A Visit to the Sky’s North Pole

Unlike the terrestrial North Pole, the heavenly version is easily accessible any clear night of the year. We explore curiosities within one degree of the celestial north pole and take a journey back in time. 

What could be more appropriate in January than a jaunt to the north celestial pole? When the polar vortex comes howling and temperatures plummet, consider a visit to the origin of all things north.

The center of the stellar merry-go-round

Because the planet's north polar axis points in the direction of Polaris, it remains nearly stationary in the sky as the stars wheel about it due to Earth's rotation.
Bob King

To keep things truly boreal, we're going to restrict ourselves to within one degree of the pole, or north of declination +89°. First and most obvious is the Pole Star itself — Polaris. The star's singular position at the sky's celestial pivot point has served to inflate its reputation into a common misconception. People think it's the brightest star in the sky! Yet the North Star's hardly in the running, ranking only 48th in brightness.

North Star with a bit of southwestern tang

Sketch of Polaris and its companion star 18″ to the southwest made using a 6-inch f/8 Newtonian reflector.
Jeremy Perez

Because Earth's axis points squarely at Polaris, as the planet rotates the star remains almost motionless in the heavens while all the others appear to turn about it. You can easily determine the height of Polaris above the local horizon by knowing your latitude. Live in Boston, Massachusetts, at 42° north? That's how high the North Star is above the northern horizon. Any stars within 42 degrees of Polaris never set and are said to be "circumpolar." Stars beyond that limit get cut off by the horizon for a period of time before rising into view again.

Through a 2.4-inch or larger telescope, Polaris is a pleasing double star with a considerably dimmer 9th-magnitude companion. When the brighter, showier Albireo (Beta Cygnii) is visible, I enjoy showing groups this star first and then surprising them with Polaris. Many will miss the fainter companion on a quick look but then have the pleasure of discovering it themselves with just a bit of effort.

Previous engagement at the north celestial pole

Polaris is the "diamond" in the Engagement Ring, a pretty asterism half a degree wide to its south.
David Ratledge

Things can be lonely at the pole, a relatively empty region of the sky, but Polaris glitters like a diamond atop a lovely asterism dubbed the "Engagment Ring," a loopy band of 9th-magnitude stellar gems plainly visible in telescopes and even in 50-mm binoculars under dark skies.

Closest to celestial north

Dim NGC 3172, the closest NGC object to the north celestial pole, and its fainter neighbor MCG +15-1-10 (right) to the west. Most sources list the brighter galaxy as ~1′ in diameter, but this image clearly shows a faint outer arm that expands its size to at least 3′.
David Ratledge

Moving deeper, we encounter a pair of deep sky objects located just 55′ from the polar pivot, the spiral galaxy NGC 3172 and MCG +15-1-10. Also called Polarissima Borealis because of its proximity to the north celestial pole, NGC 3712 glows feebly at magnitude 13.6 and will prove a challenge for a 10-inch telescope under dark skies. In my 15-inch Obsession it's a dim, round patch with a brighter center. For those who like their fuzzies faint, try spotting its 15th-magnitude neighbor about 2′ to the west.

One of the bonuses of observing objects near the celestial pole is not having to worry about tracking your target. An object centered in the field of view will stay there for many minutes without the need to nudge the telescope — a real pleasure for those with non-motorized Dobsonian reflecting telescopes.

Polaris not a perfect pole star

Annotated photo showing Polaris, the Ring, the closest relatively bright star to the north celestial pole (NCP) and the NCP. In this 200mm telephoto view, it's easy to see that Polaris isn't quite centered on the NCP. Click image for a map to help you also find Polarissima Borealis.
Bob King

The closest "bright" star to the north celestial pole is 9.7 magnitude SAO 3788, presently about 15′ (1/4°) away. Due to the precession of Earth's axis, Polaris has only been close enough to assume the role of pole star since the early medieval days. Around the time of Caesar, both it and Kochab, an equally bright star in the Little Dipper's bucket, were nearly equidistant from the pole.

Big belly leads to ever-changing pole stars

Precession is a cyclic wobble of the Earth's axis with a period of about 26,000 years caused by the Sun and Moon's gravity acting on the planet's equatorial bulge. The polar axes describe a circle in the sky during each cycle. Where they point along that circle determines the pole stars of that epoch.
NASA (left); Wikipedia - Tau'olunga

Polaris has been inching poleward for centuries and will reach a minimum distance of 27′ — just under 1/2° or one Full Moon diameter — in March 2100. The news will undoubtedly be a hot topic on what remains of the Internet in that distant year. Will someone scheme up a doomsday scenario where the pole star focuses magnetic beams on a hapless humanity? Don't doubt it.

No place to hang your hat in Caesar's day

During Caesar's reign, no pole star lay near the north celestial pole (NCP). Both Polaris and Kochab (Beta UMi) were approximately equidistant from it. 2000 years of precession has since guided Polaris to the coveted spot. This map shows the sky around 8 o'clock January 7, 45 BC over Rome.
Source: Stellarium, Wikipedia

Long before the reign of Polaris, when the Great Pyramid was built in Giza around 2550 BC, 3.6-magnitude Thuban (Alpha Draconis) marked the polar point. At magnitude 2.0, Polaris has been the brightest pole star since 12,000 BC when Vega last had a run at it. Once Polaris begins its slow departure in 2100, it won't return again to polar glory until AD 28,000!


Can't find the pole star? Let a Sky & Telescope Star Wheel guide you!

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Astronomy Blogs, Explore the Night with Bob King, Observing
Bob King

About Bob King

Amateur astronomer since childhood and long-time member of the American Association of Variable Star Observers (AAVSO), Bob King also teaches community education astronomy and writes the blog Astro Bob. The universe invites us on an adventure every single night. All we need do is look up. Check out my forthcoming book "Night Sky with the Naked Eye" (on Amazon and BN) about all the great things you can see at night without any special equipment.

2 thoughts on “A Visit to the Sky’s North Pole

  1. Marc

    Hi Bob,

    Great article, especially for a novice like me.

    I have a question: why is it that the Earth spins one way but the precession of the NCP is in the opposite direction? If you spin a toy top (the usual analogy) the direction of axial precession and the top’s spin direction are the same.

    Kind regards
    Marc Inzani
    London, UK

    1. Bob KingBob King Post author

      Marc,
      Great question! I wish I could give you a definitive answer. A top will precess in a direction determined by the torque exerted by its weight. Earth precesses due to the gravity exerted by Sun and Moon on its equatorial bulge. I can only guess that different kinds of torques produce the difference in precession.

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