lost in the glare. The dawn chorus of the birds has increased in volume, and now seems to be approaching a maximum. The eastern sky is light, and has lost its saturation, becoming almost a dirty white. This may be an effect of a thin haze of smoke from the forest fires to the southwest. At 4.04, bats are seeen swooping and darting among the trees down the street, eating breakfast. At 4.05, crows begin to caw, 3, 4 or 5 times in each series, and the signals are answered. A bird flies southeast. At 4.10 the dawn chorus is at a maximum. All the stars, even Fomalhaut, have disappeared to the naked eye. A bird flies east, then a group of three northwest. The bats have stopped swooping, and one flies southwest on a straight line. A crow flies northwest, then a pair southeast at 4.13. A nearby crow caws insistently, and seems to be answered from a distance. A bat flies straight east at 4.15, then curves off to the north.

The sky is rapidly lightening generally, but it is a whitish, very unsaturated blue. Some dirty clouds appear in the northwest, and the wind rises to Force 1 from the south. A car travels south on the street at 4.18, and a crow flies southwest at 4.19. I notice a small bird hunting on the driveway opposite. A distant contrail appears as a thin dark stain to the east at 4.18. This jet passes overhead at 4.28, so it was perhaps 50 miles away when first sighted. By this time, the contrail has turned white, and even shows some tinges of sunlight. A second car passes south at 4.23, moving rather hesitantly. At 4.25, seven large birds fly southeast in formation, perhaps geese or ducks. Wispy clouds in the northeast are white. A long-tailed bird (probably a magpie) flies west overhead, then returns east a minute or so later. At 4.30, the wispy cloud is pinkish in sunlight, and a train is heard whistling to the north.

The sky is now a robin's-egg blue. A robin (thrush) is searching the driveway opposite for sustenance. Sparrows are in flight here and there, and come to search my driveway. The dawn chorus is subdued, nearly absent, and crows are no longer heard. It is sunrise, 4.30 by the clock, but nothing spectacular happens. I cannot see the horizon, but it is probably hazy. Direct sunbeams do not appear for about another quarter of an hour, and the sodium lamps finally go out at about 4.25. The illumination level at which they extinguish themselves is about 10 ft-cd. At 4.35, my neighbor comes out with his cats Maximilian and Howard and turns on the sprinkler. I did not see any cats earlier, which surprised me, nor any other small ground animals. I heard no gunshots or rattle of small arms, since the armed are usually asleep at this time.

It was a pleasant experience to observe the dawn and its happenings, even here in the city. The cost of admission is minimal. At sea or in the country it must be a wonderful show indeed. Sunsets are frequently observed, but sunrises only rarely by such as I. After the show, have a good breakfast and go to bed!

References

M. Minnaert, The Nature of Light and Colour in the Open Air (New York: Dover, 1954), pp. 287-290. Dawn is the best time to observe the fainter twilight phenomena, such as the Zodiacal Light, but this is impossible in a situation such as Denver's, of course, where even the Milky Way cannot be seen.


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Composed by J. B. Calvert
Created 18 June 2002
Last revised 19 June 2002