By Bill Pellerin

Houston Astronomical Society

GuideStar Editor

Amateur astronomy can get confusing, and for lots of reasons. Keeping up with who discovered what, how he or she named it, what it really is, and whether you can observe or image it is enough to make your head spin. So it is with the Struve family and the double stars that carry their name.

The Struve family had a lot of family members involved in astronomy for several generations from (1755 to 1992). Trying to sort through all the accomplishments of this family can be a challenge, so to keep it manageable we’ll focus on their work cataloging double stars. There are two members of the family we normally associate with double stars, Friedrich Georg Wilhelm (von) Struve (1793-1864) and Otto Wilhelm Struve (1819-1905) the son of FGW Struve.

FGW Struve lived in Europe his entire life and became a professor of astronomy at what was then known as Dorpat University in Estonia. While there he measured the position of double stars with a micrometer and published his ‘Catalog of New Double Stars’ in 1827.

Otto Wilhelm Struve was the head of the Pulkovo Observatory (Russia) until 1889. Otto continued the work of his father and has his own catalog of double stars — smaller than his father’s.

These are the Struve family members most associated with double stars. It is worth noting that a grandson of Otto Wilhelm Struve, also named Otto Stuve (they named him Otto to confuse us) lived from 1897-1963 and was the director of the Yerkes Observatory in Wisconsin and the McDonald Observatory in Texas. His PhD work was on spectroscopic double stars and was done at the University of Chicago. He does not appear to be a significant cataloger of double stars, however.

How to Find These Stars….

Six of the stars in the Astronomical League’s Double Star observing club have the designation Struve attached to them. Five are connected to the elder Struve and one is associated with Otto Struve. This is an excellent observing program. The objects are generally easy to see and often visually stunning. I completed the list in 1999, and I highly recommend it.

Here’s where observing the Struve stars can get complicated. The FGW Struve catalog of double stars is often designated with a sigma (Greek character) and then a number (example: Σ2470), but not always. The Otto Struve catalog double stars have the letter ‘O’, then the sigma character and then a number (example: OΣ123).

The famous Washington Double Star catalog (WDS) identifies double stars as WDS <ra_dec> (http://ad.usno.navy.mil/wds/). So, for the double star we’ve been using as an example (Σ2470), the WDS designation is WDS19088+3446, which means the star is at RA 19 deg 08.8 min / Dec +34 degrees 46 min. Since that double star was cataloged by Fredrich Georg Wilhelm Struve, the three-letter-identifier of the discoverer in the WDS catalog is STF (remember Struve The Father). You can find this star pair in the WDS catalog by looking for the text ‘STF2470’.

A double star in the WDS catalog that was discovered and cataloged by Otto Struve uses the identifier STT in the ‘discoverer’ column followed by the Otto Struve catalog number. You can import the catalog into a spreadsheet, parse the rows, and filter the list to see only the WDS stars that were discovered by STF or STT. Or, you can search the list for your star pair of interest using a search string such as ‘STF2470’.

When you filter the WDS catalog, you’ll find that 4394 double stars in the WDS catalog were discovered by FGW Struve and 996 star pairs in the catalog credit Otto Struve as the discoverer. (Note that the full WDS catalog has 118,444 entries.)

In TheSky (Software Bisque) you can find the FGW Struve stars as ‘Struve 2470’ or ‘WDS STF2470’ and the Otto Struve stars as ‘WDS STT123’. In SkyTools (Skyhound) the FGW Struve double stars are found using the ‘STF2470’ format and the Otto Struve double stars are found using the ‘STT123’ format.

An Observing Exercise

Finally, here is an easy observing exercise for you – one which allows you to see a pair of FGW Struve’s double stars in the same field of view (I found this in the book A Year of the Stars by Fred Schaff). These stars make up another double-double (similar to Epsilon Lyr) in Lyra and are worth the effort to find.

To find Struve 2470 / 2474 (also known as SAO 67870 and 67879) point your telescope at RA 19 h 08 m 56 sec and Dec 34 deg 40 min 36 sec — the approximate midpoint of the two star pairs. These stars are around 7^th to 8^th magnitude, so they are quite a bit dimmer than Epsilon Lyr.