The Monthly Sky for October 2016
Planets low, Algol dims, Albireo great!
by Viktor Zsohar
The Monthly Sky has returned, because the Yukon is blessed again with longer and longer nights during the winter months. Members of the RASC: Yukon Centre have started to take advantage of the clear and dark skies that October had and has yet to offer.
OCTOBER YUKON SKY EVENTS
Oct 1 New Moon
Oct 2 Algol at minimum
Oct 3 Mars at greatest heliocentric latitude South. Venus 5 degrees South of Moon.
Oct 4 Moon at apogee
Oct 5 Algol at minimum
Oct 8 Mercury at greatest heliocentric latitude North. Draconid meteors peak. Pallas stationary. Algol at minimum
Oct 9 First quarter
Oct 11 Mercury 0.9 degrees of Jupiter (in daylight) Algol at minimum
Oct 13 Neptune 1.2 degrees South of Moon, occultation!
Oct 14 Algol at minimum. Algol’s minimum brightness is magnitude 3.4 compared to its usual 2.1, for roughly two hours, centered on 1:00 a.m. EDT; 10:00 p.m. PDT. At any random time you glance up at Algol, you have a 1-in-30 chance of catching it at least 1 magnitude fainter than normal.
Oct 15 Uranus at opposition
Oct 16 Full Moon
Oct 17 Moon at perigee. Large Tides between 17th and 20th of the month
Oct 19 Aldebaran 0.3 degrees South of Moon. No occultation in the Yukon
Oct 21 Orionid meteors peak. Ceres at opposition
Oct 22 Algol at minimum. Last Quarter
Oct 25 Algol at minimum. Regulus 1.6 degrees North of Moon
Oct 27 Mercury in superior conjunction
Oct 28 Algol at minimum. Jupiter 1.4 degrees South of Moon
Oct 29 Mars at perihelion
Oct 30 New Moon. Saturn 3 degrees North of Venus, group with Antares
Oct 31 Algol at minimum. Moon at apogee. Venus at aphelion
PLANETS IN OCTOBER, 2016
Mercury is well placed in the morning sky in the first part of the Month, then not visible from the Yukon for the rest of the Month. In daytime conjunction with Jupiter on the 11th. In superior conjunction with the Sun on the 27th.
Venus sets just after the Sun, but Yukoners with a good SW Horizon access will be able to observe the dance of the shining Venus with Saturn during the second part of the Month. Aphelion is on October 31st.
Mars is in Sagittarius, positioned very low above Yukon Horizons towards South-SouthWest. It is visible between around 7pm to 9pm. It’s brightness is about +0.1m, such as Vega.
Jupiter reappears in the eastern dawn twilight in Virgo by mid-month. As the planet rises earlier each day, it starts to rule the starry winter skies of the Yukon.
The Ring Planet is still visible in October. While pairing up for a dance with Venus, Saturn will appear lower and lower above the SW Horizon, then disappears in the dusk for the rest of the winter.
Uranus is at opposition on the 15th in Constellation Pisces, and visible all night long. It sits about 37 degrees above horizon, therefore it is well-placed for observation with binoculars and telescopes. Its visual magnitude is +5.7m, theoretically a naked-eye object under clear dark skies.
Neptune is visible most of the night. It is retrograding in Constellation Aquarius. Visual magnitude is +7.8m, thus observable with binoculars and telescopes.
DEEP-SKY OBSERVATION GUIDE
OBSERVE ALGOL AND ALBIREO
Variable stars are stars whose brightness changes on timescales from minutes to years. they reveal many stellar properties. Depending upon their type, variables can tell us their age, mass, radius, temperature, luminosity, internal and external structure, composition and evolutionary history. Systematic observation of variable stars is an area where amateur astronomers can make a valuable contribution to astronomy. (Observer’s Handbook, p. 298)
Double and multiple stars make up about 85% of stars found in our Milky Way Galaxy. While the first detection of double systems dates back to the 17th century, it was not until the systematic work of Sir William Herschel, the physical nature of these systems were ascertained. The larger the aperture of the telescope, the closer the stars that can be separated under good sky conditions. The resolving power of your telescope can be calculated as 120/D, where D is the diameter of the telescope objective or mirror in millimeters. Professional astronomers using long-baseline optical interferometry to measure double-star separations less than a milliarcsecond (0.001″).
What’s the scariest star in all the heavens? If you were one of the early stargazers, you might have chosen Algol in the Constellation Perseus. Early astronomers nicknamed Algol the Demon Star. Of course, like all stars, Algol isn’t the least bit scary. But it’s associated in skylore with a mythical scary monster – the Gorgon Medusa – who had snakes instead of hair. It’s said that she was so horrifying in appearance that the sight of her would turn an onlooker to stone.
The star Algol takes its name from an Arabic word meaning “the Demon’s Head”. This star is said to depict the terrifying snake-y head of the Medusa monster. In the mythology of the skies, Perseus – a great hero often depicted mounted on Pegasus the Flying Horse – used Medusa’s head to his own advantage – to turn Cetus the Sea-monster into stone. Perhaps the ancients associated this star’s variable brightness with the evil, winking eye of the Medusa.
Winking? Yes. Algol is a known variable star, which waxes and wanes in brightness. There are many variable stars known throughout the heavens, but Algol might well be the most famous variable star of them all. This star brightens and dims with clockwork regularity, completing one cycle in 2 days 20 hours and 49 minutes.
Moreover, this variable star is easy to observe with just the unaided eye. At its brightest, Algol shines about three times more brightly than at its faintest. At maximum brilliance, Algol matches the brightness of the nearby second-magnitude star Almach. At minimum, Algol’s light output fades to that of the star Epsilon Persei.
Modern-day astronomy has unlocked the secret of Algol’s mood swings. It’s an eclipsing binary star. This kind of binary is composed of two stars, with each star revolving around the other. From Earth, we see the orbital plane of this binary star almost exactly edge-on. Therefore, when the dimmer of the two stars swings in front of the brighter star, we see Algol at minimum brightness. In conclusion, Algol is a variable star because it is a double-star system. There are, however, variable stars that change brightness over a period of time for other reasons, and we will unlock some of the secrets of the variable stars in the November issue of Monthly Sky.
Albireo is known best for the striking color contrast between its two stars, with the brighter star gold and the dimmer star blue. Albireo – also called Beta Cygni – isn’t the brightest star in the sky. It looks like an ordinary single star to the eye. But peer at it through a telescope, you’ll learn why stargazers love Albireo. With a telescope, you’ll easily see Albireo as a beautiful double star, with the brighter star gold and the dimmer star blue.
How can you see Albireo as two stars? They are best viewed at 30X (“30 power” or a magnification of 30). Unless you have exceedingly powerful binoculars, mounted on a tripod, binoculars won’t show you Albireo as two stars, but any small telescope will. When you do see Albireo as two stars, notice the striking color contrast between the two.
How can you spot Albireo in the night sky? It’s easy to find, if you can locate Cygnus the Swan. Cygnus has an easy-to-recognize shape, that of a cross, and the constellation is also known as the Northern Cross. The brightest star in Cygnus, called Deneb, marks the head of the Cross or the Tail of the Swan. Albireo marks the base of the Cross or the Head of Cygnus.
The two stars of Albireo constitute a true binary star system. In other words, its two stars aren’t merely a chance alignment as seen from Earth. Instead, they revolve around a common center of mass.
These two stars lie quite far apart, however, and might take as long as 100,000 years to orbit one another. Even though these two stars appear close together in a telescope, keep in mind that you’re looking at a system that’s 430 light-years away.
By the way, the brighter of the two stars in the Albireo system has been found with advanced telescopic techniques to be two stars as well. Thus there are at least three stars in this system. Bottom line: The star Albireo in the constellation Cygnus – also known as Beta Cygni – is a famous double star. A small telescope reveals that one star is blue and the other is gold.
DID YOU KNOW?
YOU CAN OBSERVE ALGOL AND ALBIREO WHILE TAKING THE
EXPLORE THE UNIVERSE CERTIFICATE PROGRAM!
IT IS AVAILABLE FOR DOWNLOAD AT
If you want to learn how to observe celestial objects and what to observe in the sky, we invite you to challenge yourself by completing this program, either observing alone or together with us! We will start the certification program during our next observation session, while Maurice is already way ahead of us! Viktor will inform you by the “Remind” texting system as usual for observation announcements.
- 2016 RASC Observer’s Handbook
- Algol is the Demon Star. Bruce McClure in Brightest Stars | October 31, 2014 at earthsky.org
- Starry Nights Pro7 Software
- Albireo, beloved double star. Bruce McClure in Brightest Stars | August 3, 2016 at earthsky.org