Event Date: May 19th
Time: 10:00 PM
Brief
This evening, I will move from planets, asterisms, and everything else easily visible...except for Polaris! I have mentioned briefly in past entries that this star is easiest to see very close to the north celestial pole, hence its popular "north star" dubbing. While we often see this star with the eye all alone in a very small part of the sky as Ursa Minor [Little Bear's] tail, serious astronomers who do polar alignments with their telescopes get to know the surrounding star field. After so long, they (we) get to know it well enough over time, that they don't even need to refer to star fields in books, software or online. Here it is, within both a 2º field and a 1.4º one. The latter marked in light blue, marks precisely how far Polaris is from the north celestial pole" 41 arc-minutes.
Time: 10:00 PM
Brief
This evening, I will move from planets, asterisms, and everything else easily visible...except for Polaris! I have mentioned briefly in past entries that this star is easiest to see very close to the north celestial pole, hence its popular "north star" dubbing. While we often see this star with the eye all alone in a very small part of the sky as Ursa Minor [Little Bear's] tail, serious astronomers who do polar alignments with their telescopes get to know the surrounding star field. After so long, they (we) get to know it well enough over time, that they don't even need to refer to star fields in books, software or online. Here it is, within both a 2º field and a 1.4º one. The latter marked in light blue, marks precisely how far Polaris is from the north celestial pole" 41 arc-minutes.
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| click on image to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp. |
Detailed
Why have I labeled other stars in the image? They are all the next-"brightest" in apparent magnitude after Polaris, although hundreds of times dimmer! The brightest labeled is in the high-8th magnitude range, while the others are low to mid-9th magnitude. The 10th and 11th magnitude ones can still be seen in telescopes as small as 4", although a 6" or larger is recommended. The 8th and 9th are more helpful to center on the pole, being brighter.
Since Polaris spends the rest of the century, literally, approaching the north celestial pole as a result of axis precession its own proper motion, a slightly smaller field will eventually be needed to center telescopes at the axis. For now, the 2º is worthwhile using, marked in the different blue-shade. This way, other star patterns within the field may be helpful in aligning a telescope to the axis. The main reason for this alignment as a reminder--especially with equatorial telescopes--is improved tracking of the telescope in right ascension. However, alt/az telescopes lined up to the pole can also track better if motor-driven, as a special function on them is used to map out the sky.
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