This month we travel from the North Celestial Pole to the North Ecliptic Pole
1. Polaris ‘Engagement Ring’
Recommended equipment: 10×50
Most astronomers use mag. +2.0 Polaris (Alpha (α) Ursae Minoris) as a mere marker for the North Celestial Pole (NCP), but binoculars reveal that it is part of an asterism, a circlet of mostly 8th and 9th magnitude stars: like a diamond in an engagement ring. Notice that one of the stars in the circlet is slightly displaced away from Polaris; this star is on the line joining Polaris and the NCP, and enables the NCP to be more precisely located.
2. Galaxy pair M81 and M82
Recommended equipment: 15×70
The next stop in this month’s tour of the north polar region of the sky takes us to the galaxy pair M81 (Bode’s Galaxy) and M82 (The Cigar Galaxy). Use the chart to help you identify mag. +4.6 24 Ursae Majoris and you should be able to get the galaxies in the same field of view. M81 is the brighter and easier of the pair; fainter M82 may need averted vision.
3. Kappa Dra group
Recommended equipment: 10×50
Our next target is an attractive little line of coloured stars. The brightest of these is the hot (13,727˚C) blue-white mag. +3.9 Kappa (κ) Draconis, which shines brighter than 500 Suns. To the north are two orange stars, the brighter of which is mag. +4.9 6 Draconis. At the other end of this line of four, the most southerly star is ruddy 4 Draconis, a long-period pulsating variable (mag. +4.9 to +5.0).
4. ΟΣΣ123
Recommended equipment: 10×50
ΟΣΣ123 is at the end of a 4°-long chain of stars that extends west from mag. +3.7 Thuban (Alpha (α) Draconis). With magnitudes of +6.6 and +7.0, and a separation of 69 arcseconds, the components of this double star are easy to split. The ‘ΟΣΣ’ designates Otto Wilhelm von Struve’s catalogue of double stars. Otto Wilhelm was one of 18 children of the 19th-century astronomer Friedrich Georg Wilhelm von Struve.
5. Kemble 2
Recommended equipment: 10×50
In the same field of view as mag. +3.6 Chi (χ) Draconis, only 1° to the east, is a little equilateral triangle of 7th magnitude stars. You will see a pair of fainter stars that complete a trapezium, of which the triangle is a part; it forms a ‘W’ with the fainter stars at the tips. This similarity to the ‘W’ of Cassiopeia gives the group its name, ‘Little Queen’.
6. Cat’s Eye Nebula
Recommended equipment: 15×70
We end with the Cat’s Eye Nebula, which marks the position of the North Ecliptic Pole, a point on the northern celestial hemisphere that is always the same angular distance from the Sun, which is the centre of the circle that the NCP makes in its 25,770-year precessionary cycle. It looks like an ethereal green star and winks at you if you change from averted to direct vision.