Xi Scorpii

The otherwise visibly unremarkable star Xi Scorpii is in truth a set of five, two pairs traveling together and a fifth member orbiting one of those.

Many of the stars that we perceive as solitary points of light easily resolve into pairs and sets when viewed with a modest telescope. Some naked-eye interest in the night sky reveals the pair Alioth-Mizar in the middle of the Handle of the Big Dipper. Medieval astronomers knew the Beehive Cluster of 1000 stars as the Manger of seven stars, just as the Pleiades (also about 1000 stars) were the Seven Sisters to the ancient Greeks (among very many other traditions). The invention of the telescope and the advent of micrometrical recording expanded our understanding of space and time: some arrangements are accidental to our point of view; others move together temporarily locked into association by gravity. Amateur astronomers call them all “binary stars” and many are true pairs. The term also includes larger sets such as Xi Scorpii. 

 

After a first view on 19 June 2022 at 0038, 
I returned that night at 2357

I found Xi Scorpii from a new book by Agnes Clarke, Discovering Double Stars: Double Stars for Light-Polluted Skies (Transtextual Books, 2022). I met Clarke on the Cloudy Nights discussion board. They are listed by their Struve numbers STF 1998 and STF 1999 in An Anthology of Visual Double Stars by Argyle, Swan, and James (Cambridge, 2019). Being self-published on demand through a contractor, Clarke’s book is frequently updated. The Cambridge volume provides more astronomical and astrophysical data for each listing.

Earler in the week, I was working with the Celestron AVX computerized “goto” mount and tripod carrying an Explore Scientific 102mm achromatic refractor. However, for this, I used a 130mm reflector from Astronomers Without Borders and the ES102mm on manual mounts. 

I started at dusk, as soon as I could align the red-dot finders on Spica. I just kept checking stars for the familiar pattern. I refered to the Sky & Telescope Pocket Atlas to check my bearings relative to Yed Posteriori and Yed Priori in Ophiucus

 

Discovering Double Stars by Agnes Clarke.
She uses 5x and 8x finder scopes for measuring.

The easily visible pair has a period of only 44.5 years. They are about 2.7 billion km apart about the same as the distance from the Sun to Uranus. The fifth member of the set takes 1514.3 years to orbit them. 

The other pair is designated Struve 1999 and was originally considered separate but in modern times was computed to be traveling with the other three. They orbit so slowly – hence at a great physical distance –that no discernable change has been noted. The entire family is about 80 to 90 light years from us. According to the SIMBAD database they are coming to us at 36.33 km/sec (Burnham gave 20 mi/sec). So, we have about 700,000 years to make plans. 

 

From Argyle, Swan, and James.
The stars are near maximum separation.

The close pair AB are both subgiant F5 IV stars on the Hertzsprung Russell Diagram: OBAFGKM. They are on the main sequence, fusing hydrogen. Their temperatures are about 6700 kelvins (the Sun is 5,778 K) and they are about 2.4 times more luminous than the Sun. Metals are present. 

 

The wider pair are K-types, dK0 and dK3, meaning that they are dwarfs, smaller and cooler than the Sun. K0 mass 0.88 suns and 5270 K while K3 are smaller 0.78 suns and 4830 K. They are classified as orange though they did not appear so to me in either my 130mm reflector or my 102mm refractor over two different nights.

(What's funny about this is that I just wrote an article about Scorpius X-1 the first discovered stellar x-ray source. So, it has a symmetry:  ex-one, ex-eye.)

 

Previously on Necessary Facts

Parallax: The Race to Measure the Cosmos 

Copernicus on the Revolution of Heavenly Bodies 

Astronomy 

Jupiter-Mars Conjunction

M44 the Beehive Cluster 

Jupiter-Saturn Conjunction 

Viewing Mars

Binary Stat Project

A Good Night Observing

Recent Astronomical Observing 

Messier 13: The Hercules Cluster

Last night, I learned how to find the Hercules Cluster. I selected Messier 13 from a menu on a Celestron AVX computerized telescope mount, and in a 102mm refractor I viewed it at 47x. I then spotted it in the red-dot finder scope. From there, I went to a 130mm reflector mounted on a manual drive and placed that red-dot finder in about the same location. And with the same 14mm ocular there it was at 46x, not noticeably smaller and yet a little brighter in the larger aperture. 

Taken with the NASA Harvard 6-inch
Maksutov f/3.47

 An active amateur astronomer will tell you that it is easy to locate this huge sphere of stars. It is nominally a summer constellation near the zenith when the sky is finally dark from mid-June to mid-July though rising with nightfall from April and May and setting at sundown in October and November. That is nice to know. 

Midnight 18 June
(Philip's Planisphere Octopus Publishing
and Cambridge University Press 
(part of a set found at Half Price Books).

 

The fact remains that only four constellations look anything like what they are named for: Scorpius, Leo, Orion, and Taurus. We tell extended and involved stories about the others to help us remember them because otherwise they are just a dense random scattering of small lights. From the city, they are a thin random scattering. I once read that the southern sky is so dense with stars, including the lesser galaxies that we call the Magellanic clouds, that the Incas noted the dark lanes as more interesting. 

 

The stars are pretty at any magnification. I like to understand what I am looking at. Burnham’s Celestial Handbook provides four pages of history and explanation on M13 as an introduction to another four pages about globular clusters in general. 

 

 Octopus Publishing
and Cambridge University Press 
(part of a set found at Half Price Books). 

They orbit above the pinwheel disk of our galaxy and are “extremely ancient.” William Herschel estimated 14000 stars in the Hercules cluster. A hundred years later, Mount Wilson doubled the estimate. But the central core is so dense that Burnham suggests one million stars as the upper limit. 

 

The Virial Theorem lecture from the École
polytechnique fédérale de Lausanne and edX

Newton’s powerful mathematics fails with three bodies. Modeling an extra-galactic globular cluster of stars works best by considering them as point masses in a gas cloud. The Virial Theorem allows us to analyze them from considerations of the temperature of a gas. That also works from the considerations of kinetic versus potential energy as the stars move about their common center of mass. 

 

PREVIOUSLY ON NECESSARY FACTS

 

An Online Class in Astrophysics 

In Suspect Terrain 

The Map that Changed the World 

Observing with NASA: A Platform for Citizen Science 

(Not) Observing with NASA and Harvard 

The Whole Nine Yards

We bought this home in December 2021 in part because of the above-ground swimming pool. As it turned out, we bought a pig in a poke. The pool had holes in it and was not laid in correctly. We took it down and dug a new foundation. We started about ten weeks ago and it is a work in progress.

We thought that we could to the work ourselves, a little at time each night.

At first, I was reminded of Alice's Retaurant
with its shovels and rakes and implements of destruction.

Soon enough, however, I was thinking more of
The Bridge on the River Kwai.

We got help, hiring two neighborhood guys,
one in high school, the other in college.

Then we had the sand delivered for the new foundation.
The sand was a lot easier to transfer than the work
to bust the sod.

 I had the guys come back for about
90 minutes each and did the last eight hours myself.

The new pool has been delivered. We still have to set the foundation. I figure that setting up the pool will be easy until the last section needs to be tensioned and secured. We have tiles for the footings and barriers for the edging. Mostly, we have a will to succeed and helpful neighbors looking for work.

PREVIOUSLY ON NECESSARY FACTS

CITIES 

EPIGENETICS

ALONGSIDE NIGHT TO RUN IN AUSTIN

BRINGING PHILOSOPHY TO ATHENS: ASPASIA OF MILETOS