Double Stars

The Double Stars Program

sketch of double star Gamma HerculisWelcome to the RASC Double Stars Observing Program. It encourages observers to view a variety of doubles and multi-star systems. As noted in the Observer's Handbook, 85% of stars are doubles or triples. This program is aimed at the intermediate visual observer. RASC members who complete the program may apply for a certificate.

This program will:

  • Nurture interest in double stars.
  • Present an array of interesting double stars.
  • Reinforce good observing practices and techniques.
  • Encourage active observing programs in RASC Centres.

The Double Stars Observing Program may be completed with a small telescope. Using different magnifications is recommended.

Observers may enjoy viewing from urban locales, and during periods with a bright Moon, as double stars can generally be viewed from anywhere and any time. While dark adaptation is helpful, a dark site is not a requirement. Atmospheric seeing can impact double star viewing.


Program Details

The 110 double star targets are visible from the northern hemisphere in many constellations. The list should present few difficulties for observers between north latitudes 40 to 50. The program can be started at any time and can be easily completed within 12 months.

Typical double star lists show separation, position angle, colours, and magnitudes. The RASC double stars program departs from this convention to help observers view targets without preconceptions. With only coordinates and combined brightness, it allows the observer to “discover” the nature of the double star on their own without any bias. 

If the observer prefers to know in advance the details of each target double, they may use the detailed Supplementary list.

A certificate will be awarded to a RASC member who visually observes all 110 pairs on the official Double Stars Observing Program list as published.


Program Requirements

We recommend observers read the Double Stars Program Guide. This 12-page guide includes examples of both textual observing notes and representative sketches, examples of what you might see, and how to best present your log notes in order to earn the certificate. Suggested terminology is provided.

For people in a hurry, we offer a Quick Start Guide.

You may download and complete our partly filled-in log book with target names and aliases. Alternatively, you can use your own notebook. If using your own log books or sheets, review our forms so as ensure you capture the necessary information. We expect detailed indications of what you saw. 

Briefly, for each double star, document your impressions. Does it look like a double or a triple? Describe the main pair of stars, their distance from each other and angle in the eyepiece. Observe the colour and brightness of each star. Optionally, include a simple sketch.

Obtain our double stars checklist. You can download the main list in a variety of formats, including SkySafari and Excel. You can then start recording your observations. 

Again, the main checklist file does not show separation, position angle, colours, and individual magnitudes so to allows the observer to “discover” the nature of the double star. However, if the observer prefers to know in advance the details of each target double, we offer at the Supplementary list.

The program may completed by traditional star-hopping or with computer assistance or a GoTo telescope. 

Do not email large files or multiple files to the Observing Committee chair. Ask about our new Uploader Service!


Let's Split Doubles!

Ready to get started? Download the full guide, log book (or single sheet), and the main checklist. Access other materials as needed. See below.

Software observing list files are provided.

  • SkyTools observing list .STX (after downloading, remove the .DOC extension)
  • SkySafari observing list .SKYLIST (after downloading, remove the .TXT extension)
  • editable Excel workbook .XLSX files

This Observing Program is designed to be an INDIVIDUAL EFFORT. When you complete the program and apply for your certificate, you will have met these requirements: you located the object yourself, made your own observation at the eyepiece, kept your own log book or pre-programmed observing forms, and then applied for your certificate on your own merit. Enjoy your journey through this program!

Use the generic application form (PDF, 185 KB) for this visual certificate application. The form has a language of choice option for the Certificate. Indicate your home affiliated RASC centre or "National" or "Unattached" if not associated with a specific centre.


Program Feedback

Version 1.0 of the RASC Double Stars Observing Program was launched in October 2020.

The Observing Committee has rigorously checked the content of this certificate program to make it as accurate and complete as possible but there may be issues, errors, or omissions. 

Contact the Observing Committee Chair [observing AT] if you have any questions or comments about this or our other certificate programs.


Double Stars Resources

See the RASC Observer's Handbook for its two essays: DOUBLE AND MULTIPLE STARS by Brian Mason and COLOURED DOUBLE STARS (with addendum) by Michel Duval.

Sissy Haas authored the popular Double Stars for Small Telescopes with over 2100 targets. Published by Sky and Telescope.

Serious observers should acquire the technical book Observing and Measuring Visual Double Stars, second edition, by R.W. Argyle. Published by Springer.

Professionals, amateurs, and students regularly produce reports and papers on double stars and multi-star systems. Many of these are made available through the Journal of Double Star Observers.

Note eyepiece magnifications in your double star observing notes. See the Sky & Telescope web site for their online calculation tool.

There is much activity on the Cloudy Nights Double Star Observing online forum.

See the excellent Double Star Astronomy section in Bruce MacEvoy's web site. He discusses getting started, how to "train" your eye, star colours, etc. He co-produced the second edition of the Cambridge Double Star Atlas.

The official source for doubles is the Washington Double Star (WDS) catalogue. As of October 2020, it warehoused over 150 000 pairs. Managed by the US Naval Office, the database is currently hosted at the Georgia State University web site.

And don't forget to peruse our Observing Tips and Expectations page...

Observing (bookmark) list files for Stellarium are available at the RASC Toronto Centre web site.


Change Log

23 Feb 2021 - Blake Nancarrow. Hugues Lacombe spotted an issue with Mintaka. Washington Double Star reference BU 558 specifically refers to extremely challenging AB pair. The easy target AC pair is referred to as STFA 14. The main checklist PDF and Excel files were updated accordingly as well as the log book.

27 Mar 2021 - Blake Nancarrow. A request was made by Chris Vaughan and Nick Pierre to show the constellation code on the supplement list. The PDF was update to include a constellation designated. A number of other minor updates were also applied.

11 Apr 2021 - Blake Nancarrow. Many updated files plus added a new "bookmark" JSON file for Stellarium.

10 Jul 2021 - Blake Nancarrow. Many updates. New main checklist PDF and XLS. New supplemental PDF. More star colours added. Errors in directions corrected. Cardinal directions with degrees infographics added. Thank you Chris Vaughan and Melody Hamilton for feedback.