…continuedObserving Double Stars for Fun and Science
A Night at the Telescope
With the preliminary adjustments out of the way, you're all set to begin making double-star measurements. The pair being measured should be at least 30° above the horizon to reduce differential refraction and well within the magnitude and resolution limits of your telescope. Begin by locating your first pair and boosting the magnification until the stars span as many reticle divisions as practical. The method I find best for measuring separation with the Microguide reticle micrometer is to carefully rotate the eyepiece until the primary and secondary stars are parallel to the linear scale and the primary is dead center on one of the scale's divisions. Estimate the separation of the pair to 1/10 of a division and convert this into arcseconds using the calibration value for the setup. That's all there is to it you have just measured the star's separation.
Before you start celebrating, keep in mind that there is a second equally important measurement to make: the position angle of the pair. Begin by rotating the eyepiece until one of the reticle lines of the linear scale bisects both the primary and the secondary at the same time. Now is a good time to note the approximate position-angle reading on the degree scale. This will serve as a reality check to ensure that you haven't made a mistake and that your position angle is near the expected value for the stars being measured.
When you are confident the reticle is correctly positioned, take an accurate reading off the degree circle. Then rotate the reticle 180° and repeat the reading. This procedure is done again for a total of four readings. The results are averaged (remember to subtract 180° from the readings obtained by rotating the reticle). Keep in mind that when the primary star is centered in the field of view, the companion is said to have a position angle of 0° if it is directly to the north of the primary, 90° when directly east, 180° when directly south, and 270° when directly west. Be careful to avoid accidentally offsetting your measurement by 90° or 180°. This is where your reality check comes into play. For greatest accuracy, the measurements of separation and position angle should be repeated on four to six nights and the results averaged.
|13 Neglected Double-Star Systems|
|MLB 639||04h01.1m||+27° 33'||8.7||10.3||267°||7.3"||1930|
|COU 3244||05h00.0m||+32° 44'||9.8||13.5||87°||2.9"||1973|
|HDS 817||06h00.1m||+51° 26'||8.7||11.9||251°||17.0"||1991|
|POU 2367||07h04.2m||+23° 24'||7.6||12.9||166°||27.2"||1907|
|HJ 453||08h38.6m||+34° 29'||9.0||14.3||102°||19.0"||1903|
|BAL 2368||09h52.2m||+03° 13'||8.9||9.9||37°||13.2"||1910|
|HEI 354||10h03.7m||+06° 00'||9.5||13.5||340°||3.6"||1988|
|LDS 3032||11h16.1m||+54° 14'||9.6||19.8||318°||18"||1960|
|VYS 5||12h12.3m||+54° 29'||9.8||13.3||0°||15"||1966|
|STF 1745||13h20.3m||+79° 26'||9.3||11.6||200°||20.3"||1905|
|ES 1085||14h16.5m||+46° 33'||8.8||11.8||172°||6.1"||1911|
|KZA 80||15h20.7m||+31° 33'||9.5||10.0||54°||26.8"||1984|
|AG 348||16h00.2m||+14° 11'||9.5||10.0||26°||16.3"||1893|
|The double stars listed here have only a single published measure each. That measure and the date of it are provided. What has happened since is anybodys guess. Some of the observations are quite recent while others are very old. All the doubles are challenging.|