Our Night Sky: June 2009

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Our Night Sky, episode 15, features constellation Virgo’s brightest star, Spica, and flaring satellites.

Last month, I talked about using the Big Dipper to locate the red-giant star, Arcturus. From Arcturus, move your gaze down, towards the horizon, to the ecliptic – that apparent path of the Sun, Moon, and planets. There, you’ll find the bright-white Alpha Virginis (or Spica, as it’s more commonly known) along Virgo’s horizon-facing edge. Some of the other stars outlining Virgo (a mythological maiden) include Vendimiatrix, Zavijah, Auva, Porrima, and Heze.

Originally classified as one blue-giant star, for its intense luminosity, Spica is actually two B-class stars and is located some 260 light-years from Earth. Spica is also a variable star; in other words, its apparent magnitude, or brightness, periodically fluctuates. With some variable stars, these fluctuations are visually apparent. With Spica, they are not. What makes Spica’s variability so interesting is that the causes for this light fluctuation are both external and internal. Not only is Spica a rotating ellipsoidal variable (a close binary system whose components are distorting each other,) one of its two stars is also a Beta Cephei (its surface is contracting and expanding, or pulsating.) Both are fascinating scenarios that you can learn more about in the More About section below.

Some of the easiest, yet most spectacular, observations for amateur astronomers are Iridium flares and the International Space Station. Satellites, the space station, space telescopes – like the Hubble, fly over our homes every night, and you can see many of them. The brightest are Iridium communications satellites, which often appear to “flare” when sunlight is reflected by their flat mirror-like surfaces. The ISS does this, too, when sunlight glints off its vast solar panels. These so-called flares are especially prominent in the hours just before sunrise and after sunset, and they are absolutely stunning.

Flares can be predicted with some degree of accuracy, so you can watch for them by checking a flare predictions website like Heavens Above. Heavens Above also notes local flyover times for the space station, Hubble, and other orbiting crafts.

You can use this printable star chart, centered on Virgo, to help you become more familiar with that region surrounding the star, Spica.  The star atlas software, Touring the Universe Through Binoculars Atlas, is also available for free download from TUBA software by Phil Harrington and Dean Williams.


Virgo: Positioned along the ecliptic plane, the constellation Virgo is visible from both the northern and southern hemispheres.  Some of the constellations bordering Virgo include Leo, Bootes, Libra, and Hyda.  Virgo is the second largest constellation in the sky and is home to one of the largest known galaxy clusters, the Virgo Cluster.  This tidally-bound collection of many hundreds of galaxies is positioned within Virgo’s left shoulder, near the borders of Coma Berenices and Leo.  Some of the cluster’s better-known members include several Messier galaxies, as well as an eight-galaxy alignment known as Markarian’s Chain.  The cluster’s most famous member is probably M87, wherein resides one of the most massive and violent black holes known.

Spica: At magnitude 1.04, Spica is the fifteenth brightest star in the sky and constellation Virgo’s brightest.  It is also the brightest-known rotating ellipsoidal variable star.  Though Spica’s two primary components are best-known, Spica is actually comprised of five stars, the other three being evidenced only during lunar occultations.  The two primary stars are ultra-luminous giants whose mutual orbits bring them within just .012 AU of each other.  Because of its position along the ecliptic, Spica is often occulted by the Moon.  This same near-ecliptic position, coupled with its brightness, suggest that Spica is the star that enabled Greek astronomer Hipparchus’ independent discovery of the precession of the equinoxes more than two-thousand years ago.

Variable Stars: Simply put, a variable star is one which changes in brightness.  In other words, its apparent magnitude fluctuates.  These changes can be attributed to a variety of physical factors, including eclipses by companion stars, interactions with other stars, and surface pulsations.  Variable stars are classified according to causation – whether it is self-involved (intrinsic) or related to another star (extrinsic).  These two classes are further divided according to specificity.  Most variable stars are either extrinsic or intrinsic, but Spica is both!

Observing flares: The best time to observe Iridium satellites and the International Space Station is around sunset and sunrise, when the satellites’ antennae and the space stations solar arrays best reflect sunlight.  One of the most reliable sources for flare predictions is Heavens-Above.  Registration is simple and free but necessary in order to predict flyovers specific to your location.  Flaring satellites and the space station first appear in the sky as a distant faint point of light that steadily brightens as the craft approaches and then momentarily appears to flare, like a suddenly brightening star, as the craft reaches its highest apparent position.  As the craft continues on, that reflected point of light steadily decreases.  In this long-exposure image, that makes a moving single point of light appear as en extended line, we can see the fainter tapered ends and the brighter center as Iridium satellite SVO55 traversed a SSW horizon.  You can learn more about Iridium communications satellites, here, and more about flares, here.

Orbiting satellites and spacecrafts: Did you know that hundreds of thousands, possibly even millions, of man-made objects orbit our planet?  These objects range from tiny bits of debris to defunct satellites, and together they present a real hazard to working crafts, including space-based observatories and the International Space Station.  You can see many of these orbiting crafts and sometimes even smaller objects, like an astronaut’s lost tool bag, as very faint points of light moving across the sky.  Most do require binoculars, but they are fun to watch, especially when you know what each one is.  There are even two prototype hotels orbiting our planet.  Flyovers for your region can be found on several online prediction sites, including the afore-mentioned Heavens-Above site, as well as Spaceweather’s Satellite Flybys and N2YO Real-Time Satellite Tracking.

Saturn and the Moon Tonight

This evening, you’ll find the first-quarter moon between Saturn and bright Regulus.  Looking WSW, Saturn is just eight degrees above and slightly left of Luna, while Regulus is that bright star seven degrees right of the Moon.

Although these three objects may appear close to each other, quite the opposite is true.  The Moon orbits our planet at an average distance of 239,000 miles; Saturn is a bit further, orbiting the Sun at about 890 million miles; while Regulus is not even in our solar system – it is located some 77 light-years away in the constellation Leo.

Not only are these objects very distant from each other, they are very different, as well.  The Moon is a cold, dry, solid orb with a diameter of about 3500 km ; Saturn is a giant gaseous planet with a diameter ten times that of Earth’s; and Regulus is hot blue-giant about four times the size of our Sun.

All three objects set by about midnight, so get out there early and take a pair of binoculars for an up-close look!

Crescent Moon at Sunset

Watch your WNW horizon just after sunset this evening to see the New Moon, less than 48 hours old, setting with the constellation Taurus.  Luna reached New moon at 12:11 UT (that’s 8:11 am EDT) on Sunday morning, so it will appear as a very thin crescent, slightly ENE of Beta Tauri (aka El Nath,) a giant class-B star located about 130 LY distant.

Not so apparent, positioned east of Beta Tauri, very close to Zeta Tauri, is the famous Crab Nebula, the remnants of a supernova witnessed by Chinese astronomers nearly one-thousand years ago.  Also very nearby, above and west of Beta Tauri, are the famous open clusters of Auriga – M36, M37, and M38.  While the Crab Nebula is best targeted with a telescope, Auriga’s clusters are especially lovely through binoculars.

Tonight’s sunset with a nearly-new Luna offers an excellent opportunity for pictures.  If you capture any images, share them with the Astrocast.TV team, here, in the comments section of this blog.  We’d love to see them!

A Picture-Perfect Morning Sky

Early Thursday morning offers a picture-perfect scene, with Venus, Mars, and the crescent moon rising as a trio on your East horizon, in the hours just before sunrise.  Look a little higher, to your SSE horizon, and there you’ll find bright Jupiter with three of its four Galilean moons.

You’ll need binoculars to see those moons leading W from Jupiter.  Left to right, they are Io, Ganymede, and Callisto.  The fourth moon, Europa, will be lost in Jupiter’s shadow as it begins its pass behind the giant planet.  That bright star just above the three moons will be Mu Capricorni, a 5th magnitude star more than 90 LY away.  For a real challenge, look just NE of Jupiter to see if you can distinguish the much more distant, and very faint, Neptune from the surrounding background stars.

While you’re skywatching, check the Heavens Above website to see if Space Shuttle Atlantis will be passing over your region as that crew heads home from NASA’s final Hubble servicing mission.  Atlantis will appear as a distant moving star, brightening slightly near its highest point and fading again as it disappears back into the horizon.

Look Up to See Hubble!

Today, at 14:01 EDT, Space Shuttle Atlantis launched from Kennedy Space Center for a fourth and final servicing mission to the Hubble Space Telescope.  Scheduled to arrive to the orbiting telescope on Wednesday, the seven-member crew will conduct five EVAs to repair science instruments, install new cameras, and replace batteries, thermal blankets, and gyroscopes.  The 11-day, $1-billion mission can be followed through Mission Specialist, Mike Massimino’s Twitter account, NASA’s Mission to Hubble page, and live on NASA-TV.

You can also follow Shuttle Atlantis and the Hubble Space Telescope from your backyard, simply by looking up.  You can find fly-over times for your region at Heavens Above and NASA’s Satellite Tracking.  Ranging between first and fourth magnitudes, Hubble is not as bright as other orbiting crafts, like Iridium satellites or the ISS, so you will need binoculars.  Bright or not, its an exciting experience to watch the Hubble pass overhead, especially when you know that there are astronauts there, servicing the telescope as it orbits our planet!

Our Night Sky: May 2009

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Our Night Sky Episode 14 features the season’s brightest star and a beautiful morning lineup for the month of May.

Looking high in the sky – slightly East, early in the evening, early in the month, and straight overhead as the evening and month progresses – you’ll find the very bright, orange-tinted Arcturus, constellation Bootes’ brightest star.  If you’re familiar with the Big Dipper, you can follow the arc of the dipper’s handle directly to Arcturus.

Look more closely, and you’ll see that Arcturus sits as the bottom point of a six-starred kite, with four additional stars trailing beneath Arcturus as the kite’s tail.  This kite, with its additional “arm” stars, outlines the constellation Bootes, a herdsman in ancient cultures.

Arcturus is a red-giant star 113 times more luminous than our Sun.  It is our sky’s 3rd brightest star and is located some 37 light years away.  A light year is the distance that light travels in one year and is equal to almost 6 trillion miles.  To compare, using this light-travel time scale, Pluto, at about 4 billion miles, is just 5 light hours away.

Now, here’s a challenge.  Using binoculars, look just ten degrees (about the width of your fist at arm’s length) to Arcturus’ NW. Take your time scanning the region and you’ll run across a fuzzy round patch.  That is the globular cluster M3 – a gravitationally bound collection of about half-a-million stars located in Bootes’ neighboring constellation, Canes Venatici.

Five planets grace the morning sky the entire month of May.  Venus and Mars rise as a pair in the hours just before sunrise on your East horizon.  Venus appears as a bright star – Mars has an orange hue. Jupiter rises on your SE horizon about an hour before Venus and Mars. See if you can spot Jupiter’s four Galilean moons with your binoculars.  Faint Neptune is there, as well, slightly E of Jupiter, as is the equally faint Uranus, in that diagonal region between Jupiter and Venus.  Luna highlights the scene midmonth, posing with Jupiter on the 16th and 17th and as a crescent with Venus & Mars on the 21st.

You can click here for a printable star chart centered on Bootes and the Big Dipper.  The software, Touring the Universe Through Binoculars Atlas, is free to download from TUBA Software by Phil Harrington and Dean Williams.


Bootes: Bootes is a northern hemisphere constellation positioned between Draco and Ursa Major to the north, Canes Venatici and to the west, Virgo to the south, and Hercules, Corona Borealis, and Serpens Caput to the east.  The globular cluster, NGC 5466, and a large number of double-stars can be found in Bootes, offering an enjoyable challenge for binoculars observing.  Bootes is also home to the Bootes Void, a vastly empty region of space located 700-million light years away and spanning some 300-million light years across.

Arcturus: Arcturus is an orange subgiant K star with temperatures ranging around 3600 to 4900 C.  Not only is it Bootes’ alpha star, Arcturus is the second brightest star in the northern hemisphere and was one of the first stars to have its proper motion measured.  While this star has nearly twenty times the radius of our Sun, it has only about 1.5 times the mass.  This is because most red-giant stars are really, originally, sun-like stars that have evolved to expand their outer layers, with much of their size being simply bloated atmosphere.

M3: M3 is a gravitationally bound collection of about half-a-million stars spanning across a 180 LY region.  This cluster resides some 34,000 LY away in the constellation Canes Venatici, looking towards the center of the Milky Way.  Though better seen with binoculars, and best seen with a telescope, M3 is actually visible to the unaided eye in darker skies.  Globular clusters, like M3, are among the oldest known objects in our galaxy.  They orbit the galactic center as a halo above the galactic plane, following a path that often takes them beyond the outer regions of the galaxy and back in again.

Backyard Observing: 1) Choose an area that is both safe and dark. Your house, sheds, and even trees can help to shield against neighboring lights.  2) Carry a flashlight to avoid accidents, especially with younger children.  You can cover the end of your flashlight with red cellophane, or even purchase a specially-filtered flashlight from your local department store, to avoid flooding your eyes with light.  3) Make yourself comfortable and permit your eyes to adapt to the darkness. You’ll find that the longer you’re outside, the more stars you’ll begin to see.  4) Be patient  – give yourself time plenty of time to become familiar with the sky.  See if you can recognize star patterns and compare them with a planisphere to learn which constellations are where.  5) Use special care when observing near the setting or rising sun, and never look directly at the sun without solar-filtered binoculars or telescopes.

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