July Sky – The Twilight Zone

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by Pat Browne

July is a difficult month to ramble through the skies at night. We (observers at northern latitudes) get so little darkness, and what we do get, we have to share with the mosquitos!

they’re coming to take you away…

Mid-Month Times for Sunset, Civil twilight, Astronomical Twilight

Jul 15 2017 – data courtesy National Research Council Canada
Sunset: 20:48
Civil Twilight End: 21:24
Nautical Twilight End: 22:11

(Time zone is EST, -5 UTC Correction from standard meridian : 3.00 minutes)

Astronomical Twilight : (Sun is 18° below the horizon) ends at 23:07. That means it’s past 11 o’clock before  we get true night time darkness!

Longer Days:

 

Sun stays above the horizon longer in July in the northern hemisphere

So our ramble this month will take us instead to two narratives of July in the twilight zone:
  • George Lovi, 1973 Sky and Telescope: Rambling Through the July Skies
  • Eric Steinbring’s travel experience in the Canadian Arctic… as presented at this year’s RASC (Royal Astronomical Society of Canada’s) General Assembly in Ottawa.
Rambling Through The July Skies

George Lovi writes…

“The long summer twilight of northerly observers was much on my mind … [on a flight ] Passing Alaska during our “night” period we headed eastward through several time zones which converge strongly at high latitudes. The northern horizon had a continuous twilight glow, and I estimated that the sun was never more than a dozen degrees below the horizon. I saw 4th magnitude stars in a virtually dark sky yet the horizon glow was bright… Shortly thereafter the stars to the north appeared just as they do above the 50° northern horizon on this month’s chart. Perseus, Cassiopeia, and Auriga were prominently placed…

Reprint from 1973 Sky and Tel – click to enlarge
click to enlarge

George Lovi continues…
“The midnight sun and associated twilight phenomena will repay study by amateur astronomers… An instructive astronomy laboratory project is to have students work out the number of midnight-sun days [or mid-day dark days] , the “day” refers to the time when the sun is above the horizon, “night” to when it is below, without regard to twilight…”

Rambling through the Canadian Arctic in-between the Twilight zones…

It turns out, there is some very interesting science laboratories in the Canadian Arctic. Astronomers set up their experiments in Summer and begin to collect uninterrupted data as the daily altitude of the Sun eventually dips for many hours below the horizon in mid-winter for  ‘long days journey into night’.

On Ellesmere island, 80°N. The Arctic Cordillera mountain system covers much of Ellesmere Island, making it the most mountainous in the Canadian Arctic Archipelago. Astronomical data collection on these mountains in day-dark winters promise excellent ‘astronomical ‘Seeing’ conditions with increased resolution produced by ‘adaptive optics’

This year’s  RASC General Assembly  hosted by the Ottawa Center delighted everyone with the special Ruth Norcott Lecture  given by astronomer  and Canadian Arctic trave[b]loger …

The RASC hosts the biennial Ruth Northcott Memorial Lecture in conjunction with its annual General Assembly. This lecture is offered to the general public, and can cover any facet of ‘cool’ astronomy. For those of us who missed it, thanks to our Ottawa RASC videographer, Eric Kujala, we can follow along with the lecture on Astronomy in Canada from Coast to Coast …(to Coast)