Sky This Week is brought to you in part by Celestron.
Friday, March 7
Look north after dark tonight to find the curved form of the Little Dipper. The smaller of the two famous dipper-shaped asterisms in the northern sky, the Little Dipper extends from the North Star, Polaris, at the end of its handle. But while this 2nd-magnitude star is famous for currently sitting at Earth’s North Celestial Pole, Polaris isn’t the only such sun to have this claim to fame.
Earth has a slight wobble as it spins, which over time causes the North Pole to shift, tracing out a large circle on the sky. As it does so, the star at the North Celestial Pole changes, and tonight we’ll visit the North Star of 5,000 years ago: Thuban.
Fainter than Polaris, magnitude 3.7 Thuban is also cataloged as Alpha (α) Draconis. To find it, follow the curve of the Little Dipper’s handle to its bowl. The two stars at the far end of the bowl are Kochab (Beta [β] Ursae Minoris) and Pherkad (Gamma [γ] UMi). Thuban lies just over 10° southwest of Pherkad, just over the border in Ursa Minor’s neighboring constellation, Draco. While the ancient Egyptian civilization flourished, Thuban served as their North Star.
Thuban is a few times the mass of our Sun and lies about 300 light-years away. It is several hundred times as bright as our star and either reaching the end of its hydrogen core-burning main sequence stage of life or perhaps has already slipped into the subgiant phase, which occurs shortly before it becomes a true red giant star.
Sunrise: 6:23 A.M.
Sunset: 5:59 P.M.
Moonrise: 11:11 A.M.
Moonset: 2:26 A.M.
Moon Phase: Waxing gibbous (62%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.
Saturday, March 8
High in the southeast in the two hours before sunrise is the large constellation Ophiuchus. The southern region of this star pattern is where we’re focusing our attention this morning to find the 8th-magnitude globular cluster M9.
One of the easiest ways to locate M9 is to start at magnitude 2.4 Eta (η) Ophiuchi and simply drop 3.5° southeast. Stretching about 12’ across, M9 is nearly half the width of the Full Moon — but in most amateur instruments, only the inner 3’ of its compact core is visible. In binoculars, it will look like a small, dim, nebulous smudge of light. With a telescope, you’ll see that it has a bright, compact center that dissolves into individual stars around the periphery, particularly at higher powers and with larger scopes.
M9 lies nearly 26,000 light-years away and is also moving at high velocity, appearing to recede from Earth at some 140 miles (224 kilometers) per second.
Sunrise: 6:22 A.M.
Sunset: 6:00 P.M.
Moonrise: 12:14 P.M.
Moonset: 3:24 A.M.
Moon Phase: Waxing gibbous (72%)
Sunday, March 9
Daylight saving time begins at 2 A.M. local time this morning. At that time, in locations where DST is observed clocks will “spring forward” to 3 A.M., skipping 2 A.M. altogether. As a result the Sun and Moon will rise and set an hour later today, with daylight now lingering longer into the evening hours.
Mercury passes 6° south of Venus at 7 A.M. EDT. Both planets are visible in the evening sky and now is the time to get in your last views, as they are getting lower each night and will soon be lost in twilight even as their phases also diminish.
Forty minutes after sunset, Mercury is still nearly 10° high in the west, with Venus to its upper right. The latter is far easiest to spot, blazing at magnitude –4.6. Mercury is fainter at magnitude –0.2, but still outshines the fainter stars in this region of the sky, which will slowly start to pop out as twilight fades. To both planets’ right is the setting Square of Pegasus, while above them is the small, faint constellation Aries. Above that is Taurus, which sports the red giant star Aldebaran and the famous Pleiades star cluster, as well as the bright planet Jupiter to Aldebaran’s upper right. We’ll be returning to this region in just a few days to catch a show put on by two of Jupiter’s Galilean moons.
For now, take a look at Mercury and Venus through a telescope. Mercury spans 8” and shows off a nearly 40-percent-lit crescent. Venus, meanwhile, is a hefty 55” across but is only barely illuminated, with just 7 percent of its cloud tops lit by the Sun.
Sunrise: 7:20 A.M.
Sunset: 7:01 P.M.
Moonrise: 2:22 P.M.
Moonset: 5:10 A.M.
Moon Phase: Waxing gibbous (80%)
Monday, March 10
Early evening is a great time to spot a colorful double star in Cassiopeia, which is sits to the left of the Little Dipper in the evening sky at this time of year. Look for the Queen’s familiar W shape in the northern sky, currently on its side and looking a bit like the letter E around 9 P.M. local daylight time this evening.
We are looking for Eta Cassiopeiae (also called Achird), a magnitude 3.5 star that sits 1.7° northeast (to the upper right) of brighter, 2nd-magnitude Shedar (Alpha Cas). Eta Cas consists of two stars some 13” apart, meaning they can be split by virtually any instrument, from binoculars to any size telescope. Lower power works best to see the stars’ differing colors: a yellow-gold magnitude 3.4 primary beside a ruby-red magnitude 7.5 secondary. Under higher power, the pair often looks white and yellow instead, according to Astronomy associate editor Michael Bakich.
Sunrise: 7:19 A.M.
Sunset: 7:02 P.M.
Moonrise: 3:31 P.M.
Moonset: 5:47 A.M.
Moon Phase: Waxing gibbous (88%)
Tuesday, March 11
Those willing to stay up late can watch as not one but two shadows cross the disk of Jupiter. Thanks to their current alignment, both Europa and Ganymede pass in front of Jupiter tonight, and for a while both of their shadows are visible on the gas giant’s cloud tops at the same time.
Locating Jupiter is easy — it’s the brightest point of light in Taurus the Bull, still high in the southwest after sunset. Observers in the eastern half of the U.S. will see Europa transiting the disk as darkness falls, with Ganymede just off the planet’s southwestern limb. Europa is moving from east to west, heading toward the western limb as Ganymede continues to pull away in the same direction. Around 10:15 P.M. EDT, Europa’s shadow appears on the southeastern limb, just as the moon itself is slipping away from the disk on the opposite side.
Wait half an hour and another shadow appears, larger and to the southeast of Europa’s shadow — this is Ganymede’s shadow, trailing farther behind the larger moon thanks to its wider orbit. The two shadows cross the disk together between about 11 P.M. and 12:45 A.M. EDT (now early on the 12th in the Eastern time zone), when Europa’s shadow starts to leave the disk first. Within 20 minutes, Ganymede’s shadow begins to disappear as well.
Sunrise: 7:18 A.M.
Sunset: 7:03 P.M.
Moonrise: 4:37 P.M.
Moonset: 6:16 A.M.
Moon Phase: Waxing gibbous (94%)
Wednesday, March 12
Saturn is in conjunction with the Sun at 6 A.M. EDT. Twelve hours later, asteroid 8 Flora reaches opposition in Leo the Lion at 6 P.M. EDT. However, with a bright Moon nearby, it will be difficult to catch sight of the faint main-belt world.
We’ll instead aim for a brighter target on the other side of the sky: 5th-magnitude M35 in Gemini. This open cluster is located near the Twins’ feet, in the northwestern portion of the constellation. The easiest way to find it is simply to hop 2.3° northwest of magnitude 3.3 Eta Geminorum.
Shining at magnitude 5.3, M35 spans about 28’, making it nearly as large as the Full Moon. It’s a great binocular object and shows up best in small scopes under low magnification and with larger fields of view. You can even try using your telescope’s finder scope to enjoy this rich group of young stars.
Observers with larger scopes can challenge themselves to find NGC 2158, a much more compact 9th-magnitude cluster just 15’ southwest of M35. NGC 2158 is about six times smaller than M35, with its stars packed much closer together. It is also much older and several times more distant than M35, which lies only about 3,000 light-years away.
Sunrise: 7:16 A.M.
Sunset: 7:04 P.M.
Moonrise: 5:42 P.M.
Moonset: 6:41 A.M.
Moon Phase: Waxing gibbous (98%)
Thursday, March 13
Mercury & Venus appear side by side tonight in the evening sky. The two planets are 5.5° apart and remain visible for more than an hour after sunset. You’ll need to wait a little while after the Sun disappears to see them both, as Mercury is now magnitude 0.5 and will take some time to appear to the left of Venus as twilight deepens. By contrast, Venus will be easy to spot earlier on, still a bright magnitude –4.4.
The pair is 7° high in the west 40 minutes after sunset. Pull out your telescope and compare their appearance with what you saw earlier this week. Both have changed quite a bit. Venus is now 57” wide but only 4 percent lit. Mercury has grown slightly to 9” wide and is now 22 percent lit.
The real showstopper tonight is a total lunar eclipse, which begins late this evening and continues overnight into the early-morning hours of March 14. Everyone across the U.S. will be able to view the Moon changing color as it moves through Earth’s shadow. Moonrise occurs shortly before sunset, with the Moon hanging in southeastern Leo near that constellation’s border with Virgo. Luna is essentially Full, with our satellite officially reaching 100 percent lit early tomorrow morning, around the time of mid-eclipse.
The first phase of the eclipse — called the penumbral phase, when the Moon first starts to pass into the outer regions of Earth’s shadow — begins just shy of midnight in the Eastern time zone, at 11:57 P.M. EDT. Most observers won’t notice much change on the face of the Moon at this time. The real transformation will start once the Moon passes into the darker, more central part of Earth’s shadow just before 1:10 A.M. EDT, now early on March 14 for the eastern half of the country. This is when the visible disk of the Moon will start to darken and slowly change color, as sunlight is scattered through Earth’s atmosphere and falls onto the Moon.
Keep reading as we follow the eclipse’s progression into the early-morning hours of the 14th, below.
Sunrise: 7:14 A.M.
Sunset: 7:05 P.M.
Moonrise: 6:44 P.M.
Moonset: 7:03 A.M.
Moon Phase: Full
Friday, March 14
March 14 begins with a total lunar eclipse underway across the U.S. No special equipment is needed to watch it — in fact, your eyes are the best tools you have to enjoy such an event.
Totality begins at 2:26 A.M. EDT. This is shortly before Full Moon occurs at 2:55 A.M. EDT, which is also just moments before greatest eclipse at 2:59 A.M. EDT. This is the moment when the Moon is centrally located within the darkest part of Earth’s shadow.
Pay special attention to the Moon’s color, as no two eclipses appear exactly the same. That color is influenced by the state of Earth’s atmosphere, including the amount and type of particulates in the air. You can use the illustration below to rank the Moon’s brightness and color at mid-eclipse.
Totality ends just after 3:31 A.M. EDT. Then the eclipse plays out in reverse, with the Moon growing lighter as it moves out of the central portions of Earth’s shadow. The partial phase ends just before 4:48 A.M. EDT, and the Moon passes fully out of the lighter portion of Earth’s shadow — ending the eclipse — at 6 A.M. EDT, roughly an hour before sunrise.
Mercury reaches its stationary point at 5 P.M. EDT this evening. We’ll revisit the solar system’s smallest planet next week, so stay tuned for more details.
Sunrise: 7:13 A.M.
Sunset: 7:06 P.M.
Moonrise: 7:44 P.M.
Moonset: 7:23 A.M.
Moon Phase: Full
