SKYLIGHTS

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Photo of the Week.. Thundercloud.


Astronomy news for the two weeks starting Friday, August 11, 2017.

Prepared by Jim Kaler.

Clear skies and thanks to Skylights' blogger visitor reader.


Go to STARS for previous stars of the week. Last week's Skylights is still available. Access Skylights' Archive and photo gallery. From the Sun to the Stars: the OLLI Lectures provides a linked, illustrated introduction to astronomy.
The Constellations has a linked list with locations and brightest stars. Constellation Maps show the locations of the constellations. The 170 Brightest Stars lists them through magnitude 3.00. For more on stars and constellations, visit Stellar Stories.
Tour the Milky Way. Watch a total eclipse of the Moon and an annular eclipse of the Sun. Moon Light presents scenic photos of the Moon. Go to MoonScapes for labelled telescopic images of the Moon and other lunar information.
See the Moon move and pass just below Nu Virginis. Watch planets move against the background stars. See a classic proof of the curvature of the Earth with a "hull down" series. Visit Measuring the Sky to learn about the celestial sphere.
Admire sunsets, rainbows, and other sky phenomena in Sunlight. Read the illustrated Day Into Night on the phenomena of the sky See the The Aurora and the Midnight Sun. See and understand the ocean tides.
Enjoy Our Complex Universe: A Human Understanding through Art, with 12 illustrations. Advances in Astronomy, 1989-2011. Take a ride aboard Asteroid 17851 Kaler (1998 JK). Look for Books about the sky and stars.

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ASPSupport science literacy by joining the Astronomical Society of the Pacific, an international organization that is among the world's premier providers of astro education. Get Mercury and a variety of other benefits.


Presenting three audio courses with 70 to 100-page study guides, narrated and written by Jim Kaler.
Heavens Above: Stars, Constellations, and the Sky from Recorded Books. Astronomy: Earth, Sky, and Planets, is available from Recorded Books. Astronomy: Stars, Galaxies, and the Universe, is also now available from Recorded Books.
Astronomy: Earth, Sky, and Planets is published as Vault of the Heavens: Exploring the Solar System's Place in the Universe by Barnes and Noble.

Enjoy Our Complex Universe:A Human Understanding through Art, with 12 illustrations.

Read "Heaven's Touch: From Killer Stars to Seeds of Life, How We Are Connected to the Universe," Princeton University Press, now in Chinese translation.

SSTo learn about stellar spectra, read STARS AND THEIR SPECTRA: An Introduction to the Spectral Sequence, Second Ed., with two new chapters and 140 new illustrations, Cambridge University Press (UK or North America), 2011.


SSLive in town? Read FIRST MAGNITUDE: A Book of the Bright Sky, World Scientific, 2013. See the interview with Jim Kaler.


NEW! Read Dust to Dust in Stellar Stories.

NEW! From the Sun to the Stars: the OLLI Lectures, which provides a linked, illustrated introduction to astronomy.


IT'S HERE!, From the Sun to the Stars by Jim Kaler, World Scientific, 2016, a new book based on From the Sun to the Stars: the OLLI Lectures, which provides a linked, illustrated introduction to astronomy.



The next Skylights will be presented Friday, August 25, 2017.

Well, here it is, or there it goes, what we've all been waiting for, a spectacular total eclipse of the Sun on August 21, in which the path of totality runs diagonally across the US from near the Washington-Oregon border, through southern Illinois, to South Carolina. The path is very narrow. At best, totality (the Moon completely covering the Sun) lasts for two minutes and 40 seconds. The event begins as a partial phase around 11:53 AM CDT, the center of totality taking place at 1:21 PM, CDT. Times vary with location.

***DO NOT LOOK DIRECTLY AT THE BRIGHT SUN WITHOUT FILTERING GLASSES; DO NOT MAKE YOUR OWN. AS LONG AS ANY PORTION OF THE BRIGHT SUN ITSELF IS PRESENT, EYE DAMAGE CAN OCCUR. ***

As soon as the bright photosphere of the Sun is completely covered and we are within total shadow of the Moon you can look safely without aid and see the corona (the hot, thin outer solar atmosphere) and too many other phenomena to list here. Good luck and clear skies to all. Clear highways too, as the traffic may get mighty heavy. All the rest of the United States and Canada will see just the partial phase, with the Moon only partially covering the Sun. No other solar phenomena can be seen during the partial phase and you must still use your eclipse glasses to watch the Moon take a partial bite out of the Sun.

The Moon goes through perigee, where it is closest to the Earth, on Friday the 18th. If it were closer to apogee, the Moon would not cover the Sun and we would witness only an" annular eclipse," a mere ring of sunlight around the Moon.

After all this it's rather anticlimactic to go back to the night sky. At least we know that new Moon occurs during the day on August 21, since it is exactly between us and the Sun. Prior to the eclipse you can watch the Moon go through its third quarter on Monday the 14th, and then approach the Sun as a slimming crescent. It will make a lovely paring with Aldebaran in Taurus the morning of Wednesday the 16th. Following the eclipse, the waxing crescent will be visible in western evening twilight the night of Tuesday the 22nd. The crescent Moon will be to the southwest of Jupiter the night of Thursday the 24th, with the star Spica to the left of the planet. Take a look, as Jupiter is well to the west by nightfall and is slowly disappearing from the evening. Saturn partly makes up for it by its evening presence low in the south above Antares in Scorpius. We need only then wait for Venus to rise an hour or so before dawn. Miss this one? There's another one coming on April 8, 2024.

And then there are the perpetual August meteors, the Perseids. The debris of Comet Swift-Tuttle will hit the Earth at a peak rate the morning of Saturday the 12th. Usually yielding 60-80 meteors per hour. Perspective effects make them seem to come out the constellation Perseus. The best place to look is overhead. Unfortunately, the show will be partially wiped out by the bright gibbous Moon.

Look practically overhead for two stars northwest of bright Vega that represent they eyes of Draco, the celestial Dragon, who wraps himself between the Big and Little Dippers.

STARS OF THE WEEK: EU and U DEL (EU and U Delphini.) The Roman letters tell us immediately that we are dealing with variable stars, the naming system odd and thus readily recognizable. The(usually) sixth magnitude (6.25 and 6.38, almost seventh) stars are separated by only a couple degrees along an east-west line roughly 20 and 3/4 degrees north of the celestial equator in the ancient constellation Delphinus (the Dolphin) in the heart of the Milky Way. Oddly, both are semi-regular "SRb" semiregular red giant class M variables (respectively M6 and M5) with periods of 60 and 110 days and listed apparent magnitudes of 6.25 and 6.38. There seems to be no or little interstellar dimming, so we'll ignore it. With temperatures of 3300 and 3330 Kelvin and distances of 380 and 1570 light years (give or take 22 and 540), the luminosities are 600 and 8200 Suns. (For unknown reasons, the literature gives a luminosity for EU Del that is almost three times as high.) On the visual magnitude scale, in spite of its listed magnitude, EU Del flips between magnitudes 5.84 and 6.9, while U Delphini goes between 5.8 and 6.9 (the latter on a photographic scale, which makes red stars look fainter). EU's radius is calculated to be only 15 times that if the Sun, but the luminosity is suspect. The radius of EU is calculated at 420 solar radii, while interferometer measures give 275 in the infrared part of the spectrum). In spite of their generic name, SRb's are quite regular (whereas the semiregulars among supergiants (the SRc stars) are not). SRb's are thought to be stars in beginning stages of the collapse of the carbon core, which has now run out of helium fuel, and as they age and brighten will eventually become Long Period (Mira) variables. U is moving along at a marginally rapid 37 kilometers per second relative to the Sun. EU, however it is going much faster, at 77 km/s, which may be related to a high metallicity, the star coming from a different part of the Galaxy. The most interesting part of the story is that the variability periods are is 50.5 days for EU and 110 days for U, which bracket a seeming 60-day period, longer than which the stellar wind and mass loss increase as the stars eventually lose all their outer envelopes, the carbon/oxygen cores becoming white dwarfs. Most of the dust in the Milky Way comes from stars like these and their Long-Period" successors as they whittle themselves away, U Del losing mass at a rate of a million times that of the Sun In the solar wind).


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