Friday, November 8 - Born on this day in 1656, the great Edmund Halley made his mark on history as he became best known for determining the orbital period of the comet which bears his name. English scientist Halley had many talents however, and in 1718 discovered that what were referred to as "fixed stars," actually displayed proper motion. If it were not for Halley, Sir Isaac Newton may have never published his now famous work on the laws of gravity and motion. Tonight let's look towards Cassiopeia as we remember these great astronomers.
Almost everyone is familiar with the legend of Cassiopeia and how the Queen came to be bound in her chair, destined for an eternity to turn over and over in the sky, but did you know that Cassiopeia holds a wealth of double stars and galactic clusters? Seasoned sky watchers have long been familiar with this constellation's many delights, but let's remember that not everyone knows them all, and tonight let's begin our exploration with two of its primary stars.
Looking much like a flattened "W," its southern-most bright star is Alpha. Also known as Schedar, this magnitude 2.2 spectral type K star was once suspected of being a variable, but no changes have been detected in modern times. Binoculars will reveal its orange/yellow coloring, but a telescope is needed to bring out its unique features. In 1781, William Herschel discovered a 9th magnitude companion star and our modern optics easily separate the blue/white component's distance of 63". A second, even fainter companion at 38" is mentioned in the list of double stars and even a third at 14th magnitude was spotted by S.W. Burnham in 1889. All three stars are optical companions only, but make 150 to 200 light-year distant Schedar a delight to view!
Eta Cassiopeiae - Credit: Palomar Observatory, courtesy of Caltech
Just north of Alpha is the next destination for tonight, Eta Cassiopeiae. Discovered by Sir William Herschel in August of 1779, Eta is quite possibly one of the most well-known of binary stars. The 3.5 magnitude primary star is a spectral type G, meaning it has a yellowish color much like our own Sun. It is about 10% larger than Sol and about 25% brighter. The 7.5 magnitude secondary (or B star) is very definitely a K-type: metal poor, and distinctively red. In comparison, it is half the mass of our Sun, crammed into about a quarter of its volume and is around 25 times dimmer. In the eyepiece, the B star will angle off to the northwest, providing a wonderful and colorful look at one of the season's finest!
Saturday, November 9 - Today is the birth date of Carl Sagan. Born in 1934, Sagan was an American planetologist, exobiologist, popularizer of science and astronomy, and novelist. His influential work and enthusiasm inspired us all. If Carl were with us tonight, he would encourage amateurs of every level of astronomical ability. So let us embark to honor his memory with an optical pairing of stars known as Zeta and Chi Ceti, a little more than a fistwidth northeast of bright Beta. Now have a look with binoculars or small scopes because you'll find that each has their own optical companion!
And if you'd like to show your star stuff, then try locating Fomalhaut and drop about a handspan south-southwest into Grus to pick up bright star Beta (RA 22 42 40 Dec -46 53 04).
Zeta and Chi Ceti - Credit: Palomar Observatory, courtesy of Caltech
Around 170 light-years from Planet Earth, Beta Gruis is the 59th brightest star in the sky and the second brightest star not to have a proper name. It's an M-type supergiant, but one that is also slightly irregular - changing by about a third of a magnitude in approximately 37 days. Well evolved, Beta is on its way to becoming a Mira type and is only the size of the orbit of Venus. Its loss of mass could mean it has a dead carbon-oxygen core, and studies at infrared wavelengths point to a shell waiting to be expelled.
In the telescope, you will see Beta also has a visual companion to the south. Although it is unrelated to Beta itself, modern interferometry suggests there may be a true companion star which has yet to be resolved. No matter how you view it, you'll like Beta for its rich color!
As Dr. Sagan would say: "We are all star stuff."
Sunday, November 10 - Tonight we're going to ignore the Moon and head just a little more than a fistwidth west of the westernmost bright star in Cassiopeia to have a look at Delta Cephei (RA 22 29 10.27 Dec +58 24 54.7). This is the most famous of all variable stars and the granddaddy of all Cepheids. Discovered in 1784 by John Goodricke, its changes in magnitude are not due to a revolving companion - but rather the pulsations of the star itself.
Delta Cephei - Credit: Palomar Observatory, courtesy of Caltech
Ranging over almost a full magnitude in 5 days, 8 hours and 48 minutes precisely, Delta's changes can easily be followed by comparing it to nearby Zeta and Epsilon. When it is at its dimmest, it will brighten rapidly in a period of about 36 hours - yet take 4 days to slowly fade again. Take time out of your busy night to watch Delta change and change again. It's only 1000 light-years away, and doesn't even require a telescope. Even binoculars will show its optical companion...
Until next week. Dreams really do come true when you keep on reaching for the stars!
About Tammy Plotner - Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She has received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.