Most stars you see in the night sky are actually made up of multiple stars – in fact, about 85% of stars are made up of at least two star systems (binary star) and many more are made up of multiple star systems having three or more stars.
In multiple star systems, the members of the system are often very close to one another, making visual observations impossible. Astronomers use various methods for detecting these types of systems, including spectroscopy, occultation, and anomalies in their proper motion (parallax). While these types of multiple star systems are common, there are also multiple star systems in which you can discern the individual members – these types of systems are called visual doubles.
Here’s an example of a visual star system:
There are two members of this system: Albireo, the orange star, and Beta Cygni, the blue star. This is possibly one of the most popular and beautiful double star systems. The separation between the two stars is about 35 arcseconds.
What is interesting about this pair is that it is not a physical binary system, meaning that the stars are not physically interacting with one another – they just appear to be close to one another due to our line of sight from Earth. Albireo is 434 light years from us and Beta Cygni is 401 light years from us and in all the years that we have been observing them, the stars have not moved with respect to one another which indicates that they are not orbiting one another. It is still an interesting star system to observe. Using Slooh.com, you can schedule a mission using the Slooh 1000 list – simply select double stars and then select Albireo; it is visible from April to November from the Canary Islands observatory.
Here’s another example of a multiple star system:
The primary star of this system is called Epsilon Lyrae and the whole system is made up of 11 members and two of the members are apparent. In reality, the two members are themselves multiple star systems and some observers say they can see some of the members, so this pair has been called a double double. The members of this system are all physically interacting, meaning that they orbit one another.
Here’s another multiple star system, called STT 574 AF:
The image is not as picturesque as the other two yet it does highlight some of the 11 members visible in this system. Like Epsilon Larae, this is a physical multiple star system, so all of the members are orbiting one another.
Finding Multiple Star Systems
There’s a catalog of double stars called the Washington Double Star Catalog and this is the URL to access it:
This is pretty much the gold standard as far as double and multiple stars go, but it’s not very user-friendly. People use the catalog as the basis for their observations, to help identify the members and other details. The problem with this catalog is that it captures all multiple star systems, whether you can actually make out the members or not (and, generally speaking, the members are not visible in a telescope for most of the entries in the catalog).
Fortunately, there are lots of astronomers that are interested in multiple star systems, and many have made available observing lists of interesting multiple star systems. Here’s a listing of some multiple star systems that you can observe using a remote telescope service like Slooh.com, or iTelescope.net (I explain the links are following the table):
| Name | Links | Notes |
| Albireo | Stelle Doppie / Wikipedia | Two apparent members although this is a 15-star system |
| Epsilon Lyrae | Stelle Doppie / Wikipedia | 11-star system with two members easily visible |
| STF 274AB | Stelle Doppie / Image | If you aim for cords RA 19:09:01 Dec: 34:36:00 you’ll get two double stars in the same field of view |
| STT 574 AF | Stelle Doppie / Simbad | 12-star system with 2 members easily apparent; primary is called HD 38 |
| Nu Draconis | Stelle Doppie / Wikipedia | |
| Zeta1 Scorpii | Wikipedia | Not a physical system |
| 32 Comae Berenices | Stelle Doppie / The Sky Live | |
| Delta Cephei | Stelle Doppie / Wikipedia | Very close |
| 16 Cygni | Stelle Doppie / Wikipedia | Almost overlapping but discernable; NGC 6826 is 0.5 deg to the East |
| Psi1 Draconis | Stelle Doppie / Wikipedia | |
| STF 2474 | Stelle Doppie / Stelle Doppie (second member STF 2470) | A pair of multiple systems close to each other |
| NGC 1055 | The Sky Live / APOD Image | A grouping of visual double stars near NGC 1055. The stars are not interacting and just appear together as a result of our line of sight but it is a beautiful grouping |
| Meissa | Wikipedia / Simbad | A non-physical multiple star system; the Simbad image has most of the members in it |
| Regulus | Wikipedia / Stelle Doppie | A multiple star system |
| Acrux | Stelle Doppie / Wikipedia | Close multiple star system |
| Pi1 Gruis and P21 Gruis | Simbad – Pi1 / Simbad p21 | Each star is a binary system and the galaxy IC5201 is 17 arcminutes to the west, so the resulting image is a nice grouping of three objects |
| WDS 00013+0742 DU4 | Stelle Doppie / Simbad (AB members) | Quadruple star system – two pairs plus a fifth all easily resolved; use Aladin to plan your observation of this picturesque system |
| Theta Tauri | Stelle Doppie / Wikipedia | |
| 40 Eridani | Wikipedia | Tripple star system with a binary pair orbiting a central star |
| NGC 7008 | Stelle Doppie | A binary blue and yellow pair below the beautiful planetary nebula NGC 7008. The pair are HD 235422 and TYC 2956-1020-1 |
| Kappa Herculis | Stelle Doppie / Wikipedia | Non-physical double but still a nice pairing |
In most cases, I include a link to Wikipedia about the star. The other links to Stelledoppie.it provides details about the star system, as it appears in the WDS; however, the format is easier to read and aggregates information about all of the members that make up the system.
Using Your Favorite Search Engine
You can find targets on your own by using your favorite search engine and search using a term like binocular double stars, or something similar. Including the term, binocular ensures that the stars have some separation that you’ll be able to observe. Note that not all binocular doubles are interacting – you can research these stars on your own and develop your own observing list.
Understanding the Stelle Doppie Website
Stelle Doppie is Italian for double star. This website is a searchable version of the Washington Double Star catalog. The database also includes data from other star catalogs to make the information more usable. The database lists all members of a multiple star system and has direct links to Simbad to help you with further research.
You can search the database using the names provided in the preceding table, using a star’s name, or the WDS designation. The search result page provides you with a lot of information. At the top is the name of the star system, followed by the coordinates and other details. Here’s an example of the additional details:
18h 44m 20.34s +39° 40′ 12.4″ P.A. 344.20 sep 2.3 mag 5.15,6.10 Sp A4V+F1V dist. 49.78 pc (162.38 l.y.)
Other details include the position angle (344.2), separation (2.3 arcseconds), magnitude (5.15), and distance (162 ly).
Another section follows that has details about observation and notes. The notes section often indicates whether the star system is a physical or visual multiple star system.
The System Components table lists the stars that make up the multiple star system. The SEP column shows the angular separation between the primary member and the member in the table. Clicking the Show link takes you to the details about the star.
When viewing the details about a star, you can click the Go to Simbad link on the left to see more details about the star you’re reviewing. This information is helpful if you’d like to look at the star in something like the Aladin Sky Atlas before you schedule a mission to observe, which I highly recommend because you’ll be able to get an idea of what the star system looks like before going to the trouble to observe it (I discuss using Aladin in this article).
Journal of Double Star Observations
There’s a journal that regularly publishes articles about double stars – research and other details. The journal can be a good source of finding double stars of interest:
Conclusion
In this article, you learned about double and multiple star systems, you learned about the differences between types of systems, you saw some images of multiple star systems, and you learned about how to find and observe these types of systems.
You must be logged in to post a comment.