SKYLIGHTS

Skylights featured on Astronomy Picture of the Day

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Skylights featured nine times on Earth Science Picture of the Day: 1 2 3 4 5 6 7 8 9

Esquelpallasite

Photo of the Week.The Esquel (Argentina) pallasite is a stony iron meteorite with large mineral crystals. It probably came from the mantle-core boundary of a smashed up asteroid. A piece of the Sikhote-Alin iron is at the far right. (From the Goose Kaler memorial meteorite collection at Staerkel Planetarium).


Astronomy news for the week starting Friday, April 11, 2014.

Phone: (217) 333-8789
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.

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

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.


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

SSNEWEST! FIRST MAGNITUDE: A Book of the Bright Sky, World Scientific, 2013. Read the interview with Jim Kaler.


NEW! Read The Harp in Stellar Stories.




The next Skylights will appear Saturday, April 19.

A busy week lies ahead (or lay behind, depending on when you read this). The Moon starts off in the waxing gibbous phase as it grows to full the night of Monday, April 14 (really the morning of Tuesday the 15th), when it will undergo a fine total eclipse that's visible throughout almost all of North America plus western South America (but not in Europe). It then rather anticlimactically spends the remainder of the week in the waning gibbous phase, which is terminated at third quarter next week, on Monday the 21st. The evening of Sunday the 13th finds the Moon to the west of Mars . By the following night, it will have flipped to the other side. The morning of the eclipse the darkened Moon will be in a lovely setting just to the northeast of Spica, with Mars to the west. The morning of Wednesday the 16th, the waning Moon goes just south of Saturn.

The heart of the eclipse begins at 12:58 AM CDT the morning of Tuesday, April 15, when the full umbral shadow of the Earth takes its first bite out of the leading (eastern) edge of the lunar disk. The partial phase ends when the Moon enters totality at 2:07 AM, which maximizes at 2:46 AM with the northern edge of the Moon just missing the central core of the shadow. The Moon starts to leave full shadow, when it gets the first glimpse of sunlight, at 3:25 AM, and then completely leaves the full shadow behind at 4:33 AM, not long before moonset. Add an hour for Eastern Daylight Time, subtract one for MDT, two for PDT, three for Alaska, and five for Hawaii. Even in totality, though quite dark and red, the Moon is visible as a result of sunlight scattered and refracted by the Earth's atmosphere into the umbral shadow. The degree of darkness depends on the state of the Earth's atmospheric blanket, particularly on recent volcanic action that makes it more opaque. Since the Moon passes just south of the central shadow, the northern limb of the Moon will be the darkest at mid-eclipse. The penumbral stages, where the Moon is in just partial earth shadow, are not much worth bothering with, though the effect can be seen as a slight dimming just before and after the main eclipse.

In addition to the eclipse, we get to admire a fine array of planets. First up is Jupiter, which has already entered the high western sky by the time the sky is dark, and is with us until 2 AM. By midnight, reddish Mars, making a fine color contrast with Spica to the southeast, has also crossed the southern divide. Just past opposition to the Sun, the planet's motion is obvious over only a few nights. It makes its closest approach to the Earth (0.62 Astronomical Units, 93 kilometers, 58 million miles) for this orbital round on Monday the 14th. Next is Saturn, which rises just past the end of evening twilight and crosses to the south around 3 AM. Finally, just before dawn, Venus rises in the east and takes over the sky, not fading away in the until bright morning twilight.

If that is not enough, Venus passes less than a degree north of Neptune on Saturday the 12th, Vesta (the brightest asteroid) and Ceres (at 470 km, 290 miles, the largest) both go through opposition to the Sun (respectively on Sunday the 13th and Tuesday the 15th), and Pluto begins retrograde motion on Monday the 14th.

From Mars and Spica, look toward the north to the brightest star in the northern hemisphere, Arcturus, the Bear Driver, who follows Ursa Major around the northern pole. As Ursa Major's Big Dipper passes nearly overhead, the Little Dipper of Ursa Minor rises up to meet it.

STAR OF THE WEEK: 5 UMI (5 UrsaeMinoris). At fourth magnitude (4.25), number 5 in the Flamsteed list of numbered stars in Ursa Minor was obviously too faint for Bayer to make note of via Greek letter (though he and others indeed lettered fainter ones). Five Ursae Minoris may also be among the more prominent stars that everybody with a dark sky sees but pays no attention to. It's supremely easy to find and, given its position of only 14 degrees from the North Celestial Pole, it's visible from nearly everywhere north of 14 degrees north latitude any time of night. The front bowl stars of the Big Dipper, Merak and Dubhe (Beta and Alpha UMa), are famed as the Pointers to Polaris, the North Star. Similarly, the front bowl stars of the Little Dipper, Pherkad and Kochab (Beta and Gamma UMi), point right to 5 UMi. Only it's a lot closer, just 2 degrees north-northeast of second magnitude Kochab. It's so close that it might make a good addition to the Little Dipper as a drop of water flying off its lip. Beyond that, the star is among the most common types in the visual bestiary, a class K (but cooler than normal, K4) giant (oddly the same as Kockab) 359 light years away (with a likely uncertainty of just 5 light years). The recorded temperatures have a large range, from 4070 to 4395 Kelvin, with an average of 4230, which somewhat compromises correction for infrared radiation. Using the average temperature, 5 UMi shines with the light of 413 Suns (with an uncertainty of perhaps 20 percent, really not all that bad). Temperature and luminosity then give a radius of 38 times that of the Sun, 0.18 Astronomical Units, roughly 60 percent the size of Mercury's orbit. Were it in our solar system, the orange star would glower nearly 20 degrees across, about the separation between Betelgeuse and Rigel. A low projected equatorial rotation speed of 1.9 kilometers per second indicates a rotation period that (were the rotation axis perpendicular to the line of sight) could be as long as 2.5 years. The theory of stellar structure and evolution give a mass perhaps as high as 4 times that of the Sun and show that the star is probably fusing its core helium to carbon and oxygen, though it could be just past that state as it makes ready to become an even bigger giant. The iron content is about three-fourths solar, nothing unusual, nor is the speed of motion relative to the Sun. At four solar masses, stars don't live very long; 5 UMi had a hydrogen-fusing lifetime of just 180 million years. After sloughing off its outer envelope, the core will turn into a white dwarf of just under 0.8 of a solar mass. At 59 and 23 seconds of arc away are thirteenth and tenth magnitude "companions" whose motions clearly show both to be just line-of-sight "optical" coincidences. Five UMi is, however, listed as a mild barium star, which suggests the vague possiblility that there is a white dwarf companion that as a swollen enriced giant contaminated the star we see now.


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