## Constant as the Northern Star

There are frequent astronomical references in the plays of William Shakespeare (1564?-1616).  One famous example is in the tragedy Julius Caesar, written around 1599, where Julius Caesar states,

“I am constant as the northern star,
Of whose true-fix’d and resting quality
There is no fellow in the firmament.”

Little did Shakespeare know that Ejnar Hertzsprung (1873-1967) would discover some 312 years later in 1911 that Polaris, the North Star, actually varies in brightness.  Of course, Shakespeare was referring to Polaris’ proximity to the north celestial pole, but there are multiple ironies in that Polaris varies in brightness—albeit a tiny amount—and it will not always be the “pole star”, thanks to the precession of the Earth’s axis.

Polaris is a classical Cepheid pulsating variable star, with a visual magnitude that has historically ranged as much as 1.9 – 2.1 over a period of about 4 days.

At a distance between 426 and 439 ly, Polaris is the nearest and brightest Cepheid variable star in our night sky. Polaris is a supergiant star (F7Ib) weighing in at about 5.4 solar masses. Polaris and its nearest companion star (F6V, 1.3 solar masses) enjoy a complete orbital pas de deux every 30 years.

Currently, Polaris lies only 40 arcminutes from the north celestial pole (declination +89° 20′).  As with all stars, the Earth’s rotation causes the stars to wheel around the celestial poles, although in the case of Polaris the angular speed is exceedingly slow, making it a great target for a telescope without a clock drive.

Let’s figure out how fast glacial Polaris moves. It traverses a tiny circle around the north celestial pole every sidereal day (23h56m04s), so what is its angular speed?  We need only divide the path length (the circumference of a circle of radius 40′) in arcseconds by the number of seconds in a sidereal day to get the angular speed in arcseconds per second of time. The circumference of a circle is 2πr, so plugging and chugging we get [(2)(3.141592654)(40*60)] / 86164 = 0.18 arcsecond per second of time. Sound like a lot, or a little?  This angular speed means that Polaris moves an arcsecond every 5.7 seconds, or 11 arcseconds every minute, or 11 arcminutes every hour. That’s just 4.2° per day.

Not quite a perfect pole star, but it will certainly deux.

## A New Chapter

After nearly 20 years of putting together a weekly sky/space/history events calendar, I am calling it quits.  Why?  It takes a huge amount of my time, and keeps me from doing a lot of other things.  Even though I believe it to be the most comprehensive astronomy calendar in existence, I am 60 years old now, what I do for a living is more demanding of my time and energy than ever before, and I want to do more reading, more writing, more getting involved in the community.  Life is short and you start thinking about all the things left to do when you hit the big 6-0.

Besides, I’m not sure that many people use the calendar on a regular basis.  For one thing, many of the event times are for a specific location.  Dodgeville is a small town with very few people interested in astronomy (ironic, isn’t it?).  These factors alone would discourage a wide readership.  Such a location-specific calendar would make more sense in an astronomy-oriented community such as Mirador Astronomy Village which I would love to help develop but will never have the resources to start.

One thing that will not change is the article portion of my weekly column.  These will now be separate journal entries, and I will have the flexibility to post as often as time allows rather than on a rigid once-a-week schedule.  I expect that the quality of these postings will actually improve since I will be able to devote more time to them.  And you, the reader, will have the opportunity to comment, question, and contribute additional information.  That is a good thing!  Finally, in the past, I dropped my articles off the web after seven weeks.  I’d like to think that some of what I write is worth keeping around longer than that.

So, here we go!