Archive for March, 2016

The Sky This Week, March 30th thru April 5, 2016 !

The Sky This Week, 2016 March 30 – April 5

Lions and Archers and Bears, oh, my!
Jupiter, imaged on 2016 March 30 at 02:45 and 02:53.5 UT
imaged with the USNO 30.5-cm f/15 Clark/Saegmüller refractor

The Moon skirts the southern horizon in the morning sky this week, moving from the bright star clouds of the summer Milky Way into the sparse star fields of the rising autumnal constellations. Last Quarter occurs on March 31st at 11:17 am Eastern daylight Time. Luna may be found just to the north of the “Teapot” asterism in the constellation of Sagittarius, the Archer, a star pattern that we’ll see in the evening sky by late summer.

This week marks the April campaign for skywatchers who wish to participate in the Globe at Night citizen-science program that runs from now through April 8th. This month our focus constellation shifts from Orion to Leo, the Lion, which is well-placed for viewing just east of the meridian at the end of evening twilight. Leo is currently hosting the bright planet Jupiter which should help you locate it easily. Leo consists of two distinct asterisms, the “sickle” and the “Triangle”. To locate the Sickle, look to the northwest of Jupiter for the first-magnitude star Regulus. Moving up from the star you’ll see a semicircle of fainter stars that make up the Sickle’s blade. If you have a small telescope be sure to look at the brightest star in the blade, second-magnitude Algeiba. This is a fine double star consisting of two gold-tinted suns separated by about five arcseconds. Use a power of about 100X to split this excellent pair. The Triangle lies almost directly above Jupiter and consists of two third-magnitude stars and the second-magnitude star Denebola. To participate in the Globe at Night star count, go to the program’s website and compare your views of Leo with the provided finder charts. The brightness of your local sky is then determined by the number of stars that you see in Leo’s vicinity. It’s an easy observation to make, and your efforts will be incorporated into a global sky-brightness database.

If you look above Leo to the northern sky you should have no trouble finding the seven stars of the “Big Dipper”, an asterism made up of the brightest stars in the constellation of Ursa Major. There’s another easy double star here for the small telescope owner as well as a test for your naked-eye acuity. If you look at the star Mizar, which lies at the “bend” of the Dipper’s handle, you may see a fainter star butted up next to Mizar itself. This is Alcor, and it has been used as a test of visual sharpness for millennia. Point a telescope at this duo and you’ll see that Mizar itself is also double. This was the first non-planetary target I observed with my small 2.4-inch refractor back in 1960!

The showpiece for the evening is the giant planet Jupiter, which is now well up in the east as evening twilight fades. Old Jove is now about a month past opposition and is well-placed for prime-time viewing. You can see the planet and his four bright Galilean moons with almost any telescope; if you can hold a pair of binoculars steady enough you can just make them out as well. A three-inch telescope should show the planet’s two dark equatorial cloud belts, and each increase in aperture will bring out more detail. A six- to eight-inch telescope should begin to resolve the moons into tiny discs, and careful scrutiny at higher magnifications will show individual storms, swirls, and dark spots in the planet’s streaky cloud belts. From the eastern U.S. you can watch the moon Io drag its shadow across Jupiter’s face on the evening of the 30th, and on the evening of April 3rd the famous Great Red Spot rotates across the field of view.

Mars and Saturn continue to be best placed for viewing in the pre-dawn sky. Mars now rises in the southeast at local midnight, with Saturn following an hour later. The two planets continue to form a compact triangle with the bright red-tinted star Antares in the constellation of Scorpius, with Mars the brightest of the three objects. You’ll need a very calm morning to get a good telescopic view of these planets since their far southerly declination means we’re looking through lots of Earth’s turbulent atmosphere to spy details on their distant surfaces.


The Sky This Week, March 15 – 23, 2016 !

The Sky This Week, 2016 March 15 – 23

The equinox and the calendar.
Jupiter, imaged on 2016 March 9 at 02:45 UT

The Moon brightens the evening sky this week, waxing from First Quarter Full Moon, which occurs on the 23rd at 8:01 am Eastern Daylight Time. The Full Moon of March is popularly known as the Worm Moon, Crow Moon, Sap Moon, or Lenten Moon. This year it is a very important one for believers of Christianity. Since it is the first Full Moon that follows the vernal equinox it fixes the date of Easter, the most important of the moveable feasts in the Christian calendar. Luna starts the week high above the stars of Orion, then wends her way eastward through Gemini and Cancer. You’ll find her just under five degrees southeast of the bright star Regulus on the evening of the 20th. On the following night she cozies up to bright Jupiter, passing just two degrees south of the bright planet.

The vernal equinox occurs on the 20th at 12:30 am EDT. This is the moment when the Sun’s ecliptic longitude reaches zero degrees. For many ancient cultures this moment marked the beginning of a new year, and its date still figures prominently in the calendars of many religions. As mentioned before, it fixes the date of Easter for most of the world’s Christians, and it was the computation of this important date that led to the civil calendar that is almost universally observed today. The Gregorian Reform of 1582 was instituted by Pope Gregory XIII to correct errors in the Julian Calendar and the “Computus”, the formula used to calculate the date of Easter. By Gregory’s time the observed date of the equinox had slipped to March 11 in the Julian system, a full 10 days before the ecclesiastical equinox that was defined as March 21. Gregory’s reformers changed the formula for reckoning leap years, changing the Julian formula from a leap year every four calendar years to one in which there were 97 leap years in a 400 year cycle. Next, they removed 10 days from the calendar in October, 1582 to bring the astronomical vernal equinox back in synch with the ecclesiastical date of March 21. The Gregorian Calendar is not quite perfect, though, exceeding the true astronomical year by about 11 seconds. This error slowly accumulates, so equinoxes are gradually occurring a bit before the defined date of March 21. However, the date of the equinox won’t slip by a full day until somewhere around the year 3000.

In addition to the equinox, another sign of spring is now appearing in the east. By 10:00 pm EDT you may notice a bright star appearing above the eastern horizon. This is Arcturus, the brightest star in the northern hemisphere sky and the fourth-brightest of all the stars. The star’s rosy tint contrasts nicely with the cooler blue tints of the bright stars of winter found in Orion and Canis Major. It is one of the closer stars to the solar system, located at around 37 light-years from the Sun.

Thanks to Daylight Time, Jupiter gets a little bit more time to shine in the evening sky. The giant planet spends most of the night above the horizon, transiting the meridian after midnight. This should give you plenty of time to have a long look at this distant world that shows the largest apparent planetary disc to Earth-based telescopes. Virtually any optical aid will show the planet and his four bright moons first described by Galileo in 1610. As you increase the aperture of your telescope, more detail becomes apparent. In my four-inch refractor the planet’s prominent equatorial cloud belts are easily seen, and careful examination reveals swirls and spots within them as well as fainter parallel bands. An 8-inch telescope will show a great amount of fine-structure detail on nights of steady air, and the Galilean moons show discs and distinctive tints that reveal their identities. If you look at Old Jove on the evening of the 17th, you’ll have an excellent chance to see his most famous feature, the Great Red Spot, rotate across the disc.

Mars and Saturn may be found near the meridian in the pre-dawn hours. At 6:00 am they are both ideally placed for viewing through the telescope. Mars shows a gradually growing pink-tinted disc rimmed by a prominent white polar cap. Saturn looks like…well, Saturn. The planet’s distinctive rings are tipped about as much as they can get along our line of sight. Both planets will form an attractive triangle with the bright reddish star Antares for the next several weeks.

The Sky This Week, March 8 – 15, 2016 !

The Sky This Week, 2016 March 8 – 15

Springing forward in time.
Messier 42, the Great Nebula in Orion, imaged on 2016 March 7
under urban skies with a 10.2-cm (4-inch) f/6.5 refractor
and a Canon EOS Rebel T2i DSLR camera

The Moon returns to the evening sky this week, waxing to First Quarter on the 15th at 1:03 pm Eastern Daylight Time. She joins the stars of the Great Winter Circle by the week’s end. Look for Luna south of the Pleiades star cluster on the evening of the 13th. She may be found just east of the bright star Aldebaran on the following evening.

Yes, I slipped the word “daylight” into the time of the First Quarter Moon. This is the weekend when we set our clocks one hour ahead as we “spring forward” for Daylight Time. This annual ritual affects everyone in the country except for residents of Arizona and Hawai’i. In Hawai’i’s case it’s because the state is located in the tropics where the annual excursion of day/night change is relatively small. Arizona is excepted because the residents there never adopted Daylight Time when it was regulated by state statutes. The Federal law governing time zones and Daylight Time rule wasn’t codified until 1966; Arizona and certain western counties in Indiana were excepted. Since then the law has been modified twice, with the most recent bill passing Congress in 2005. Under this act all of Indiana now observes Daylight Time, but Arizona still stays on Mountain Standard Time. Whether you like Daylight Time or not, the U.S. Naval Observatory has nothing to do with it. Regulations regarding enforcement of standard time laws falls under the purview of the Department of Transportation. We provide the time-scale on which civil time is based, but we don’t tell you what to do with it! So, as a friendly reminder, Daylight Time officially begins at 2:00 am on Sunday morning, March 13th. Be sure to set your clocks ahead one hour and maintain that offset until November 6th, when we “fall back”.

The early evening hours are still dominated by the bright stars of the Great Winter Circle, but at this time of the year those stars seem to speed toward the western horizon at a fast pace. This is due to the fact that all stars transit the meridian four minutes earlier every night and that at this time of the year the length of daylight is increasing at its fastest rate. Later sunsets mean later twilight times, which cut into the time that the winter stars are visible in relative darkness. You still have time to enjoy the sights of Orion and his environs, but if you wait much longer you’ll find them wallowing in the west.

Jupiter now rises just before sunset, and by the time evening twilight deepens the sky to a dark blue you’ll find him shining brightly in the east. The giant planet is now in the prime-time of his current opposition, a tempting target for telescopes of all sizes. For the urban stargazer this is a great week for casual observing, with the Moon and Jupiter offering contrasting views. The barren cratered surface of Luna is the antithesis of the cloud-shrouded atmosphere of Jupiter. You’ll also notice that the entire apparent disc of Old Jove is about the same size as a modest lunar crater. However, the vast difference in distance between the two explains why an object the size of our Moon would appear as a tiny spot at the distance of Jupiter. What amazes me is that we can see features this small across the gulf of over 400 million miles in modest earthbound telescopes.

Mars rises at around midnight as the week opens, then gets thrown back by an hour as we shift to Daylight Time. The best time to see him is still before sunrise, and starting on the 13th you won’t have to get up super-early to see him. He is becoming brighter with each passing week as he marches eastward against the stars. This week he closes in on the second-magnitude star Graffias, northernmost star in the “head” of Scorpius. You’ll find the two objects very close together on the morning of the 16th.

You’ll find Saturn some 13 degrees east of Mars this week, shining at about the same brightness but with a yellowish hue. They are close to the meridian about an hour before sunrise and form an attractive triangle with the bright star Antares, the brightest luminary in Scorpius.

The Sky This Week, March 1 – 8, 2016 !

The Sky This Week, 2016 March 1 – 8

The night’s bright lights, some good, some bad.
Jupiter & three moons (plus a shadow), 2016 March 1, 03:44 UT

The Moon skims the southern horizon in the pre-dawn sky this week, passing through the rising constellations of summer and early autumn. New Moon occurs on March 8th at 8:54 pm Eastern Standard Time. Look for Luna to the northeast of Saturn before sunrise on the 2nd. If you have a flat southeastern horizon and a clear sky try to find the slender waning crescent Moon just three degrees to the north of dazzling Venus.

The March campaign for the Globe at Night citizen-science project gets underway on the 1st and runs through the 10th. This project is designed to involve interested people in the measurement and documentation of sky brightness from all over the world. The data collected by volunteer observers will be analyzed to determine the spread of light pollution, which is becoming an environmental issue that not only affects our view of the night sky but also some of the most basic rhythms in Nature. We now know that bright lights illuminating the sky affect migratory birds and sea turtles, and a growing body of evidence is finding links to a number of human conditions as well. Brightening skies also tell us something about our rampant consumption of energy resources. Your participation in this study is quite simple; just go out and see how many stars you can see in the constellation of Orion. You can submit your results via the project’s web page, or download star-measuring apps for your smart phone that will take your measurements and submit them “on the fly”. From dark locations well away from the city you should be able to see more than 30 stars within The Hunter’s bounds; urban observers may see no more than eight. Whatever result you get, it’s an important data point. You’re encouraged to submit many observations from different locations throughout the year. This is a great time to start, since Orion is one of the easiest constellations to identify.

A sure sign of impending spring is seeing Orion just west of the meridian at the end of evening twilight. You’ll find the rest of the bright stars of the Great Winter Circle well placed at 8:00 pm, with the gold-hued Capella dominating the view near the zenith and the blue-white glow of Sirius to the south. Sirius is the brightest star in the sky due to its relative proximity to the solar system and its intrinsic brightness. It shines with a luminosity some 25 times that of the Sun and lies just 8.6 light years away from us. To the ancient Egyptians the star represented Thoth, the god of wisdom and writing, and its first appearance just before sunrise anchored the Egyptian calendar. From our latitude Sirius never gets higher than about 35 degrees above the horizon, so its apparent “twinkling” is a good indicator of the stability of the atmosphere. If its light is steady it is a good night to drag the telescope out to view fine details on the Moon and planets; if it jumps around and flickers through the colors of the spectrum leave the telescope inside and enjoy the view with the naked eye or through binoculars.

Giant Jupiter reaches opposition on the morning of the 8th. For the nights immediately surrounding the date Old Jove will rise at sunset and set at sunrise. You’ll see him in the east at the end of evening twilight, and he’ll cross the meridian close to local midnight. At this time we’ll be at our closest to the giant planet at a distance of 664 million kilometers (412 million miles). When you look at Jupiter you’re actually seeing it as it was more than 36 minutes ago due to the finite speed of light! This is the best time to view Jupiter through the telescope with his disc presenting its largest apparent size toward us. On the night of the 7th you can watch the moons Io and Europa cross the planet’s disc accompanied by their shadows; after they emerge from the disc the Great Red Spot rotates into view.

Mars continues to slide eastward along the ecliptic, closing the gap with the star Graffias in the “head” of Scorpius. You’ll find the red planet near the meridian as morning twilight begins to brighten the sky. Mars is now a full magnitude brighter than his nearby stellar rival Antares. Through the telescope his disc is now twice the size it was back in January, but it is still quite small compared to Jupiter. Nonetheless, if you have a modest telescope and steady air you should be able to glimpse his north polar ice cap and the dark wedge of his most prominent surface feature, the Syrtis Major.

Saturn follows close on Mars’ heels. The ringed planet is just east of the meridian at the onset of morning twilight. By the week’s end he’ll form an attractive triangle with ruddy companions Antares and Mars. His rings are tipped very favorably to our line of sight and can be enjoyed with almost any telescope.