Tag Archives: astronomy

Seeing Stars on the Moon

Why don’t moon photos show stars?. Specifically, why can’t we see the stars in the photographs of the Apollo Astronauts on the moon? As the article clearly explains, all of the pictures were taken during lunar daylight, during which the lunar surface is well illuminated by the sun. This completely washes out the light from the stars. If you made a long enough exposure to catch the stars, the lunar surface, the astronauts and their gear, and the lunar lander would be grossly overexposed. This would defeat the purpose of documenting human activity on the moon.

In fact, this issue was anticipated by Arthur C. Clarke in his classic science fiction novel A Fall of Moondust, first published in 1961, eight years before the first Apollo expedition landed on the moon. Continue reading

Web Site Updates

I fixed some dead links and made other minor corrections and updates, but did not make any drastic changes in the longer pieces, so their style reflects the times when they were written, years or even decades ago. However, I think they are still relevant to the subjects being discussed.

Chicon 8

Thursday

On Thursday, Sept. 1, Mia McDavid and I drove to Chicago for Chicon 8: The 80th World Science Fiction Convention at the Hyatt Regency Chicago . This was our 5th Chicon. Previously we had attended:

Despite some glitches, we really enjoyed the Con, and visiting downtown Chicago again.

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Rang Gaeilge, 23ú lá Mí Feabhra 2022

Duinnín i Ráth Maonais (tuilleadh)

  • ‘Rachaidh mé féin anseo isteach, ‘arsa an Duinníneach nuair
    a shroicheadar an eaglais. ‘Ba mhaith liom cúpla focal a bheith
    agam le Tom Merrigan.’

    Tharla cruinniú coiste de chuid bhuanchoiste an aonaigh
    saothair ar siúl ar ardán an halla nuair a bhuail an Duinníneach
    isteach agus bhí an tAthair Merrigan ag déanamh eadrána idir
    seastán na gcístí agus lucht roth an áidh. Chuir sé na mná uaisle
    ar fad in aithne don Duinníneach, a gheall go dtiocfadh sé chun
    aonaigh agus go gceannódh sé stocaí bána cniotáilte uathu dá
    mbeidís ar fáil. D’éalaigh siad on gcruinniú ansin agus shiúil
    siad thart ar an halla, idir na stainníní, agus iad ag caint.

    ‘I’ll go in here myself,’ said Dineen when they reached the church.
    ‘I would like to have a few words with Tom Merrigan.’

    A meeting of the standing committee of the job fair was taking place on the hall stage
    when Dineen came in and Father Merrigan was mediating between the cake stand and
    the wheel of fortune. He introduced all the ladies to Dineen, who promised to come to the
    fair and buy white knitted socks from them if available. They then escaped from the meeting and walked around the hall, between the booths, talking.

    coiste jury, committee m
    buanchoiste Standing committee m
    ardán platform, stage, stand m
    eadráin Separation of combatants; intervention in dispute; mediation, conciliation f gs eadrána
    seastán stand m
    roth wheel n
    ádh luck m gs áidh
    lucht Content, charge; fill, capacity; cargo, load;
    Class, category, of) people
    m
    geall pledge, security m
    stainnín Stand, stall, booth m
  • Léigh tuilleadh

    Capricon Notes

    As I wrote previously , Mia (my wife) and I spent last weekend at Capricon, a Chicagoland science fiction convention. We went to most of the Capricons in the ’80’s and ’90’s, but in our first years in Minnesota the pressures of parenthood prevented us from going. Those have eased somewhat and we have been to most of the Capricons (and Windycons) since 2009. While most Capricons have been in the Chicago suburbs, this year the convention was downtown, at the Sheraton Grand Hotel.

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    Black Hole Lifetimes

    Black holes are not totally black! They will evaporate by Hawking radiation. This is required by Thermodynamics and Quantum Mechanics. All properties of a Schwarzschild black hole are determined by its mass, so if you know the mass the lifetime and other properties follow automatically. Or you can start with the lifetime and determine the initial mass. Or the Schwarzschild radius, or the temperature, or the entropy, etc. For black holes comparable in mass to “normal” astronomical objects this lifetime is much longer than the current age of the universe. Viktor Toth’s Hawking radiation calculator is a convenient tool for such calculations. Here are some results:

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    Blinking Astronomical Photographs

    Low-Cost Approach to Scanning Historic Glass Plates Yields an Astronomical Surprise. Technical details at Precise Photometric Measurements from a 1903 Photographic Plate Using a Commercial Scanner.

    Professional astrophotography used to be done on emulsion-coasted glass places. That was how astromical discoveries were made for nearly a century.

    More than an estimated 2.4 million glass plates are out there in collections in North America alone. These were taken starting in the 1890s right up until the 1970s, when CCD (Charged Couple Device) detectors started to come online for astronomy. Of these, only an estimated 400,000 plates have been digitized to research quality

    The team in this article has found a much cheaper way to proceed with this process, using off-the-shelf hardware.

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