Stalking the Lunar X

This week offers observers a shot at capturing a fascinating but elusive lunar feature.

But why study the Moon? It’s a question we occasionally receive as a backyard astronomer. There’s a sort of “been there, done that” mentality associated with our nearest natural neighbor in space. Keeping one face perpetually turned Earthward, the Moon goes through its 29.5 synodic period of phases looking roughly the same from one lunation to the next. Then there’s the issue of light pollution. Many deep sky imagers “pack it in” during the weeks surrounding the Full Moon, carefully stacking and processing images of wispy nebulae and dreaming of darker times ahead…

But fans of the Moon know better. Just think of life without the Moon. No eclipses. No nearby object in space to give greats such as Sir Isaac Newton insight into celestial mechanics 101. In fact, there’s a fair amount of evidence to suggest that life arose here in part because of our large Moon. The Moon stabilizes our rotational axis and produces a large tidal force on our planet. And as all students of lunar astronomy know, not all lunations are exactly equal.

A daytime capture of the Lunar X. (Photo by Author).
A daytime capture of the Lunar X. (Photo by Author).

This week, we get a unique look at a feature embedded in the lunar highlands which demonstrates this fact. The Lunar X, also sometimes known as the Purbach cross or the Werner X reaches a decent apparition on March 19th at 11:40UT/7:40EDT favoring East Asia and Australia. This feature is actually the overlapping convergence of the rims of Blanchinus, La Caille and Purbach craters. The X-shaped feature reaches a favorable illumination about six hours before 1st Quarter phase and six hours after Last Quarter phase. It is pure magic watching the X catch the first rays of sunlight while the floor of the craters are still immersed in darkness. For about the span of an hour, the silver-white X will appear to float just beyond the lunar terminator.

Visibility of the Lunar X for the Remainder of 2013.

Lunation Date Time Phase Favors
1116 March 19th 11:40UT/7:40EDT Waxing East Asia/Australia
1116 April 3rd 3:20UT/23:20EDT* Waning Africa/Europe
1117 April 17th 23:47UT/19:47EDT Waxing Eastern North America
1117 May 2nd 16:19UT/12:19EDT Waning Central Pacific
1118 May 17th 10:51UT/6:51EDT Waxing East Asia/Australia
1118 June 1st 4:31UT/0:31EDT Waning Western Africa
1119 June 15th 21:21UT/17:21EDT Waxing South America
1119 June 30th 16:04UT/12:04EDT Waning Western Pacific
1120 July 15th 7:49UT/3:49EDT Waxing Australia
1120 July 30th 3:16UT/23:16EDT* Waning Africa/Western Europe
1121 August 13th 18:50UT/14:50EDT Waxing South Atlantic
1121 August 28th 14:27UT/10:27EDT Waning Central Pacific
1122 September 12th 9:50UT/5:50EDT Waxing East Asia/Australia
1122 September 27th 2:00UT/22:00EDT* Waning Middle East/East Africa
1123 October 11th 19:52UT/15:52EDT Waxing Atlantic Ocean
1123 October 26th 14:12UT/10:12EDT Waning Central Pacific
1124 November 10th 10:03UT/5:03EST Waxing East Asia/Australia
1124 November 25th 3:14UT/22:14EST* Waning Africa/Europe
1125 December 10th 00:57UT/19:57EST Waxing Western North America
1126 December 24th 17:07UT/12:07EST Waning Western Pacific
*Times marked in bold denote visibility in EDT/EST the evening prior.


Fun Factoid: All lunar apogees and perigees are not created equal either. The Moon also reaches another notable point tonight at 11:13PM EDT/ 3:13 UT as it arrives at its closest apogee (think “nearest far point”) in its elliptical orbit for 2013 at 404,261 kilometres distant. Lunar apogee varies from 404,000 to 406,700 kilometres, and the angular diameter of the Moon appears 29.3’ near apogee versus 34.1’ near perigee. The farthest and visually smallest Full Moon of 2013 occurs on December 17th.

The first sighting of the Lunar X feature remains a mystery, although modern descriptions of the curious feature date back to an observation made by Bill Busler in June 1974. As the Sun rises across the lunar highlands the feature loses contrast. By the time the Moon reaches Full, evidence of the Lunar X vanishes all together. With such a narrow window to catch the feature, many longitudes tend to miss out during successive lunations. Note that it is possible to catch the 1st and Last Quarter Moon in the daytime.

A 1st Quarter Moon with the Lunar X (inset). (Photo by Author).
A 1st Quarter Moon with the Lunar X (inset). (Photo by Author).

Compounding the dilemma is the fact that the lighting angle for each lunation isn’t precisely the same. This is primarily because of two rocking motions of the Moon known as libration and nutation. Due to these effects, we actually see 59% of the lunar surface. We had to wait for the advent of the Space Age and the flight of the Soviet spacecraft Luna 3 in 1959 to pass the Moon and look back and image its far side for the first time.

We actually managed to grab the Lunar X during a recent Virtual Star Party this past February. Note that another fine example of lunar pareidolia lies along the terminator roughly at the same time as the Lunar X approaches favorable illumination. The Lunar V sits near the center of the lunar disk near 1st and Last Quarter as well and is visible right around the same time. Formed by the confluence of two distinct ridges situated between the Mare Vaporum and Sinus Medii, it is possible to image both the Lunar X and the Lunar V simultaneously!

A simultaneous capture of the Lunar X & the Lunar V features. (Photo by Author).
A simultaneous capture of the Lunar X & the Lunar V features. (Photo by Author).

This also brings up the interesting possibility of more “Lunar letters” awaiting discovery by keen-eyed amateur observers… could a visual “Lunar alphabet be constructed similar to the one built by Galaxy Zoo using galactic structures? Obviously, the Moon has no shortage of “O’s,” but perhaps “R” and “Q” would be a bit more problematic. Let us know what you see!

-Thanks to Ed Kotapish for providing us with the calculations for the visibility of the Lunar X for 2013.


Weekly SkyWatcher’s Forecast: September 24-30, 2012

“Shine on, shine on Harvest Moon… Up in the sky…” Oh! Howdy, fellow SkyWatchers! The seasons are most surely showing their changes in both hemispheres and this week marks the famous “Harvest Moon”. The Moon will very much be in the eyepiece this week, so enjoy some great studies. However, don’t put away your telescopes just yet! Bright skies are a great time to catch up on double star studies and variables. Whenever you’re ready, just meet me in the back yard…

Monday, September 24 – In 1970, the first unmanned, automated return of lunar material to the Earth occurred on this day when the Soviet’s Luna 16 returned with three ounces of the Moon. Its landing site was eastern Mare Fecunditatis. Look just west of the bright patch of Langrenus. Let’s walk upon the Moon this evening as we take a look at sunrise over one of the most often studied and mysterious of all craters – Plato. Located on the northern edge of Mare Imbrium and spanning 95 kilometers in diameter, Class IV Plato is simply a feature that all lunar observers check because of the many reports of unusual happenings. Over the years, mists, flashes of light, areas of brightness and darkness, and the appearance of small craters have become a part of Plato’s lore.

On October 9, 1945 an observer sketched and reported “a minute, but brilliant flash of light” inside the western rim. Lunar Orbiter 4 photos later showed where a new impact may have occurred. While Plato’s interior craterlets average between less than one and up to slightly more than two kilometers in diameter, many times they can be observed – and sometimes they cannot be seen at all under almost identical lighting conditions. No matter how many times you observe this crater, it is ever changing and very worthy of your attention!

Although tonight’s bright skies will make our next target a little difficult to find visually, look around four fingerwidths southwest of Delta Capricorni (RA 21 26 40 Dec -22 24 40) for Zeta. Also known as 34 Capricorni, Zeta is a unique binary system. Located about 398 light-years from Earth, the primary star is a yellow supergiant with some very unusual properties – it’s the warmest, most luminous barium star known. But that’s not all, because the B component is a white dwarf almost identical in size to our own Sun!

Tuesday, September 25 – Tonight would be a great opportunity to take another look at crater Eratosthenes. Just slightly north of lunar center, this easily spotted feature dangles at the end of the Apennine Mountain range like a yo-yo caught on a string. Its rugged walls and central peaks make for excellent viewing. If you look closely at the mountains northeast of Eratosthenes, you will see the high peak of Mons Wolff. Named for the Dutch philosopher and mathematician, this outstanding feature reaches 35 kilometers in height. To the southwest of Era-tosthenes you may also spot the ruined remains of crater Stadius. Very little is left of its walls and the floor is dotted with small strikes. Near the twin pair of punctuations to its south lie the remains of Surveyor 2! Now let’s journey to a very pretty star field as we head toward the western wing tip in Cygnus to have a look at Theta – also known as 13 Cygni. It is a beautiful main sequence star that is also considered by modern catalogs to be a double. For large telescopes, look for a faint (13th magnitude) companion to the west… But it’s also a wonderful optical triple!

Also in the field with Theta to the southeast is the Mira-type variable R Cygni, which ranges in magnitude from around 7 to 14 in slightly less than 430 days. This pulsating red star has a really quite interesting history that can be found at AAVSO, and is circumpolar for far northern observers. Check it out!

Wednesday, September 26 – Tonight on the Moon, let’s take an in-depth look at one of the most impressive of the southern lunar features – Clavius.

Although you cannot help but be drawn visually to this crater, let’s start at the southern limb near the terminator and work our way up. Your first sighting will be the large and shallow dual rings of Casatus with its central crater and Klaproth adjoining it. Further north is Blancanus with its series of very small interior craters, but wait until you see Clavius. Caught on the southeast wall is Rutherford with its central peak and crater Porter on the northeast wall. Look between them for the deep depression labeled D. West of D you will also see three outstanding impacts: C, N and J; while CB resides between D and Porter. The southern and southwest walls are also home to many impacts, and look carefully at the floor for many, many more! It has been often used as a test of a telescope’s resolving power to see just how many more craters you can find inside tremendous old Clavius. Power up and enjoy!

And if you’d like to visit an object that only requires eyes, then look no further than Eta Aquilae one fist-width due south of Altair…

Discovered by Pigot in 1784, this Cepheid-class variable has a precision rate of change of over a magnitude in a period of 7.17644 days. During this time it will reach of maximum of magnitude 3.7 and decline slowly over 5 days to a minimum of 4.5… Yet it only takes two days to brighten again! This period of expansion and contraction makes Eta very unique. To help gauge these changes, compare Eta to Beta on Altair’s same southeast side. When Eta is at maximum, they will be about equal in brightness.

Thursday, September 27 – Tonight exploring the Moon will be in order as one of the most graceful and recognizable lunar features will be prominent – Gassendi. As an ancient mountain-walled plain that sits proudly at the northern edge of Mare Humorum, Gassendi sports a bright ring and a triple central mountain peak that are within the range of binoculars.

Telescopic viewers will appreciate Gassendi at high power in order to see how its southern border has been eroded by lava flow. Also of note are the many rilles and ridges that exist inside the crater and the presence of the younger Gassendi A on the north wall. While viewing the Mare Humorum area, keep in mind that we are looking at an area about the size of the state of Arkansas. It is believed that a planetoid collision originally formed Mare Humorum. The incredible impact crushed the surface layers of the Moon resulting in a concentric “anticline” that can be traced out to twice the size of the original impact area. The floor of this huge crater then filled in with lava, and was once thought to have a greenish appearance but in recent years has more accurately been described as reddish. That’s one mighty big crater!

Tonight we’ll begin with an easy double star and make our way towards a more difficult one. Beautiful, bright and colorful, Beta Cygni is an excellent example of an easily split double star. As the second brightest star in the constellation of Cygnus, Albireo lies roughly in the center of the “Summer Triangle” making it a relatively simple target for even urban telescopes.

Albireo’s primary (or brightest) star is around magnitude 4 and has a striking orangish color. Its secondary (or B) star is slightly fainter at a bit less than magnitude 5, and often appears to most as blue, almost violet. The pair’s wide separation of 34? makes Beta Cygni an easy split for all telescopes at modest power, and even for larger binoculars. At approximately 410 light-years away, this colorful pair shows a visual separation of about 4400 AU, or around 660 billion kilometers. As Burnham noted, “It is worth contemplating, in any case, the fact that at least 55 solar systems could be lined up, edge-to-edge, across the space that separates the components of this famous double!”

Now let’s have a look at Delta. Located around 270 light-years away, Delta is known to be a more difficult binary star. Its duplicity was discovered by F. Struve in 1830, and it is a very tough test for smaller optics. Located no more than 220 AU away from the magnitude 3 parent star, the companion orbits anywhere from 300 to 540 years and is often rated as dim as 8th magnitude. If skies aren’t steady enough to split it tonight, try again! Both Beta and Delta are on many challenge lists.

Friday, September 28 – Tonight our primary lunar study is crater Kepler. Look for it as a bright point, slightly lunar north of center near the terminator. Its home is the Oceanus Procellarum – a sprawling dark mare composed primarily of dark minerals of low reflectivity (albedo) such as iron and magnesium. Bright, young Kepler will display a wonderfully developed ray system. The crater rim is very bright, consisting mostly of a pale rock called anorthosite. The “lines” extending from Kepler are fragments that were splashed out and flung across the lunar surface when the impact occurred. The region is also home to features known as “domes” – seen between the crater and the Carpathian Mountains. So unique is Kepler’s geological formation that it became the first crater mapped by U.S. Geological Survey in 1962.

Up next, we’ll have a look at the central star of the “Northern Cross” – Gamma Cygni. Also known as Sadr, this beautiful main sequence star lies at the northern edge of the “Great Rift.” Surrounded by a field of nebulosity known as IC 1310, second magnitude Gamma is very slowly approaching us, but still maintains an average distance of about 750 light-years. It is here in the rich, starry fields that the great dust cloud begins its stretch toward southern Centaurus – dividing the Milky Way into two streams. The dark region extending north of Gamma towards Deneb is often referred to as the “Northern Coalsack,” but its true designation is Lynds 906.

If you take a very close look at Sadr, you will find it has a well-separated 10th magnitude companion star, which is probably not related – yet in 1876, S. W. Burnham found that it itself is a very close double. Just to its north is NGC 6910 (Right Ascension: 20 : 23.1 – Declination: +40 : 47), a roughly 6th magnitude open cluster which displays a nice concentration in a small telescope. To the west is Collinder 419, another bright gathering that is nicely concentrated. South is Dolidze 43, a widely spaced group with two brighter stars on its southern perimeter. East is Dolidze 10, which is far richer in stars of various magnitudes and contains at least three binary systems.

Whether you use binoculars or telescopes, chances are you won’t see much nebulosity in this region – but the sheer population of stars and objects in this area makes a visit with Sadr worthy of your time!

Saturday, September 29 – Tonight we’re going to have a look at a lunar feature that goes beyond simply incredible – it’s downright weird. Start your journey by identifying Kepler and head due west across Oceanus Procellarum until you encounter the bright ring of crater Reiner. Spanning 30 kilometers, this crater isn’t anything in particular – just shallow-looking walls with a little hummock in the center. But, look further west and a little more north for an anomaly – Reiner Gamma.

Well, it’s bright. It’s slightly eye-shaped. But what exactly is it? Possessing no real elevation or depth above the lunar surface, Reiner Gamma could very well be an extremely young feature caused by a comet. Only three other such features exist – two on the lunar far side and one on Mercury. They are high albedo surface deposits with magnetic properties. Unlike a lunar ray of material ejected from below the surface, Reiner Gamma can be spotted during the daylight hours – when ray systems disappear. And, unlike other lunar formations, it never casts a shadow.

Reiner Gamma also causes a magnetic deviation on a barren world that has no magnetic field. This has many proposed origins, such as solar storms, volcanic gaseous activity, or even seismic waves. But, one of the best explanations for its presence is a cometary strike. It is believed that a split-nucleus comet, or cometary fragments, once impacted the area and the swirl of gases from the high velocity debris may have somehow changed the regolith. On the other hand, ejecta from an impact could have formed around a magnetic “hot spot,” much like a magnet attracts iron filings. No matter which theory is correct, the simple act of viewing Reiner Gamma and realizing that it is different from all other features on the Moon’s earthward facing side makes this journey worth the time!

When you’re done, let’s head about a fingerwidth south of Gamma Cygni to have a look at an open cluster well suited for all optics – M29 (Right Ascension: 20 : 23.9 – Declination: +38 : 3).

Discovered in 1764 by Charles Messier, this type D cluster has an overall brightness of about magnitude 7, but isn’t exactly rich in stars. Hanging out anywhere from 6000 to 7200 light-years away, one would assume this to be a very rich cluster and it may very well have hundreds of stars – but their light is blocked by a dust cloud a thousand times more dense than average. Approaching us at around 28 kilometers per second, this loose grouping could be as old as 10 million years and appears much like a miniature of the constellation of Ursa Major at low powers. Even though it isn’t the most spectacular in star-rich Cygnus, it is another Messier object to add to your list!

Sunday, September 30 – Today in 1880, Henry Draper must have been up very early indeed when he took the first photo of the Great Orion Nebula (M42). Although you might not wish to set up equipment before dawn, you can still use a pair of binoculars to view this awesome nebula! You’ll find Orion high in the southeast for the Northern Hemisphere, and M42 in the center of the “sword” that hangs below its bright “belt” of three stars.

Our seasons are changing – and so the seasons change on other planets, too. Today marks the universal date on which Northern Autumn, Southern Spring Equinox occurs on Mars. Keep an eye for subtle changes in surface features of the red planet!

This is also the Universal date the Moon will become Full and it will be the closest to the Autumnal Equinox. Because its orbit is more nearly parallel to the eastern horizon, it will rise at dusk for the next several nights in a row. On the average, the Moon rises about 50 minutes later each night, but at this time of year it’s around 20 minutes later for mid-northern latitudes and even less farther north. Because of this added light, the name “Harvest Moon” came about because it allowed farmers more time to work in the fields.

Often times we perceive the Harvest Moon as being more orange than at any other time of the year. The reason is not only scientific enough – but true. Coloration is caused by the scattering of the light by particles in our atmosphere. When the Moon is low, like now, we get more of that scattering effect and it truly does appear more orange. The very act of harvesting itself produces more dust and often times that coloration will last the whole night through. And we all know the size is only an “illusion”…

So, instead of cursing the Moon for hiding the deep sky gems tonight, enjoy it for what it is…a wonderful natural phenomenon that doesn’t even require a telescope!

Until next week? Ask for the Moon, but keep on reaching for the stars!

Weekly SkyWatcher’s Forecast: June 18-24, 2012

Greetings, fellow SkyWatchers! Let’s begin the week with some awesome galactic studies and enjoy a meteor shower during Summer Solstice! We’ll be studying variable stars, the planet Mars, Saturn, the Moon and Mercury, too! There’s always a bit of astronomy history and some unusual things to learn about. When you’re ready, just meet me in the back yard…

Monday, June 18 – With dark skies on our side, we’ll spend the next few days concentrating on a very specific region of the night sky. Legend tells us the constellation of Crater is the cup of the gods – cup befitting the god of the skies, Apollo. Who holds this cup, dressed in black? It’s the Raven, Corvus. The tale is a sad one – a story of a creature sent to fetch water for his master, only to tarry too long waiting on a fig to ripen. When he realized his mistake, the sorry Raven returned to Apollo with his cup and brought along the serpent Hydra in his claws as well. Angry, Apollo tossed them into the sky for all eternity and it is in the south they stay until this day.

For the next few days, it will be our pleasure to study the Cup and the Raven. The galaxies I have chosen are done particularly for those of us who still star hop. I will start with a “marker” star that should be easily visible unaided on a night capable of supporting this kind of study. The field stars are quite recognizable in the finder and this is an area that takes some work. Because these galaxies approach magnitude 13, they are best suited to the larger telescope.

Now, let’s go between map and sky and identify both Zeta and Eta Crater and form a triangle. Our mark is directly south of Eta the same distance as between the two stars. At low power, the 12.7 magnitude NGC 3981 (Right Ascension: 11 : 56.1 – Declination: -19 : 54) sits inside a stretched triangle of stars. Upon magnification, an elongated, near edge-on spiral structure with a bright nucleus appears. Patience and aversion makes this “stand up” galaxy appear to have a vague fading at the frontiers with faint extensions. A moment of clarity is all it takes to see tiny star caught at the edge.

Tuesday, June 19 – New Moon! Tonight’s first study object, 12.7 magnitude NGC 3956 (Right Ascension: 11 : 54.0 – Declination: -20 : 34) is about a degree due south of NGC 3981. When first viewed, it appears as edge-on structure at low power. Upon study it takes on the form of a highly inclined spiral. A beautiful multiple star, and a difficult double star also resides with the NGC 3956 – appearing almost to triangulate with it. Aversion brings up a very bright core region which over the course of time and study appears to extend away from the center, giving this very sweet galaxy more structure than can be called from it with one observation.

Our next target is a little more than two degrees further south of our last study. The 12.8 magnitude NGC 3955 (Right Ascension: 11 : 54.0 – Declination: -23 : 10) is a very even, elongated spiral structure requiring a minimum of aversion once the mind and eye “see” its position. Not particularly an impressive galaxy, the NGC 3955 does, however, have a star caught at the edge as well. After several viewings, the best structure I can pull from this one is a slight concentration toward the core.

Now we’ll study an interacting pair and all that is required is that you find 31 Corvii, an unaided eye star west of Gamma and Epsilon Corvii. Now we’re ready to nudge the scope about one degree north. The 11th magnitude NGC 4038/39 (Right Ascension: 12 : 01.9 – Declination: -18 : 52) is a tight, but superior pair of interacting galaxies. Often referred to as either the “Ringtail” or the “Antenna”, this pair deeply captured the public’s imagination when photographed by the Hubble. (Unfortunately, we don’t have the Hubble, but what we have is set of optics and the patience to find them.) At low power the pair presents two very stellar core regions surrounded by a curiously shaped nebulosity. Now, drop the power on it and practice patience – because it’s worth it! When that perfect moment of clarity arrives, we have crackling structure. Unusual, clumpy, odd arms appear at strong aversion. Behind all this is a galactic “sheen” that hints at all the beauty seen in the Hubble photographs. It’s a tight little fellow, but worth every moment it takes to find it.

Return to 31 Corvii and head one half degree northwest to discover 11.6 magnitude NGC 4027 (Right Ascension: 11 : 59.5 – Declination: -19 : 16). Relatively large, and faint at low power, this one also deserves both magnification and attention. Why? Because it rocks! It has a wonderful coma shape with a single, unmistakable bold arm. The bright nucleus seems to almost curl along with this arm shape and during aversion a single stellar point appears at its tip. This one is a real treat!

Wednesday, June 20 – Today marks the official date of 2012 Summer Solstice!

With no Moon to contend with in the predawn hours, we welcome the “shooting stars” as we pass through another portion of the Ophiuchid meteor stream. The radiant for this pass will be nearer Sagittarius and the fall rate varies from 8 to 20, but it can sometimes produce unexpectedly more.

Tonight let’s look to the sky again and fixate on Eta Crater – our study lay one half degree southeast. The 12.8 magnitude NGC 4033 (Right Ascension: 12 : 00.6 – Declination: -17 : 51) is a tough call even for a large scope. Appearing elliptical at low power, it does take on some stretch at magnification. It is smallish, even and quite unremarkable. It requires good aversion and a bit of patience to find. Good luck!

The last of our studies resides by a star, one degree west of Beta Corvii. In order to “see” anything even remotely called structure in NGC 4462 (Right Ascension: 12 : 29.3 – Declination: -23 : 10), this one is a high power only galaxy that is best when the accompanying star is kept out of the field as much as possible. It holds a definite stellar nucleus and a concentration that pulls away from it making it almost appear barred. On an exceptional night with a large scope, wide aversion and moments of clarity show what may be three to four glints inside the structure. Ultra tiny pinholes in another universe? Or perhaps an unimaginably huge, bright globular clusters? While attention is focused on trying to draw out these points, you’ll notice this galaxy’s structure much more clearly. Another true beauty and fitting way to end this particular study field!

Thursday, June 21 – Keep an eye out for the exiting planet Mars! It’s been on the move and has now crossed the border of Virgo and returned to Leo. Have you noticed it quickly changing in both apparent brightness and size? It won’t be long until it’s gone! And speaking of planets on the move, have you spotted Mercury yet? You can find the swift little planet low on the western horizon just after sunset. Look for it just to the south of Castor and Pollux!

For challenging larger telescope studies, return to eastern edge of Mare Crisium and Promontorium Agarum to identify shallow crater Condorcet to its east. Look along the shore of the mare for a mountain to the south known as Mons Usov. Just to its north Luna 24 landed and directly to its west are the remains of Luna 15. We’ll study more about them in the future. Can you spot the tiny dark well of crater Fahrenheit nearby? Continue with your telescope north of Mare Crisium for even more challenging features such as northeast limb studies Mare Smythii and Mare Marginis. Between them you will see the long oval crater Jansky – bordered by Jansky A at the very outer edge.

While you’re out tonight, take a look at the skies for a circlet of seven stars that reside about halfway between orange Arcturus and brilliant blue/white Vega. This quiet constellation is named Corona Borealis – or the “Northern Crown.” Just northwest of its brightest star is a huge concentration of over 400 galaxies that reside over a billion light-years away from us. This area is so small from our point of view that we could cover it with our thumbnail held at arm’s length!

For variable star fans, let’s explore Corona Borealis and focus our attention on S – located just west of Theta – the westernmost star in the constellation’s arc formation. At magnitude 5.3, this long-term variable takes almost a year to go through its changes; usually far outshining the 7th magnitude star to its northeast – but will drop to a barely visible magnitude 14 at minimum. Compare it to the eclipsing binary U Coronae Borealis about a degree northwest. In slightly over three days this Algol-type will range by a full magnitude as its companions draw together.

Friday, June 22 – Today celebrates the founding of the Royal Greenwich Observatory in 1675. That’s 332 years of astronomy! Also on this date in history, in 1978, James Christy of the US Naval Observatory in Flagstaff Arizona discovered Pluto’s satellite Charon.

If you’d like to practice some unaided eye astronomy, then look no further than the western skyline as the Sun sets. At twilight you’ll first notice the very slender crescent Moon – but don’t delay your observations as you can spot Mercury to the west! The inner planet will set very fast, so you’ll need an open horizon. But that’s not all… the speedy little dude is lined up perfectly with Castor and Pollux! With the foursome nearly “in a row” this will make a very cool apparition to remind friends and family to watch for!

Now, grab your favorite optics for a selenographic treat tonight return to the area just north of Mare Crisium area to observe spectacular crater Cleomides. This two million year old crater is separated from Crisium by some 60 kilometers of mountainous terrain. Telescopically, Cleomides is a true delight at high power. To Cleomides’ east, begin by identifying Delmotte, and to the northwest, Trailes and Debes. About twice Clemoides’ width northwest, you will see a sharply well-defined Class I crater Geminus. Named for the Greek astronomer and mathematician Geminos, this 86 kilometer wide crater shows a smooth floor and displays a long, low dune across its middle.

When you’re finished, point your binoculars or telescopes back towards Corona Borealis and about three fingerwidths northwest of Alpha for variable star R (Ra 15. 48.6 Dec +28 09). This star is a total enigma. Discovered in 1795, most of the time R carries a magnitude near 6, but can drop to magnitude 14 in a matter of weeks – only to unexpectedly brighten again! It is believed that R emits a carbon cloud which blocks its light. When studied at minima, the light curve resembles a “reverse nova,” and has a peculiar spectrum. It is very possible this ancient Population II star has used all of its hydrogen fuel and is now fusing helium to carbon. It’s so odd that science can’t even directly determine its distance!

Saturday, June 23 – If you missed yesterday’s apparition of Mercury, then try again tonight. While the small planet might be dim, just look for the brighter pairing of Castor and Pollux above the western horizon at twilight. Can’t find it? Then try this. When you look at this famous pair of stars, judge the distance between the two. Now, apply that same distance and angle to the left (southern) star, Pollux, and you’ve found Mercury! Need more? Then check out the Moon and you’ll see Regulus is about a fistwidth to the east/southeast and Mars is a little more than two handspans to the southeast. Still more? Then continue on from Mars southeast about about another two handspans and you’ll see the pairing of Spica and Saturn!

Using your telescope tonight on the Moon will call up previous study craters, Atlas and Hercules to the lunar north. If you walk along the terminator to the due west of Atlas and Hercules, you’ll see the punctuation of 40 kilometer wide Burg just emerging from the shadows. While it doesn’t appear to be a grand crater just yet, it has a redeeming feature – it’s deep – real deep. If Burg were filled with water here on Earth, it would require a deep submergence vehicle like ALVIN to reach its 3680 meter floor! This class II crater stands nearly alone on an expanse of lunarscape known as Lacus Mortis. If the terminator has advanced enough at your time of viewing, you may be able to see this walled-plain’s western boundary peeking out of the shadows.

While we’re out, let’s have a look at Delta Serpens. To the eye and binoculars, 4th magnitude Delta is a widely separated visual double star… But power up in the telescope to have a look at a wonderfully difficult binary. Divided by no more than 4 arc seconds, 210 light-year distant Delta and its 5th magnitude companion could be as old as 800 million years and on the verge of becoming evolved giants. Separated by about 9 times the distance of Pluto from our Sun, the white primary is a Delta Scuti-type variable which changes subtly in less than four hours. Although it takes the pair 3200 years to orbit each other, you’ll find Delta Serpens to be an excellent challenge for your optics.

Sunday, June 24 – On this day in 1881, Sir William Huggins made the first photographic spectrum of a comet (1881 III) and discovered cyanogen (CN) emission at violet wavelengths. Unfortunately, his discovery caused public panic around 29 years later when Earth passed through the tail of Halley’s Comet. What a shame the public didn’t realize that cyanogens are also released organically! More than fearing what is in a comet’s tail, they should have been thinking about what might happen should a comet strike. Tonight look at the wasted Southern Highland area of the Moon with new eyes… Many of these craters you see were caused by impacts – some as large as the nucleus of Halley itself.

Now let’s pick up a binocular curiosity located on the northeast shore of Mare Serenitatis. Re-identify the bright ring of Posidonius, which contains several equally bright points both around and within it – and look at Mare Crisium and get a feel for its size. A little more than one Crisium’s length west of Posidonius you’ll meet Aristotle and Eudoxus. Drop a similar length south and you will be at the tiny, bright crater Linne on the expanse of Mare Serenitatis. So what’s so cool about this little white dot? With only binoculars you are resolving a crater that is one mile wide, in a seven mile wide patch of bright ejecta – from close to 400,000 kilometers away! While you were there, did you notice how much Proclus has changed tonight? It is now a bright circle and beginning to show bright lunar rays…

Before we head for deep sky, be sure to at least take a look at Saturn and Mars. Right now the Ring King has reached its greatest westward position and will begin its tour back to the east. Now, check out Mars’ position to the west and measure with your hands roughly how far apart they are. At this point they are separated by about two handspans. Check again in a few weeks to see planetary motion displayed right before your eyes!

Now let’s turn binoculars or telescopes towards magnitude 2.7 Alpha Librae – the second brightest star in the celestial “Scales.” Its proper name is Zuben El Genubi, and even as “Star Wars” as that sounds, the “Southern Claw” is actually quite close to home at a distance of only 65 light-years. No matter what size optics you are using, you’ll easily see Alpha’s 5th magnitude companion widely spaced and sharing the same proper motion. Alpha itself is a spectroscopic binary which was verified during an occultation event, and its inseparable companion is only a half magnitude dimmer according to the light curves. Enjoy this easy pair tonight!

Until next week? Ask for the Moon… But keep on reaching for the stars!

Weekly SkyWatcher’s Forecast – February 27-March 4, 2012


Greetings, fellow SkyWatchers! It’s going to be a great week for lunar studies and an even better time to study some interesting single stars. Need more? Then keep an eye on the skies as the Delta Leonid meteor shower heats up towards its later week peak. Get out those binoculars and telescopes and I’ll see you in the backyard…

Monday, February 27 – With tonight’s Moon in a much higher position to observe, let’s begin with an investigation of Mare Fecunditatis – the Sea of Fertility. Stretching 1463 kilometers in diameter, the combined area of this mare is equal in size to the Great Sandy Desert in Australia – and almost as vacant in interior features. It is home to glasses, pyroxenes, feldspars, oxides, olivines, troilite and metals in its lunar soil, which is called regolith. Studies show the basaltic flow inside of the Fecunditatis basin perhaps occurred all at once, making its chemical composition different from other maria. The lower titanium content means it is between 3.1 and 3.6 billion years old!

The western edge of Fecunditatis is home to features we share terrestrially – grabens. These down-dropped areas of landscape between parallel fault lines occur where the crust is stretched to the breaking point. On Earth, these happen along tectonic plates, but on the Moon they are found around basins. The forces created by lava flow increase the weight inside the basin, causing a tension along the border which eventually fault and cause these areas. Look closely along the western shore of Fecunditatis where you will see many such features.

Today is the birthday of Bernard Lyot. Born in 1897, Lyot went on to become the inventor of the coronagraph in 1930. By all accounts, Lyot was a wonderful and generous man who sadly died of a heart attack when returning from a trip to view a total eclipse. Although we cannot hand you a corona, we can show you a star that wears its own gaseous envelope.

Let’s go to our maps west of M36 and M38 to identify AE Aurigae. As an unusual variable, AE is normally around 6th magnitude and resides approximately 1600 light years distant. The beauty in this region is not particularly the star itself but the faint nebula in which it resides known as IC 405, an area of mostly dust and very little gas. What makes this view so entertaining is that we are looking at a “runaway” star. It is believed that AE once originated from the M42 region in Orion. Cruising along at a very respectable speed of 80 miles per second, AE flew the “stellar nest” some 2.7 million years ago! Although IC 405 is not directly related to AE, there is evidence within the nebula that areas have been cleared of their dust by the rapid northward motion of the star. AE’s hot, blue illumination and high energy photons fuel what little gas is contained within the region. Its light also reflects off the surrounding dust. Although we cannot “see” with our eyes like a photograph, together the pair forms an outstanding view for the small backyard telescope and it is known as “The Flaming Star.”

Tuesday, February 28 – Since the stars of our study constellation of Monoceros are quite dim when the Moon begins to interfere, why not spend a few days really taking a look at the Moon’s surface and familiarizing yourself with its many features? Tonight would be a great time for us to explore “The Sea of Nectar.” At around 1000 meters deep, Mare Nectaris covers an area of the Moon equal to that of the Great Sandhills in Saskatchewan, Canada. Like all maria, it is part of a gigantic basin that is filled with lava, and evidence of grabens exists along its western basin edge. While Nectaris’ basaltic flows appear darker than those in most maria, it is one of the older formations on the Moon and as the terminator progress, you’ll be able to see where ejecta belonging to Tycho crosses its surface. For now? Let’s have a closer look at the mare itself and its surrounding craters… Enjoy these many features which are also lunar challenges – and we’ll be back to study each later in the year!

Now, let’s have a look about a fistwidth north-northwest of Sirius – for Beta Monocerotis. Discovered by Sir William Herschel in 1781, Beta is perhaps one of the most outstanding triple systems in the sky, with each of its three bright, white components near equal magnitude. Residing about 100-200 light-years away, these identical spectral type stars are separated by no more than 400 AU and don’t appear to have changed positions since measured by Struve in 1831. Although you won’t be able to split this system with binoculars, even a small telescope will pick apart their brilliancy and make Beta a star to remember!

Wednesday, February 29 – Tonight let your imagination sweep you away as we go mountain climbing – on the Moon! Tonight all of Mare Serenitatis will be revealed and along its northwestern shore lie some of the most beautiful mountain ranges you’ll ever view – The Caucasus to the north and the Apennines to the south. Like its earthly counterpart, the Caucasus Mountain range stretches almost 550 kilometers and some of its peaks reach upwards to 6 kilometers – a summit as high as Mount Elbrus!

Slightly smaller than its terrestrial namesake, the lunar Apennine mountain range extends some 600 kilometers with peaks rising as high as 5 kilometers. Be sure to look for Mons Hadley, one of the tallest peaks that you will see at the northern end of this chain. It rises above the surface to a height of 4.6 kilometers, making that single mountain about the size of asteroid Toutatis.

Thursday, March 1 – In 1966 Venera 3 became the first craft to touch another world as it impacted Venus. Although its communications failed before it could transmit data, it was a milestone achievement.

George Abell was born on this day in 1927. Abell was the man responsible for cataloging 2712 clusters of galaxies from the Palomar sky survey, which was completed in 1958. Using these plates, Abell put forth the idea that the grouping of such clusters distinguished the arrangement of matter in the universe. He developed the “luminosity function,” which shows relationship between brightness and number of members in each cluster, allowing you to infer their distances. Abell also discovered a number of planetary nebulae and developed the theory (along with Peter Goldreich) of their evolution from red giants. Abell was a fascinating lecturer and a developer of many television series dedicated to explaining science and astronomy in a fun and easy to understand format. He was also a president and member of the Board of Directors for the Astronomical Society of the Pacific, as well as serving in the American Astronomical Society, the Cosmology Commission of the International Astronomical Union, and he accepted editorship of the Astronomical Journal just before he died.

Tonight your lunar assignments are relatively easy. We will begin by identifying “The Sea of Vapors.” Look for Mare Vaporum on the southwest shore of Mare Serenitatis. Formed from newer lava flow inside an old crater, this lunar sea is edged to its north by the mighty Apennine Mountains. On its northeastern edge, look for the now washed-out Haemus Mountains. Can you see where lava flow has reached them? This lava has come from different time periods and the slightly different colorations are easy to spot even with binoculars.

Further south and edged by the terminator is Sinus Medii – “The Bay in the Middle.” With an area about the size of both Massachusetts and Connecticut, this lunar feature is the mid-point of the visible lunar surface. In 1930, experiments were underway to test this region for surface temperature – a project begun by Lord Rosse in 1868. Surprisingly enough, results of the two studies were very close, and during full daylight temperatures in Sinus Medii can reach the boiling point as evidenced by Surveyors 4 and 6 – which landed near its center.

Now take a hop north of Mare Vaporum for a look at “The Rotten Swamp” – Palus Putredinus. More pleasingly known as the “Marsh of Decay,” this nearly level surface of lava flow is also home to a mission – the hard-landing of Lunik 2. On September 13, 1959 astronomers in Europe reported seeing the black dot of the crashing probe. The event lasted for nearly 300 seconds and spread over an area of 40 kilometers

Friday, March 2 – Tonight it’s time to relax and enjoy the Delta Leonid meteor shower. Burning through our atmosphere at speeds of up to 24 kilometers per second, these slow travelers will seem to radiate from a point around the middle of Leo’s “back.” The fall rate is rather slow at around 5 per hour, but they are still worth keeping a watch for!

Tonight let’s return again to the lunar surface to study how the terminator has moved and take a close look at the way features change as the Sun brightens the moonscape. Can you still see Langrenus? How about Theophilus, Cyrillus and Catharina? Does Posidonius still look the same? Each night features further east become brighter and harder to distinguish – yet they also change in subtle and unexpected ways. We’ll look at that in the days ahead, but tonight let’s walk the terminator as one of the most beautiful features has now come into view – “The Bay of Rainbows.” Sinus Iridum’s C-shape is easily recognizable in even small binoculars – yet there are a wonderland of small details in and around the area for the small telescope that we’ll study as the year goes by.

Saturday, March 3 – Tonight’s bright skies are brought to you by the Moon! Have you noticed how difficult it is to see any stars belonging to Monoceros with these conditions? Don’t worry. We’ll be back. For now, let’s continue onwards with our lunar studies as we locate the emerging “Sea Of Islands.” Mare Insularum will be partially revealed tonight as one of the most prominent of lunar craters – Copernicus – now comes into view. While only a small section of this reasonably young mare is now visible southeast of Copernicus, the lighting will be just right to spot its many different colored lava flows. To the northeast is a lunar club challenge: Sinus Aestuum. Latin for the Bay of Billows, this mare-like region has an approximate diameter of 290 kilometers, and its total area is about the size of the state of New Hampshire. Containing almost no features, this area is low albedo – providing very little surface reflectivity.

Tonight let’s try a lovely triple star system – Beta Monocerotis. Located about a fist width northwest of Sirius, Beta is a distinctive white star with blue companions. Separated by about 7 arc seconds, almost any magnification will distinguish Beta’s 4.7 magnitude primary from its 5.2 magnitude secondary to the southeast. Now, add a little power and you’ll see the fainter secondary has its own 6.2 magnitude companion less than 3 arc seconds away to the east.

Before you call it a night, be sure to have a quick look at Mars. Right now the red planet is at opposition and can be seen from sunset until sunrise in the constellation of Leo. You may have also noticed that it is dimming slightly, too. It has now reached an estimated -1.23 magnitude. Be sure to look for wonderful features like Sytris Major and the polar caps!

Sunday, March 4 – In 1835, Giovanni Schiaparelli opened his eyes for the very first time and opened ours with his accomplishments! As the director of the Milan Observatory, Schiaparelli (and not Percival Lowell) was the fellow who popularized the term “Martian canals” somewhere around the year 1877. Far more importantly, Schiaparelli was the man who made the connection between the orbits of meteoroid streams and the orbits of comets almost eleven years earlier!

Tonight let’s turn binoculars or telescopes toward the southern lunar surface as we set out to view one of the most unusually formed craters – Schiller. Located near the lunar limb, Schiller appears as a strange gash bordered on the southwest in white and black on the northeast. This oblong depression might be the fusion of two or three craters, yet shows no evidence of crater walls on its smooth floor. Schiller’s formation still remains a mystery. Be sure to look for a slight ridge running along the spine of the crater to the north through the telescope. Larger scopes should resolve this feature into a series of tiny dots.

Let’s try our hand at Beta Orionis … the bright, blue/white star in the southwestern corner of Orion. As you may have noticed for the most part – the brighter the stars are, the closer they are. Not so Rigel! As the seventh brightest star in the sky, it breaks all the “rules” by being an amazing 900 light years away! Can you imagine what an awesome supergiant this white hot star really is? Rigel is actually one of the most luminous stars in our galaxy and if it were as close as Sirius it would be 20% as bright as tonight’s Moon! As an added bonus, most average backyard telescopes can also reveal Rigel’s 6.7 magnitude blue companion star. And if these “two” aren’t enough – note the companion is also a spectroscopic double!

Until next week? Ask for the Moon… but keep on reaching for the stars!

If you enjoy the weekly observing column, why not consider buying the fully illustrated book, The Night Sky Companion 2012. It’s available in both a softcover and Kindle format!