The Constellation Boötes

The northern constellation of Bootes, one of the 88 modern constellations recognized by the IAU. Credit:

Welcome back to Constellation Friday! Today, in honor of our dear friend and contributor, Tammy Plotner, we examine the Bootes constellation. Enjoy!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of the then-known 48 constellations. Until the development of modern astronomy, his treatise (known as the Almagest) would serve as the authoritative source of astronomy. This list has since come to be expanded to include the 88 constellation that are recognized by the International Astronomical Union (IAU) today.

The constellation Boötes (pronounced Bu-Oh-Tays) is one of these constellations, and was also among those listed in the Almagest. It is frequently called the “Watcher of the Bear”, guarding over the northern constellations of both Ursa Major and Ursa Minor (the Greater and Lesser Bears). It is bordered by Canes Venatici, Coma Berenices, Corona Borealis, Draco, Hercules, Serpens Caput, Virgo and Ursa Major.

Name and Meaning:

According to myth, Boötes is credited for inventing the plough, which prompted the goddess Ceres – a goddess of agriculture, grain crops, fertility and motherly love – to place him in the heavens. There are also versions where Bootes represents a form of Atlas, holding up the weight of the world as it turns on its axis (yet another of Hercules’ labors).

Most commonly, Boötes is taken to represent Arcas, the son of Zeus and Callisto. In this source, Arcas was brought up by Callisto father, the Arcadian king Lycaon. One day, Lycaon decided to test Zeus by serving him his own son for a meal. Zeus saw through Lycaon’s intentions and transformed the king into a wolf, killed his sons, and brought Arcas back to life.

Boötes as depicted in Urania's Mirror, a set of constellation cards published in London c.1825. In his left hand he holds his hunting dogs, Canes Venatici. Below them is the constellation Coma Berenices. Above the head of Boötes is Quadrans Muralis, now obsolete, but which lives on as the name of the early January Quadrantid meteor shower. Mons Mænalus can be seen at his feet. Credit: Wikipedia Commons/Sidney Hall
Boötes as depicted in Urania’s Mirror, a set of constellation cards published in London c.1825. Credit: Wikipedia Commons/Sidney

Having heard of her husband’s infidelity, Zeus’ wife Hera transformed Callisto into a bear. For years, she roamed the woods until she met her son, who was now grown up. Arcas didn’t recognize his mother and began to chase her. To avoid a tragic end, Zeus intervened by placing them both in the sky, where Callisto became Ursa Major (aka. The Big Dipper, or “Great Bear”) and Arcas became Boötes.

In another story, Boötes is taken to represent Icarius, a grape grower who was given the secret of wine-making by Dionysus. Icarius used this to create a wonderful wine that he shared with all his neighbors. After overindulging, they woke up the next day with terrible hangovers and believed Icarius had tried to poison them. They killed him in his sleep, and a saddened Dionysus placed his friend among the stars.

Notable Features:

Bootes contains the third brightest star in the night sky – Arcturus (aka. alpha Boötis) – whose Greek name “Arktos” also means “bear”, and is associated with all things northern (including the aurora). Arcturus is quite important, being a type K1.5 IIIpe red giant star. The letters “pe” stand for “peculiar emission,” which indicates the spectrum of the star is unusual and full of emission lines. This is not uncommon in red giants, but Arcturus is particularly strong.

The Bootes contellation. Credit: IAU/Sky and Telescope
The location of the Bootes contellation. Credit: IAU/Sky and Telescope

Arcturus is about 110 times more luminous than our nearest star, but the total power output is about 180 times that of the Sun (when infrared radiation is considered). Arcturus is also notable for its high proper motion, larger than any first magnitude star in the stellar neighborhood other than Alpha Centauri. It is now almost at its closest and is moving rapidly (122 km/s) relative to the Solar System.

Arcturus is also thought to be an old disk star, and appears to be moving with a group of 52 others of its type. Its mass is hard to determine exactly, but it may have the same mass as Sol, or perhaps 1.5 times as much. Arcturus may also be older than the Sun, and much like what the Sun will be in its Red Giant Phase.

Arcturus achieved fame when its light was used to open the 1933 Chicago World’s Fair. The star was chosen because it was thought that light from the star had started its journey at about the same time of the previous Chicago World’s Fair (1893). Technically the star is 36.7 light years away, so the light would have started its journey in 1896. Arcturus’ light was still focused onto a cell that powered the switch for the lights that eventually shined so bright that Arcturus was no longer visible.

Arcturus, along with its neighboring stars, also form the curious “Colonial Viper” formation, a triangular asterism invented by dedicated SkyWatcher, Ed Murray. It is so-named because it resembles a Colonial Viper being launched from a tube on the TV series Battlestar Galactica. The “Launch Tube” is formed by the intersection of Arcturus, Alphekka (Alpha Corona Borealis) and Gamma Bootis, while Izar (Epsilon Bootes) is the Viper.

A Colonial Viper leaving the Launch Tube aboard the Battlestar Galactica. Credit:
A Colonial Viper leaving the Launch Tube aboard the Battlestar Galactica. Credit:

Other notable stars include Nekkar (Beta Boötis), a yellow G-type giant that is 219 light years from Earth. It is a flare star, which is a type of variable star that shows dramatic increases in luminosity for a few minutes. The name Nekkar derives from the Arabic word for “cattle driver”. Then there’s Seginus (Gamma Boötis), a Delta-Scuti type variable star that is approximately 85 light years from Earth. It shows variations in its brightness due to both radial and non-radial pulsations on its surface.

Izar (Epislon Boötis) is a binary star located approximately 300 light years away which consists of a bright orange giant and a smaller and fainter main sequence star. Epsilon Boötis is also sometimes knows as Pulcherrima, which means “the lovieliest” in Latin. The name Izar comes from the Arabic word for “veil.” The star’s other traditional names are Mirak (“the loins” in Arabic) and Mizar.

Muphrid (Eta Boötis) is a spectroscopic binary star that is 37 light years from Earth and close to Arcturus in the sky. The star’s traditional name is Muphrid, derived from the Arabic phrase for “the single one of the lancer.” It belongs to the spectral class G0 IV and has a significant excess of elements heavier than hydrogen.

Boötes is also home to many Deep Sky Objects. This includes the Boötes void (aka. the Great Void, the Supervoid). This sphere-shaped region of the sky is almost 250 million light years in diameter and contains 60 galaxies. The void was originally discovered by Robert P. Kirshner – a Harvard College Professor of Astronomy – in 1981, as part of a survey of galactic redshifts.

The very loose globular cluster NGC 5466, Credit: NASA, ESA
The very loose globular cluster NGC 5466 located in the Boots consetllation, Credit: NASA, ESA/Wikisky

Then there is the Boötes Dwarf Galaxy (Boötes I), a dwarf spheroidal galaxy located approximately 197,000 light years from Earth that measures about 720 light years across. It was only discovered in 2006, owing to the fact that it is one of the faintest galaxies known (with an absolute magnitude of -5.8 and apparent magnitude of 13.1). Boötes I orbits the Milky Way and is believed to be tidally disrupted by its gravity, as evidenced by its shape.

And there’s also NGC 5466, a globular cluster approximately 51,800 light years from Earth and 52,800 light years from the Galactic center. The cluster was first discovered by the German-born British astronomer William Herschel in 1784. It is believed that this cluster is the source of a star stream called the 45 Degree Tidal Stream, which was discovered in 2006.

History of Observation:

The earliest recorded mentions of the stars associated with Boötes come from ancient Babylonia, where it was listed as SHU.PA. These stars were apparently depicted as the god Enlil, who was the leader of the Babylonian pantheon and special patron of farmers. It is likely that this is the source of mythological representations of Bootes as “the ploughman” in Greco-Roman astronomy.

The name Boötes was first used by Homer in The Odyssey as a celestial reference point for navigation. The name literally means “ox-driver” or “herdsman”, and the ancient Greeks saw the asterism now called the “Big Dipper” or “Plough” as a cart with oxen. His dogs, Chara and Asterion, were represented by the constellation of Canes Venatici (the Hunting Dogs) who drove the oxen on and kept the wheels of the sky turning.

The Big Dipper, the asterism that neighbors the Bootes constellation. Credit: Jerry Lodriguss

In traditional Chinese astronomy, many of the stars in Boötes were associated with different Chinese constellations. Arcturus was one of the most prominent, variously designated as the celestial king’s throne (Tian Wang) or the Blue Dragon’s horn (Daijiao). Arcturus was also very important in Chinese celestial mythology because it is the brightest star in the northern sky, and marked the beginning of the lunar calendar.

Flanking Daijiao were the constellations of Yousheti on the right and Zuosheti on the left, which represented the companions that orchestrated the seasons. Dixi, the Emperor’s ceremonial banquet mat, was north of Arcturus. Another northern constellation was Qigong, the Seven Dukes, which was mostly across the Boötes-Hercules border.

The other Chinese constellations made up of the stars of Boötes existed in the modern constellation’s north. These are all representations of weapons –  Tianqiang, the spear; Genghe, variously representing a lance or shield; Xuange, the halberd; and Zhaoyao, either the sword or the spear.

Finding Bootes:

Bootes can be found south of Ursa Major, just off the handle of the Big Dipper. Because the Big Dipper is easy for most observers to find, the handle is used to point to other important stars. Bootes’ brightest star, Arcturus, is also part of a mnemonic device used to orient people, which goes: “Arc to Arcturus, speed on to Spica.” This means you follow the curve in the Dipper’s handle away from Ursa Major until you run into Arcturus. The other star – Spica – is part of the neighboring Virgo constellation.

Arcturus, the brightest star in the Boötes constellation. Credit:
Arcturus, the brightest star in the Boötes constellation. Credit:

For those using binoculars, check out Tau Bootis, a yellow-white dwarf approximately 51 light-years from Earth. It is a binary star system, with the secondary star being a red dwarf. In 1999, an extrasolar planet was confirmed to be orbiting the primary star by a team of astronomers led by Geoff Marcy and R. Paul Butler. Maybe you’d like to look at long term variable star R Boötis? It ranges from 6.2 to 13.1 every 223.4 days.

For those using telescopes, there are plenty of excellent binary star systems to be seen. Pi Boötis is located approximately 317 light years from our solar system and the primary component, P¹ Boötis, is a blue-white B-type main sequence dwarf with an apparent magnitude of +4.49. It’s companion, P² Boötis, is a white A-type main sequence dwarf with an apparent magnitude of +5.88.

Now try looking at Xi Boötis, a binary star system which lies 21.8 light years away. The primary star, Xi Boötis A, is a BY Draconis variable, yellow G-type main sequence dwarf with an apparent magnitude that varies from +4.52 to +4.67. with a period just over 10 days long. Small velocity changes in the orbit of the companion star, Xi Boötis B – an orange K-type main sequence dwarf – indicate the presence of a small companion with less than nine times the mass of Jupiter.

The AB binary can be resolved even through smaller telescopes. The primary star (A) has been identified as a candidate for possessing a Kuiper-like belt, based on infrared observations. The estimated minimum mass of this dust disk is 2.4 times the mass of the Earth’s Moon.

The location of Mu Bootis (Alkalurops) in the Bootes constllation. Credit:
The location of Mu Bootis (Alkalurops) in the Bootes constellation. Credit:

Then there’s the triple system, Mu Boötis. The primary component, Mu¹ Boötis, is a yellow-white F-type sub giant with an apparent magnitude of +4.31. Separated from the primary by 108 arc seconds is the binary star Mu² Boötis, which has a combined spectral type of G1V and a combined brightness of +6.51 magnitudes. The components of Mu² Boötis have apparent magnitudes of +7.2 and +7.8 and are separated by 2.2 arc seconds.

They complete one orbit about their common center of mass every 260 years. How about colorful yellow and blue Kappa Boötis? Kappa2 Boötis is classified as a Delta Scuti type variable star and its brightness varies from magnitude +4.50 to +4.58 with a period of 1.83 hours. The companion star, Kappa¹ Boötis, has magnitude +6.58 and spectral class F1V.

For deep sky observers with large telescopes, try checking out the globular cluster NGC 5466, which is about a fist’s width north of Arcturus. This class XII, 9th magnitude globular was discovered in 1784 by Sir William Herschel and presents an nice challenge for experienced stargazers and amateur astronomers.

Or try compact spiral galaxy NGC 5248. It’s about a fist width south of Arcturus and about a finger width southwest. It’s part of the Virgo cluster of galaxies and could be as far as 50 million light years away. It’s another great grand design spiral which shows spiral galaxy structure when viewed in long exposure photographs. You can mark it on your list as Caldwell 45.

The NGC 5248 spiral galaxy, as imaged with a 32-inch telescope. Credit and Copyright: Adam Block/Mount Lemmon SkyCenter/University of Arizona
The NGC 5248 spiral galaxy, as imaged with a 32-inch telescope. Credit and Copyright: Adam Block/Mount Lemmon SkyCenter/University of Arizona

But if you’d just like to have some fun, then why not try picking out the aforementioned “Colonial Viper and Launch Tube” asterism. If you’re a longstanding Battlestar Galactica fan, then you’ll recognize this ultra-cool spaceship as it sits in its triangular shaped launch tube. To find it, just draw a line between Arcturus, Alphekka (Alpha Corona Borealis) and Gamma Bootis which make up the “Launch Tube”, while Izar (Epsilon Bootes) is the Viper.

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Bootes and Constellation Families.

Messier 5 (M5) – The NGC 5904 Globular Cluster

The globular cluster Messier 5, one of the oldest belonging to the Milky Way. Credit: NASA/ESA/HST

In the late 18th century, Charles Messier was busy hunting for comets in the night sky, and noticed several “nebulous” objects. After initially mistaking them for the comets he was seeking, he began to compile a list of these objects so other astronomers would not make the same mistake. Known as the Messier Catalog, this list consists of 100 objects, consisting of distant galaxies, nebulae, and star clusters.

Among the many famous objects in this catalog is the M5 globular star cluster (aka. NGC 5904). Located in the galactic halo within the Serpens Constellation, this cluster of stars is almost as old as the Universe itself (13 billion years)! Though very distant from Earth and hard to spot, it is a favorite amongst amateur astronomers who swear by its beauty.

Continue reading “Messier 5 (M5) – The NGC 5904 Globular Cluster”

What is the Brightest Star in the Sky, Past and Future?

Brightest Star
Brightest star Sirius (lower center) rules the anthropocene night. Credit and copyright: Alan Dyer.

What’s the brightest star you can see in the sky tonight?

If you live below 83 degrees north latitude, the brightest star in the sky is Canis Alpha Majoris, or Sirius. Seriously, (bad pun intended) the -1st magnitude star is usually the fifth brightest natural object in the sky, and sits high to the south on February evenings… but has it always ruled the night? Continue reading “What is the Brightest Star in the Sky, Past and Future?”

The Curious and Confounding Story Of How Arcturus Electrified Chicago

Find Arcturus easily by using the handle of the Big Dipper. This map shows the sky facing northeast around 9:30-10 p.m. local time in late March. Stellarium

Every star has a story but some are more curious than others. The star Arcturus has an electrifying story with a mysterious twist involving the 1933 World’s Fair.

If you step out on a clear night in mid-March and follow the curve of the Big Dipper’s handle toward the eastern horizon, you’ll come face to face with Arcturus, the 4th brightest star in the sky. Pale orange and fluttering in the low air like a candle in the breeze, Arcturus is a bellwether of spring. By late May it shines high in the south at the onset of night. For the moment, the star hunkers down in the east, sparking through tree branches and over neighborhood rooftops.

The name Arcturus comes from the ancient Greek word “arktos” for bear and means “Bear Watcher”. That’s easy to remember because he follows Ursa Major the Great Bear, the brightest part of which is the Big Dipper, across the spring sky.

Arcturus is 37 light years from Earth and classified as an orange giant star. It spans 25 times the sun's diameter.
Arcturus is 37 light years from Earth and classified as an orange giant star. It spans 25 times the sun’s diameter and shines 113 times more brightly.

It was another spring 80 years ago on May 27,1933, that the city of Chicago opened its Century of Progress Exposition as part of the World’s Fair highlighting progress in science and industry. 40 years prior in 1893 the city had hosted its first big fair, the World’s Columbian Exposition.

In the early 1930s astronomers estimated Arcturus’ distance at 40 light years. Edwin Frost, retired director of the Yerkes Observatory in Williams Bay, Wis., home to the world’s largest refracting telescope, hit upon the idea of using Arcturus to symbolically link both great fairs which were separated by a span of 40 years.

Poster from the Century of Progress Exposition also called the Chicago World's Fair. Its theme was the significance of science and  and improvements brought about by science. The event was celebrated on Chicago's 100th anniversary. Credit: Wikipedia
Poster from the Century of Progress Exposition also called the Chicago World’s Fair. Its theme was the significance of science and how it had bettered mankind. The event was celebrated on Chicago’s 100th anniversary. Credit: Wikipedia

At the time, the photocell, a device that produces an electric current when exposed to light, was all the rage. Clever entrepreneurs had figured out how to take advantage of light’s ability to knock electrons loose from atoms to open doors and count shoppers automatically. They’re still in wide use today from burglar alarms to toilets that magically flush when you step away.

Edwin Frost around the time he was director of Yerkes Observatory in Williams Bay, Wis. Credit: National Academy of Sciences
Edwin Frost around the time he was director of Yerkes Observatory in Williams Bay, Wis. Credit: National Academy of Sciences

Technological innovation through scientific progress was the theme of the 1933 fair. What better way, thought Frost, to highlight the benefits of science and link both great events than by focusing the light of Arcturus onto a photocell and using the electric current generated to flip a switch that would turn on the lights at the fair’s opening.

Though we now know Arcturus is 37 light years away, at the time it was thought to be about 40. The light that left the star during the first world’s fair in 1893 would arrive just in time 40 years later to open the next.  Arcturus was not only at the right distance but bright and easy to see during May at the fair’s opening. Could a more perfect marriage of poetry and science ever be arranged?

Edwin B. Frost (left), Christian T. Elvey (center), and Otto Struve (right) examine a General Electric photoelectric relay and a F.P.-54 Pliotron tube that will help activate the lights of the "Century of Progress," thus opening the Chicago world fair of 1933. University of Chicago Photographic Archive, apf6-00477, Special Collections Research Center, University of Chicago Library.
From left: Edwin B. Frost, Christian T. Elvey, staff, and Otto Struve, Yerkes director, examine a General Electric photoelectric relay and the photocell tube that will help activate the lights of the “Century of Progress,” thus opening the Chicago world fair of 1933. Courtesy Yerkes Observatory

Although Yerkes Observatory was picked for the job, backups were needed in the event of cloudy skies. In the end, telescopes at the University of Illinois Observatory in Urbana, Harvard College Observatory and Allegheny Observatory in Pittsburgh all participated in the grand event.

On May 27, 1933 shortly before the appointed time, Century of Progress Fair president Rufus C. Dawes spoke to a crowd of some 30,000 people assembled in the courtyard at the Hall of Science:

“We recall the great Columbian Exposition of 1893. Never will its beauty be surpassed.
Never will there be held an exposition of more lasting value to this city. It was for Chicago a great triumph.”

Visitors throng the Hall of Science at the Chicago World's Fair in 1933. Click to enlarge Credit: Century of Progress Records, 1927-1952, University of Illinois at Chicago Library (COP_17_0002_00023_027)
Visitors throng the Hall of Science at the Chicago World’s Fair in 1933, site of the Arcturus lighting ceremony. Click to enlarge Credit: Century of Progress Records, 1927-1952, University of Illinois at Chicago Library (COP_17_0002_00023_027)

“We remind ourselves of that triumph tonight by taking rays of light that left the star Arcturus during the period of that exposition and which have traveled at the rate of 186,000 miles a second until at last they have reached us. We shall use these rays to put into operation the mysterious forces of electricity which will make light our grounds, decorate our buildings with brilliant colors, and move the machinery of the exposition.”

Above the speaker’s platform hung a large illuminated panel, the bottom half of which displayed a map of the eastern U.S. with the locations of the four observatories. The top half contained the instruments that completed the circuit from Arcturus to a searchlight in the Hall of Science.

When light beams from the star Arcturus were picked up by photoelectric tubes at four observatories, signals flashed on this display board on the rostrum of the Hall of Science to the show the audience how the official lighting. Click to enlarge. Credit: Century of Progress Records, 1927-1952, University of Illinois at Chicago Library (COP_17_0002_00023_016)
When light beams from the star Arcturus were picked up by photoelectric tubes at four observatories, signals flashed on this display board on the rostrum of the Hall of Science to the show the audience. Click to enlarge. Credit: Century of Progress Records, 1927-1952, University of Illinois at Chicago Library (COP_17_0002_00023_016)

At 9:15 p.m. each of the four observatories borrowed bits of Arcturus’ light, focused them onto their respective photocells and sent the electric current by Western Union telegraph lines to the Chicago fairgrounds.

In the book Fair Management – The Story of a Century of Progress, author Lenox Lohr described what happened next. One of the speakers, probably Philip Fox, director of Chicago’s Adler Planetarium, stepped to the podium to issue the final instructions :

“Harvard, are you ready?”
A red glow ran across the map from Cambridge to Chicago.
“Is Allegheny ready?”
“Illinois ready?”
“Let’s go.”

The switch was thrown, and a searchlight at the top of the Hall of Science shot a great white beam across the sky.”

The crowd went bananas. It was such a huge hit, nearby Elgin Observatory was pressed into operation to light the fair in similar fashion every night for the remainder of the season.

The Hall of Science area at the fair along with the Arcturus sign (far left) and a group of people creating a large star shape on a stage. Click for large version. Credit: Century of Progress Records, 1927-1952, University of Illinois at Chicago Library (COP_17_0002_00023_017)
The Hall of Science area at the fair along with the Arcturus sign (far left) and a group of people creating a large star shape on a stage. Click for large version. Credit: Century of Progress Records, 1927-1952, University of Illinois at Chicago Library (COP_17_0002_00023_017)

Harnessing a distant star for mankind’s benefit. We marvel at the 1933 fair promoters and astronomers for conceiving of this most ingenious way of linking past and present.

That would be the end of a wonderful story if it wasn’t for one Ralph Mansfield. Mansfield, a student at the time at the University of Chicago, worked as a guide at Chicago’s Alder Planetarium, which was also involved in the lighting ceremony. Before passing away in 2007, Mansfield shared the story of how he was the one to point the telescope at Arcturus and fire up the fairground lights.

The Adler Planetarium on Chicago's Lake Michigan lakefront. Credit:Fritz Geller-Grimm
The Adler Planetarium on Chicago’s Lake Michigan lakefront. Credit:Fritz Geller-Grimm

I learned this while reading an article by Nathan B. Myron, PhD on the topic in which Mansfield sought to set the record straight. In his version, then-director of the Adler Planetarium, Philip Fox. was apprehensive about cloudy skies, so he arranged for Mansfield to set up a telescope in the balcony of the Hall of Science. As Fox delivered opening remarks, Mansfield used the Dipper’s Handle to find Arcturus in a lucky break in the clouds, and at the key moment, fed its light to the photocell. The spotlight fired up and the day was saved.

So which is the true story?

“It’s a bit of a mystery,” said Richard Dreiser, public information officer for Yerkes Observatory. “No one really knows absolutely.”

His sentiments were echoed by Bruce Stephenson, current curator at the Adler Planetarium: “The truth as far as we can ascertain it today is not really known. These things happened long ago.”

Most historical accounts indicate that four observatories participated, but Mansfield’s story remains. Will the real version please stand up?

Weekly SkyWatcher’s Forecast: April 23-29, 2012

Mars In Leo - Credit: John Chumack


Greetings, fellow SkyWatchers! What a great week to just enjoy some great unaided eye astronomy observations. Who can resist the beautiful appearance of Mars in Leo? Also this week, you’ll enjoy not one – but two – meteor showers as the Mu Virginids come to town mid-week and the Bootids light up the weekend. Get ready to enjoy bright stars, find planets, explore lunar features, learn some astronomy history and much more! When ever you’re ready, meet me in the back yard…

Monday, April 23 – Pioneer quantum physicist Max Planck was born on this day in 1858. In 1900, Max developed the Planck equation to explain the shape of blackbody spectra (a function of temperature and wavelength of emission). A “blackbody” is any object that absorbs all incident radiation – regardless of wavelength. For example, heated metal has blackbody properties because the energy it radiates is thermal. The blackbody spectrum’s shape remains constant, and the peak and height of an emitter can be measured against it – be it cosmic background radiation – or our own bodies.

Now, let’s put this knowledge into action. Stars themselves approximate blackbody radiators, because their temperature directly controls the color we see. A prime example of a “hot” star is Alpha Virginis, better known as Spica. Compare its color to the cooler Arcturus… What colors do you see? There are other astronomical delights that radiate like blackbodies over some or all parts of the spectrum as well. You can observe a prime example in a nebula such as M42, in Orion. By examining the radio portion of the spectrum, we find the temperature properly matches that of electrons involved in the process of fluorescence. Much like a common household fixture, this process is what produces the visible light we can see.

Tuesday, April 24 – Today in 1970, China launched its first satellite. Named Shi Jian 1, it was a successful technological and research craft. This achievement made China the fifth country to send a vessel into space.

Tonight see if you can spot the tender beginnings of the Moon after sunset. Observers take pleasure in sweeping the sky with small scopes and binoculars in hopes of finding the thinnest possible lunar crescent. And speaking of crescents, did you spot Venus close to the Moon? Why not take out your telescope and see what phase Venus is now in. If you don’t have a filter to cut its bright glare, try wearing sunglasses!

No telescope? No problem. You can still do some very awesome astronomy with just your eyes! Begin with locating the northern constellation of Ursa Major – most commonly known as the “Big Dipper”. Take note of the curve of the Dipper’s “handle” and trace it from the bottom of the cup and continue on the “Arc to Arcturus”. Keep moving, because now you’re going to “Speed on to Spica”! Once you’ve located this bright, blue/white star, simply look to its east/southeast (or upper left) for a yellow appearing “star”. That’s no star… That’s Saturn!

Now let’s have a look at 140 light-year distant Epsilon Hydrae – the northernmost star in the small circlet east of Procyon. While it and Rho will make a beautiful visual double for binoculars, Epsilon itself is a multiple system. Its A and B components are a tough split for any scope, but the 8th magnitude C star is easier. The D component is a dwarf star.

Wednesday, April 25 – Today marks the 15th anniversary of the deployment of Hubble Space Telescope. While everyone in the astronomical community is well aware of what this magnificent telescope “sees,” did you know that you can see it with just your eyes? The HST is a satellite that can be tracked and observed. Visit and enter your location. This page will provide you with a list of visible passes for your area. Although you can’t see details of the scope itself, it’s great fun to track with binoculars or see the Sun glinting off its surface in a scope.

Tonight our first voyage is to the Moon’s surface. Look along the terminator in the southern quadrant and revisit ancient old crater Furnerius. Named for French Jesuit mathematician George Furner, this crater spans approximately 125 kilometers and is a lunar club challenge. Power up and look for two interior craters. The smaller is crater A and it spans a little less than 15 kilometers and drops to a depth of over 1000 meters. The larger crater C is about 20 kilometers in diameter, but goes far deeper, to more than 1400 meters. That’s about as deep as a coral will grow under the Earth’s oceans!

Keep a watch on the skies while you’re out as the Mu Virginid meteor shower reaches its peak at 7 to 10 per hour. With dark skies tonight, you still might catch one of these medium speed meteors radiating from a point near the constellation of Libra.

Thursday, April 26 – On this date in 1920, the Shapely-Curtis debate raged in Washington on the nature of and distance to spiral nebulae. Shapely claimed they were part of one huge galaxy to which we all belonged, while Curtis maintained they were distant galaxies of their own. Thirteen years later on the same date, Arno Penzias was born. He went on to become a Nobel Prize winner for his part in the discovery of the cosmic microwave background radiation, through searching for the source of the “noise” coming from a simple horn antenna. His discovery helped further our understanding of cosmology in ways that Shapely and Curtis could have never dreamed of.

Perhaps they dreamed of Moon? We’ve got Moon! No matter, what we really want to do is revisit and study a changeable, sometimes transient, and eventually bright feature on the lunar surface – crater Proclus. At around 28 kilometers in diameter and 2400 meters deep, Proclus will appear on the terminator on the west mountainous border of Mare Crisium. For many viewers tonight, it will seem to be about 2/3 black, but 1/3 of the exposed crater will be exceptionally brilliant – and with good reason. Proclus has an albedo, or surface reflectivity, of about 16%, which is an unusually high value for a lunar feature. Watch this area over the next few nights as two rays from the crater will widen and lengthen, extending approximately 322 kilometers to both the north and south. Congratulations on another lunar club challenge!

Friday, April 27 – Tonight we’re heading towards the lunar surface to view a very fine old crater on the northwest shore of Mare Nectaris – Theophilus. Slightly south of mid-point on the terminator, this crater contains an unusually large multiple-peaked central mountain which can be spotted in binoculars. Theophilus is an odd crater, one that is a parabola – with no area on the floor being flat. It stretches across a distance of 100 kilometers and dives down 440 meters below the surface. Tonight it will appear dark, shadowed by its massive west wall, but look for sunrise on its 1400 meter summit!

Now, let’s try picking up a globular cluster in Hydra that is located about 3 fingerwidths southeast of Beta Corvus and just a breath northeast of double star A8612 – M68 (Right Ascension:12 : 39.5 – Declination: -26 : 45). This class X globular was discovered in 1780 by Charles Messier and first resolved into individual stars by William Herschel in 1786. At a distance of approximately 33,000 light-years, it contains at least 2000 stars, including 250 giants and 42 variables. It will show as a faint, round glow in binoculars, and small telescopes will perceive individual members. Large telescopes will fully resolve this small globular to the core!

While you’re out, have a look at 27 Hydrae about a fingerwidth southwest of Alpha. It’s an easy double for any equipment with its slightly yellow 5th magnitude primary and distant, white, 7th magnitude secondary. Although it is wide, the pair is a true binary system.

Saturday, April 28 – Today was a very busy day in astronomy history. Newton published his Principia in 1686 on April 28. In 1774, Francis Baily was born. He went on to revise star catalogs and explain the phenomenon at the beginning and ending of a total solar eclipse which we know as “Baily’s Beads.” 1900 saw the birth of Jan Hendrick Oort, who quantified the Milky Way’s rotation characteristics and envisioned the vast, spherical area of comets outside our solar system that we now call the Oort Cloud. Last, but not least, was the birth of Bart Jan Bok in 1906 who studied the structure and dynamics of the Milky Way.

Tonight’s outstanding lunar feature will be crater Maurolycus just southwest of the three rings of Theophilus, Cyrillus and Catharina. This lunar club challenge spans 114 kilometers and goes below the lunar surface by 4730 meters. Be sure to look for Gemma Frisius just to its north.

Now let’s check out a dandy little group of stars that are about a fistwidth southeast of Procyon and just slightly more than a fingerwidth northeast of M48. Called C Hydrae, this group isn’t truly gravitationally bound, but is a real pleasure to large binoculars and telescopes of all sizes. While they share similar spectral types, this mixed magnitude collection will be sure to delight you!

For SkyWatchers, no equipment is necessary to enjoy the Alpha Bootid meteor shower – despite the Moon. Pull up a comfortable seat and face orange Arcturus as it climbs the sky in the east. These slow meteors have a fall rate of 6 to 10 per hour and leave very fine trails, making an evening of quiet contemplation most enjoyable.

Sunday, April 29 – Before we explore space, let’s have a look at the Moon and the close apparition of Regulus and Mars! The three make a wonderful “line up” the night sky! Now, let’s start our lunar observations tonight as challenge craters Cassini and Cassini A come into view just south of the black slash of the Alpine Valley. The major crater spans 57 kilometers and reaches a floor depth of 1240 meters. The challenge is to also spot the central crater A, which is only 17 kilometers wide, yet drops down another 2830 meters below the surface.

While we’re out, have a look at R Hydrae about a fingerwidth east of Gamma – which is a little more than fistwidth south of Spica. R is a beautiful, red, long-term variable first observed by Hevelius in 1662. Located about 325 light-years from us, it’s approaching – but not that fast. Be sure to look for a visual companion star as well!

Until next week? Dreams really do come true when you keep on reaching for the stars!

Many thanks to John Chumack of Galactic Images for his outstanding photo of “Leo In Mars”!

Weekly SkyWatcher’s Forecast: April 9-15, 2012

M95 - Credit: NOAO/AURA/NSF

[/caption]Greetings, fellow SkyWatchers! It’s shaping up to be a great week to enjoy astronomy. For both hemispheres, the Virginid Meteor shower is underway and its peak occurs late Monday night / early Tuesday morning. Need more celestial fireworks? Then keep looking up as the “April Fireballs” will be visiting, with their peak beginning about a week from today and lasting for 24 days. Even if you only catch one of these bright travelers as they sparkle across the starry sky, it will make your night! But hang on, there will be plenty to explore. Bright stars and bright planets are featured – as well as some of the season’s best galaxies. Keep your telescope out and don’t get spooked, because the “Ghost of Jupiter” will be a challenge object! If you want to know more about astonomy history, and what you can see with just your eyes and your optics, then meet me in the back yard…

Monday, April 9 – Tonight let’s take a journey towards the 25th brightest star in the night sky – 1.3 magnitude, Alpha Leonis. Regulus, known as “The Little King,” is the brightest star in Leo. At 77 light-years away, this star is considered a “dwarf” despite shining with a visible light almost 150 times that of Sol. The orange-red giant Arcturus and the blue white “dwarf” Regulus both share a common absolute magnitude very close to 0. The reason the two stars shine with a similar intrinsic brightness – despite widely different physical sizes – is Regulus’ photosphere is more than twice as hot (12,000 C) as Arcturus. While observing Regulus, look for a distant companion of magnitude 8.5. Normally low powers would best concentrate the companion’s light, but try a variety of magnifications to help improve contrast. For those with large aperture scopes, look for a 13.1 magnitude “companion’s companion” a little more than 2 arc seconds away!

Tuesday, April 10 – Be sure to get up before dawn to enjoy the Virginid meteor shower. The radiant point will be near Gamma in the bowl of Virgo. The fall rate of 20 per hour is above average for meteor showers, and with the Moon partially out of the equation this morning, you’re in for a treat!

Tonight, let’s have a look at Arcturus – a star whose distance from the Earth (10 parsecs) and radial velocity (less than 200 meters per second) can almost be considered a benchmark. By skydark you will see 0.2 magnitude, Arcturus – the brightest star in Bootes and 4th brightest star in the night sky – some 30 degrees above the eastern horizon. Apparent to the eye is Arcturus’ orange color. Because a star’s intrinsic luminosity relates to its apparent brightness and distance, Arcturus’ absolute magnitude is almost precisely the same as its apparent magnitude. Just because Arcturus’ radial velocity is nearly zero doesn’t mean it isn’t on the move relative to our Sun. Arcturus is now almost as close as it will ever get and its large proper motion – perpendicular to our line of sight – exceeds 125 kilometers per second. Every 100 years Arcturus moves almost 1 degree across the sky!

Since you’ve looked at a red star, why not look at a red planet before you call it a night? Mars is still making a wonderful apparition. Have you noticed it dimming even more? Right now it should be about magnitude -0.5. You may have noticed something else about Mars in the eyepiece, too… It’s getting smaller!

Wednesday, April 11 – Today is the birthday of William Wallace Campbell. Born in 1862, Campbell went on to become the leader of stellar motion and radial velocity studies. He was the director of Lick Observatory from 1901 to 1930, and also served as president of the University of California and the National Academy of Sciences. Also born on this day – but in 1901 – was Donald H. Menzel – assistant astronomer at Lick Observatory. Menzel became Director of Harvard Observatory, an expert on the Sun’s coronosphere and held a genuine belief in the extraterrestrial nature of UFOs. Today in 1960, the first radio search for extraterrestrial civilizations was started by Frank Drake (Project Ozma). In 1986, Halley’s Comet closed within 65 million kilometers of the Earth – as close as it would get.

Tonight, why don’t we honor Campbell’s work as we try taking a look at a variable ourselves? RT (star 48) Aurigae is a bright cephid that is located roughly halfway between Epsilon Geminorum and Theta Aurigae. This perfect example of a pulsating star follows a precise timetable of 3.728 days and fluxes by close to one magnitude.

Thursday, April 12 – Today in 1961, Yuri Gagarin made one full orbit of the Earth aboard Vostok 1, while also becoming the first human in space. Also today (in 1981) Columbia became the first Space Shuttle to launch.

Break out the telescope tonight and launch your way towards Iota Cancri – a fine wide disparate double of magnitudes 4.0 and 6.6 separated by some 30 arc seconds. This true binary is so distant from one another that they take over 60,000 years to complete a single orbit around their common center of gravity! Located slightly less than a fist’s width due north of M44, this pair is about 300 light years distant. Both stars shine with a light considerably brighter than our Sun and observers may note a subtle gold and pale blue color contrast between them.

Friday, April 13 – With no early evening Moon to contend with, this is a fine opportunity to have a look at a group of galaxies between Leo’s paws. Start at Regulus and look due east toward Iota Leonis. Halfway between the two (less than a fist from Regulus) and two finger-widths northeast of Rho Leonis, you’ll encounter Messier Galaxies M95 (Right Ascension: 10 : 44.0 – Declination: +11 : 42) and M96 (Right Ascension: 10 : 46.8 – Declination: +11 : 49) – both within the same low power field of view. At magnitude 9.2, the brighter – and slightly rounder – M96 lies northeast of 9.7 magnitude, M95. Pierre Mechain discovered both galaxies on March 20, 1781 and Messier added them to his catalog 4 days later. These two galaxies are two of the brightest members of the Leo I galaxy group located some 38 million light-years away.

To see another Messier member of the Leo I group, center on M96 and shift the galaxy south. From the north side of the low power field, the 9.3 magnitude galaxy M105 (Right Ascension: 10 : 47.8 – Declination: +12 : 35), nearby 10th magnitude NGC 3384 (Right Ascension: 10 : 48.3 – Declination: +12 : 38), and 12th magnitude NGC 3389 (Right Ascension: 10 : 48.5 – Declination: +12 : 32) will come into view. M105 was discovered by Mechain on the night Messier catalogued M95 and 96 but was not formally added to Messier’s catalog. Based on Mechain’s observing notes, Helen Sawyer Hogg added it to Messier’s list in 1947 – along with galaxy M106 and globular cluster M107. Mechain failed to notice M105’s bright neighboring galaxy – NGC 3384. NGC 3384 is actually slightly brighter than the faintest Messier discovered – M91.

We’re not done yet! If you center on M105 and shift due north less than a degree and a half you will encounter 10th magnitude NGC 3377 (Right Ascension: 10 : 47.7 – Declination: +13 : 59) – a small elongated galaxy with a stellar core. There are a dozen galaxies visible to moderate amateur instruments (through magnitude 12) in the Leo I region of the sky!

Saturday, April 14 – Today is the birthday of Christian Huygens. Born in 1629, the Dutch scientist went on to become one of the leaders in his field during the 17th century. Among his achievements were promoting the wave theory of light, patenting the pendulum clock, and improving the optics of telescopes by inventing a new type eyepiece and reducing false color through increasing the focal length of refractor telescopes. Huygens was the first to discover Saturn’s rings and largest satellite – Titan. Of the rings, Huygens said, “Saturn: encircled by a ring, thin and flat, nowhere touching, and inclined to the ecliptic.”

Wanna’ check Saturn out? It will be rising in the constellation of Virgo not long after the sky begins to turn dark. If you’re not sure of which “star” it is, just wait for awhile and you’ll find it about a fistwidth northwest of bright, blue/white Spica. Be sure to check out the ring system! Right now they have a very nice southern tilt which will allow you a great view of the shadow of the planet on the rings – and the shadow of the rings on the planet. If the atmosphere will allow, power up! Something you may never have thought of looking for could be happening… Can you see the planet’s edge through the Cassini division? Be sure to look for wide orbiting Titan and some of Saturn’s smaller moons slipping around the ring edges.

Tonight our challenge is also planetary – but it’s the planetary nebula – the “Ghost of Jupiter”. Begin by identifying the constellation of Hydra. Starting at Alpha Hydrae, head east about a fist’s width to find Lambda within a field of nearby fainter stars. Continue less than a fist southeast and locate Mu. You’ll find the “Ghost of Jupiter” (NGC 3242) lurking in the dark less than a finger-width due south. At magnitude 9, the NGC 3242 (Right Ascension: 10 : 24.8 – Declination: -18 : 38) gives a strikingly blue-green appearance in even small scopes – despite being more than 1500 light years away.

Sunday, April 15 – Tonight keep a watch for the “April Fireballs.” This unusual name has been given to what may be a branch of the complex Virginid stream which began earlier in the week. The absolute radiant of the stream is unclear, but most of its long tails will point back toward southeastern skies. These bright bolides can possibly arrive in a flurry – depending on how much Jupiter’s gravity has perturbed the meteoroid stream. Even if you only see one tonight, keep a watch in the days ahead. The time for “April Fireballs” lasts for two weeks. Just seeing one of these brilliant streaks will put a smile on your face!

And if you can’t take your eyes off Leo, then there’s good reason. The combination of Theta Leonis, Regulus and Mars certainly calls attention to itself!

While we’re out, let’s journey this evening towards another lovely multiple system as we explore Beta Monocerotis. Located about a fist width northwest of Sirius, Beta is one of the finest true triple systems for the small telescope. At low power, the 450 light year distant white primary will show the blue B and C stars to the southeast. If skies are stable, up the magnification to split the E/W oriented pair. All three stars are within a magnitude of each other and make Beta one of the finest sights for late winter skies.

If you hadn’t noticed, Saturn is at opposition tonight, meaning it will be viewable from dusk until dawn. Be sure to check out the “Ring King” – but wait until it has risen well above the lower atmosphere disturbance for a superior view!

Until next week, I wish you clear and steady skies!