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    Alnair identification
    From: Frank Reed
    Date: 2023 Oct 31, 10:57 -0700

    The navigation star Alnair (formerly spelled Al Na'ir in the official Nautical Almanac star list) is moderately bright but not well-known in northern latitudes since its Dec is nearly -47°. Yet even from my latitude in southern New England where it barely makes it above the southern horizon when transiting the meridian, it happens to be relatively easy to identify thanks to the "neck of the crane". Yes... there's a crane in the sky.

    The constellation Grus is a crane, a bird with a long neck, and Alnair is the brightest star in the constellation, and its Bayer designation is α Gruis (that's "alpha" Gruis). Here's a nice photo I came across on Friday. It is tagged as having been taken from Suwarrow Atoll in the Pacific Ocean. After passing right over Machu Picchu in Peru this past Saturday morning, the Sun also passed directly over Suwarrow about six hours later. This is an uninhabited atoll in the mid-Pacific near 163° West and 13° South which is administered by New Zealand.

    Notice the string of star pairs near the top of the photo. That's usually identified as the neck of the "crane" in the constellation Grus. Once you've seen them a few times, these are easily spotted in the sky, or in a night sky photo, and they lead directly to Alnair. You may also be able to find the nav star Peacock in the photo of this ornithological stretch of the night sky...

    So... is the photo consistent with the view from Suwarrow Atoll? Assuming the latitude is about right, then what is the approximate Sidereal Time or equivalently the SHA of the meridian implied by the photo. And if I tell you that the date is 1 January 2019 (it isn't, but just for discussion), then what is the UT for this photo?

    Frank Reed


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