Stellar Proper Motion,
24 February 2018 - 24 February 2019
Everything in the sky moves! Although stars are distant, they too move, some more than others, and their motions across the sky are called proper motions (PM). The star with the highest PM is Barnard's Star (HIP 87937 in Ophiuchus), moving at over 10 arcsec a year. Its PM can readily be detected in amateur telescopes and it is not unique in this.
In early 2018 I recorded the position of several stars with high PM, with a view to repeating the exercise at a later date. By good fortune, the weather was clear exactly one year later.
Below are comparison images, for four stars with high PM, taken on 04 February 2018 and exactly one year later. Now, for each star it is difficult to see the difference between the two images, so I created a third image by overlaying the two, inverting the top one and changing its transparency to 50%. If nothing changed in the year-long interval, the third image would be a uniform 50% grey. Any changes are immediately apparent, and an inset image shows the difference, created by the PM of the star, more clearly. The images of the high-PM stars are bloated by overexposure in order to capture fainter background stars. All images were taken with a Celestron EdgeHD 200 mm Schmidt-Cassegrain telescope with SBIG 8300 camera.
Luyten's Star (HIP36208) in Canis Minor. Magnitude 9.8 with a PM of 3.7 arcsec per year. In 2017 two planets were discovered in orbit.
Lalande 21185 (HIP54035) in Ursa Major. Magnitude 7.5 with a PM of 4.8 arcsec per year.
Gliese 412 (HIP54211) in Ursa Major. Magnitude 8.7 with a PM of 4.5 arcsec per year. It was not until I put this image together that I found that Gliese 412 is actually a double star with a magnitude 14.5 secondary.
Groombridge 1830 (HIP57939) in Ursa Major. Magnitude 6.4 with a PM of 7.1 arcsec per year. When discovered, this star had the highest PM of any known star, until superseded by Kapteyn's Star (in Pictor), then again by Barnard's Star. In this image, poor guiding has given the star a pear-shaped appearance: there is not a second unresolved companion!