Sunday, April 1, 2012

Weekly SkyWatcher's Forecast: April 2-8, 2012

Greetings, fellow SkyWatchers! Despite the Moon, it will be a great week as the month of April opens with two meteor showers. The planetary action doesn't stop, because Venus is about to become a "guest star" in the Pleiades! Need more? Then know it's the right time of year to spot aurora - and to gather photons from bright star clusters! Get out your binoculars and telescopes and meet me in the back yard...

Monday, April 2 - Today in 1889, the Harvard Observatory's 13" refractor arrived at Mt. Wilson. Just one month later, it went into astronomical service at Lick Observatory, located at Mt. Hamilton. It was here that the largest telescopes in the world resided from 1908 to 1948 - the 60" for the first decade, followed by the 100". This latter mirror is still the largest solid piece ever cast in plate glass and weighed 4.5 tons. Would you believe it's just 13 inches thick?

Today in 1845, the first photograph of the Sun was taken. While solar photography and observing is the domain of properly filtered telescopes, no special equipment is necessary to see some effects of the Sun - only the correct conditions. Right now Earth's magnetosphere and magnetopause (the point of contact) are positioned correctly to interact with the Sun's influencing interplanetary magnetic field (IMF) - and the plasma stream which flows past us as solar winds. During the time around equinox, this leaves the door wide open for one of the most awesome signs of spring - aurora! Visit the Geophysical Institute to sign up for aurora alerts and use their tools to help locate the position of the Earth's auroral oval.

Tuesday, April 3 - Celestial scenery alert! Tonight as the skies darken, look for a very unusual planetary event… Venus will be visiting the Pleiades! For some parts of the world, it’s possible that it will occult some of the cluster’s member stars, so be sure to check resources for a planetarium program or on-line service that will list times and locations. Enjoy this splendid unaided eye apparition…

While the Moon will be nearly overpowering tonight, let’s take a look at a pair of orbiting bodies as we head for Kappa Puppis – a bright double of near equal magnitudes. This one is well suited to northern observers with small telescopes. For the southern observer, try your hand at Sigma Puppis. At magnitude 3, this bright orange star holds a wide separation from its white 8.5 magnitude companion. Sigma’s B star is a curiosity, because at a distance of 180 light-years it would be about the same brightness as our own Sun placed at that distance!

Wednesday, April 4 - Did you catch last night’s close pass of Venus and the Pleiades? Then try again tonight! It’s not hard to spot blazing Venus above the western horizon just after twilight – and right now it’s a “guest star” in M45!

While you're out tonight, be on watch for the Kappa Serpentid meteor shower. Its radiant will be near the "Northern Crown," the constellation known as Corona Borealis. The fall rate is small with an average 4 or 5 per hour.

Now, let’s identify the upside down Y of the constellation of Cancer. If you can spot the hazy patch of M44, the star just south of it is Delta. About three fingerwidths southeast of Delta is Alpha, and we'll begin by exploring this star… 130 light-year distant Alpha Cancri . Acubens is around 4th magnitude and is also a great double star for a small telescope. Its name translates as the "claw" and you will find it clutches a disparate 11.8 magnitude companion star nearby.

Now hop just one fingerwidth west for a stunning sight - galactic cluster M67 (Right Ascension: 8 : 50.4 - Declination: +11 : 49). Hanging out in space some 2500 light-years away and containing more than 500 members, this grand cluster is a rule breaker in age. Believed to be about 10 billion years old, it is one of the oldest star clusters in our galaxy. Its stars have literally "switched off" from the main sequence, and have passed through the red giant stage and are returning back to their blue youth!

In binoculars you will see it as almost galaxy-like in structure, while even small telescopes resolve individual stars. Large telescopes will reveal stars beyond stars, like a globular cluster that has been smeared across the night. It is truly one of the most beautiful and mysterious of all open clusters.

Thursday, April 5 - We'll return again tonight to Cancer to have a look at some curiosities. The first is about four fingerwidths away from Delta - Zeta Cancri. Its name is Tegmeni and it is a handsome double star for the small telescope. Both components are nearly the same magnitude and neatly split for mid-magnification ranges.

About a fingerwidth due east is V Cancri - a Mira-type variable star. While many such variables are difficult to follow with amateur equipment, V Cancri breaks the rules. It changes from magnitude 7.9 to magnitude 12.8 in a period of 125 days. When it swells to its maximum, it reaches a size about that of the orbit of Mars.

Friday, April 6 - Tonight's Full Moon is often referred to as the "Pink Moon" of April. As strange as the name may sound, it actually comes from the herb known as moss pink - or wild ground phlox. April is the time of blossoming and the "pink" is one of the earliest widespread flowers of the spring season. As always, this Moon is known by other names as well, such as the Full Sprouting Grass Moon, the Egg Moon, and coastal tribes referred to it as the Full Fish Moon. Why? Because spring was the season the fish swam upstream to spawn!

There’s more than one reason to look at the Moon tonight, too. In a span of less than 5 degrees (about 3 fingerwidths held at arm’s length) you’ll see bright Spica almost touching the limb and Saturn just slightly further away. For some lucky viewer somewhere, this could be an occultation or grazing event, so be sure to check resources like IOTA for specific times and locations.

Now let’s move on to 3.2 magnitude – Epsilon Geminorum. Mebsuta is the brightest star (other than Castor) in northwestern Gemini. It has a very distant 9th magnitude companion. As you observe Epsilon, keep in mind its spectral class (G8) is very similar to our Sun. Despite this, Mebsuta glows with an intensity of light 7600 times brighter. It’s one of a rare class of stars called “yellow supergiants” – stars whose nuclear cores are vastly swollen due to advanced age and which have taken on “planetary” proportions. Why planetary? Because the planet Venus would find itself orbiting inside Mebsuta’s 4600 degree C temperature photosphere!

Saturday, April 7 - Today in 1991, the Compton Gamma Ray Observatory (CGRO) was deployed. While it may sound strange, this observatory sees the sky in gamma ray photons. These photons go off the edge of ultra violet - imperceptible to the human eye. Unfortunately, we can't study gamma rays from Earth because our atmosphere blocks it, but the CGRO has shown a universe beyond our direct comprehension.

If there were a place that we could choose to look at in gamma rays, Cancer would be prime. Riddled with quasars, this constellation has got to produce some amazing things! Have a look at a quasar for yourself tonight. You'll find 0839+187 about half a degree away from Delta Cancri. 0851+202 lies two degrees northeast and 3C215 is five degrees east-southeast. 3C212 and 3C208 are within two degrees north of Alpha, and are less than a degree apart, with radio source 3C208.1 in between them! While they will appear as nothing more than stellar nicks, these are quite probably our only visual point of reference for the black holes at their hearts.

While you're out, watch for bright streaks belonging to the Delta Draconid meteor shower. Its radiant is near the Cepheus border. The fall rate is quite low with around 5 meteors per hour and your best chance is before the Moon rises!

Sunday, April 8 - With very little time before the Moon rises tonight, let's begin a new adventure as we move into the constellation of Cancer. This will be an ideal time to familiarize yourself with its dim stars and one very bright open cluster. Try using both Pollux and Procyon to form the base of an imaginary triangle. Now aim your binoculars or finderscope near the point of the apex to discover M44 - the Beehive (Right Ascension: 8 :40.1 - Declination: +19 : 59).

According to ancient lore, this group of stars (often called the Praesepe) foretold a coming storm if it was not visible in otherwise clear skies. Of course, this came from a time when combating light pollution meant asking your neighbors to dim their candles. But, once you learn where it's at, it can be spotted unaided even from suburban settings. Hipparchus called it the "Little Cloud," but not until the early 1600s was its stellar nature revealed.

Believed to be about 550 light-years away, this awesome cluster consists of hundreds of members - with at least four orange giants and five white dwarfs. M44's age is similar to that of the Pleiades, and it is believed that both clusters have a common origin. Although you won't see any nebulosity in the Beehive, even the very smallest of binoculars will reveal a swarm of bright stars and large telescopes can resolve down to 350 faint stars.

For those of you who use only your eyes to observe - look again at the Beehive and concentrate on Delta to the southeast. Known as Asellus Australis, this is a yellow optical double star often called the "southern donkey." Need more? Then check out Mars’ position not far from Alpha Leonis – and just a few short degrees away from the impressive “Leo Trio” galaxy field. Capture them tonight!

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

Written by Tammy Plotner. Image: Aurora Australis - Credit: Shevill Mathers, Southern Cross Observatory, Tasmania 42 South

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