Spath Blade Double Image Micrometer

Double-image micrometers generate two images from one incident light source. Instead of setting an external device - like in the filar micrometer - with respect to the object to be measured, the two images with equal brightness are oriented with respect to each other to measure position angle and distance. The first construction was introduced by P. Muller 1 he used a birefringent quartz glass crystal. Figure 13.1 shows the orientation of the crystal axes, the incident ray i and the ordinary...

Computer Databases

Before discussing computer star charts it worth looking at the raw data itself. Most computer star charting programs use the raw data from the Washington Double Star Catalogue, or WDS for short. This database which is updated daily with new measures and recently discovered double stars is maintained by the United States naval Observatory and is available through the Internet at http ad.usno. navy.mil wds wds.html. This site includes the database itself which can be downloaded, although at the...

Computer Star Charts

Computer star charting programs come in two different flavours the multimedia directed ones such as Redshift 4 and Starry Night and the observer orientated ones such as SkyMap Pro, Guide, Megastar and The Sky. Neither Redshift 4 nor Starry Night Deluxe appeared to have any double star information at all. Even if you click on a bright double star such as gamma Andromedae nothing comes up to indicate its multiple nature. These programs are more aimed at the educational market than the observers'...

New Zealand

In the southern hemisphere, very few observers are active, even though there are many underobserved systems. One exception is Ormond Warren whose interest began in primary school when the headmaster allowed him to use his 3-inch refractor. In 1987 he became interested in double star astronomy after moving to Wanganui, where he found the city observatory had a fine history in this field. His first study was the set of pairs and triples originally discovered at this site, early last century, and...

Does the Sun have a Companion

As we have seen the Sun is, as a single star, apparently in a minority amongst the stars in the local neighbour- Notes on double and multiple stars within 5 Proxima Cen V645 Cen variable 0.01m a Cen A a 17'.' 515, P 79.920 yr Eri dust ring planetary companion Wolf 424 V(AB) 12.44, Am -0.01. IL Aqr 2 planetary companions P 30.1 and WX UMa sep(AB) 28, PA 133 D Leo resolved by speckle ( ) Heintz no hood. As more very faint companions to nearby stars are found this will make it even more unusual,...

The Chronometrie Method

The chronometric method allows a significant increase in accuracy over the ring method. Of comparable antiquity, it requires the addition to the telescope of an external position circle or dial, as well as a single wire or thread mounted at the focus of the optical system. A motor-driven mount is, if not an absolute necessity, at any rate highly desirable. Since position angles are measured directly with the circle, the chronometric method is a hybrid technique rather than a pure transit...

The Dawes Limit

Dawes arrived at this relationship in 1867 after tests with a large number of apertures over a number of years. Unfortunately, Dawes only had the experience of refracting telescopes and was not able to comment on the application of this relationship to reflectors, let alone modern catadioptric telescopes In the next chapter, Christopher Taylor will argue that the Dawes limit applies equally to reflectors at least to apertures of 30 cm. Although the Dawes limit is an empirical limit which...

France

France has always been a centre of excellence for double star studies. In the last century observers such as Robert Jonckheere and Paul Muller were very active observers and discoverers. The latter also developed the doubleimage micrometer. The leading amateur was Paul Baize who was not only a prodigious observer but also computed orbits, many of which remain in the catalogue today. Antoine Labeyrie developed speckle interferome-try which has had a profound effect on the observation of very...

Bob Argyle

His blinkered interest in double stars dates back to the late 1960s and a period at the Royal Greenwich Observatory (RGO) at Herstmonceux in 1970 when he was let loose on the 28-inch refractor only made it worse. Occasional and all-too-short periods of observing occurred until 1990 when the RGO moved to Cambridge and Bob along with it. The availability of the 8-inch refractor satisfied a long-desired need for regular observation which is still in progress today. Bob works at the Institute of...

How to See the Diffraction Limit of any Telescope

Seeing is in some respect an art, which must be learnt The Airy diffraction pattern is not easy to observe astronomically in its full and perfect glory - practically, never in anything other than a small telescope (less than about 5 or 6 inches in aperture, the comments below referring primarily to larger instruments) under virtually perfect seeing conditions. Otherwise the best one can hope for is a partial, flickering view which it may take long experience as a telescope user to recognise as...

Making the Measurements

To aid further the determination of binary star astrom-etry, the Fourier transform can be used yet again. By calculating the transform of the power spectrum, these bands of light and dark can be converted into a sequence of three co-linear, circularly symmetric peaks. Binary star astronomers call this picture the autocorrelogram. The autocorrelogram consists of a large central peak and two smaller peaks, one on either side of the central peak, exactly 180 apart. Figure 17.3 shows a typical...

Reflectors versus Refractors Optical Principles

Even a cursory reading of the literature of visual double-star astronomy is sufficient to show that the field has long been heavily dominated by the refractor, which remains the instrument of choice for many visual observers. It is not, indeed, hard to find statements backed by the highest authority alleging that for this type of observation a reflector must be of substantially larger aperture to match the performance of a refractor of given size. For instance, van den Bos stated that a...

Photometry

One of the big advantages of the CCD camera is that it allows the measurement of a star's magnitude very accurately. Knowing the brightness (or magnitude) of a star is a fundamental property that is very important to astronomers and double star work. Precision of 0.01 magnitude can readily be obtained with a CCD camera. The simplest type of photometry1,4 is differential photometry. In differential photometry, a star with unknown magnitude is compared to a star with known magnitude, and from the...

The True Orbit

Double Stars Orbits

Whilst astronomers regard the brighter component as fixed and map the motion of the fainter one around it, in reality, both stars in a binary system move in ellipses around the common centre of gravity. The size of the ellipse is directly proportional to the mass of the star, so in the Sirius system, for instance, the primary has a mass of 1.5 M0, the white dwarf companion 1.0 M0 and so the size of ellipses traced out on the sky are in the ratio 1.0 to 1.5 for the primary and secondary (Figure...

Southern Hemisphere

In 1899 at the Royal Observatory at the Cape of Good Hope, R.T.A. Innes published A Reference Catalogue of Figure 24.1. Julie Nicholas, formerly Librarian at the Institute of Astronomy, with copies of Struves' first catalogue, the IDS (open on the desk), and the WDS (on CD-ROM). The latter could also contain every measure ever made. (R.Sword (IOA)) Southern Double Stars, but chose rather narrow limits to decide which pairs went in. In 1903 Innes became Government Astronomer at the Union...

The Apparent Orbit

Ascending Node

The apparent (observed) orbit results from a projection of the true orbit onto the celestial sphere (Figure 7.4). Three more elements determine this projection Q the position angle of the ascending node. This is the position angle of the line of intersection between the plane of projection and the true orbital plane. The angle is counted from north to the line of nodes. The ascending node is the node where the motion of the companion is directed away from the Sun. It differs from the second...

History of Double Star Observation

In 1610 the invention of the telescope by Galileo gradually led to the discovery of telescopic double stars but these were noted merely by the way. In 1617 Castelli found that Mizar was itself double4 and he later added a few more pairs. In 1664 Robert Hooke was observing the comet discovered by Hevelius when he came across Y Arietis, a pair of pure-white stars of 4th magnitude separated by some 8''. Over the next hundred years or so a few more double stars were noted but not catalogued in any...

The Thielevan den Bos Method

If the observational material does not allow the entire ellipse to be drawn, the Thiele-van den Bos method is recommended Figure 8.4 . It requires three well-observed places pi, di and the corresponding xi, yi and an approximate value for the areal constant c or alternatively the mean motion x. ellipse sector - triangle between three positions was found by Gauss. For a long time this method was used for the orbit computation of planets, but then Thiele2 applied the method to binary stars. Van...

Illuminated Reticle Eyepieces

Celestron Micro Guide Reticle

There are now readily available a number of proprietary eyepieces which are supplied by their manufacturers with illuminated reticle systems. They have completely transformed amateur double-star astrome-try.2 The Celestron Micro Guide eyepiece provides a typical example, but other makes are essentially similar this section refers specifically to the Celestron version . Reticle eyepieces of this type require the use of a motor-driven equatorial mount, with remote slow-motion controls to both...