Star Hopping Between Gamma Cassiopeiae and Gamma Cephei Locates NGC 40

Summary: Star hopping between Gamma Cassiopeiae and Gamma Cephei locates NGC 40, the planetary nebula in constellation Cepheus discovered by William Herschel.

Star hopping between Gamma Cassiopeiae (marked, center left, as γ Tsih, its Chinese name, meaning “whip”) and Gamma Cephei (marked, top center, as γ Errai, its IAU-approved proper name, derived from Arabic for “shepherd”) locates NGC 40 (upper center); aim point Uranus discoverer Sir William Herschel discovered NGC 40 (off-center left), a planetary nebula in Cepheus the King constellation, Nov. 25, 1788; aim point RA: 0h 13m Dec: +72°32' Tue 1788 Nov 25 4:14 UTC: John Walker/Your Sky, Public Domain, via Fourmilab Switzerland

Star hopping between Gamma Cassiopeiae and Gamma Cephei locates NGC 40, the planetary nebula in Cepheus the King constellation discovered Nov. 25, 1788, by Uranus discoverer Sir William Herschel.

The Bow Tie Nebula NGC 40 claims Cepheus as parent constellation. Cepheus the King constellation’s placement in the upper reaches of the Northern Celestial Hemisphere qualifies the kingly constellation for status as one of the terrestrial Northern Hemisphere’s five main circumpolar constellations. Location in proximity to the celestial north pole characterizes the Northern Hemisphere’s circumpolar constellations. Cepheus’ circumpolar neighbors comprise Ursa Minor the Lesser Bear, Camelopardalis the Giraffe, Draco the Dragon and Cassiopeia the Seated Queen.

Cassiopeia the Seated Queen and Cepheus the King neighbor each other as wife and husband in the celestial representation of the Greek myth involving their daughter, Andromeda. Constellation Andromeda the Chained Princess lies south of constellation Cassiopeia.

Cepheus lies to the north and west of Cassiopeia. Star hopping via the neighboring constellations’ third brightest stars easily locates NGC 40. Second magnitude binary star Gamma Cassiopeiae (γ Cassiopeiae; Gamma Cas, γ Cas) shines as Cassiopeia the Seated Queen constellation’s third brightest star. Third magnitude binary star Gamma Cephei (γ Cephei; Gamma Cep, γ Cep) rates as Cepheus the King constellation’s third brightest star. Both star systems claim conspicuous positions in their respective constellations.

Gamma Cassiopeiae occupies the center of constellation Cassiopeia’s distinctive W-shaped asterism, or recognizable pattern of stars. Gamma Cassiopeiae perches at the peak that joins the letter’s two component vees.

The traditional outline of constellation Cepheus resembles a child’s stick drawing of a house, composed of a square topped by a triangle. Gamma Cephei marks the tip of the roof.

An imaginary line drawn between the two Gammas passes through NGC 40. Starting the line at Gamma Cephei places NGC 40 at about one-third of the star-hopping distance.

The planetary nebula, which hovers toward Cepheus’ northeastern border, lies closer to Gamma Cepheus than to Gamma Cassiopeiae. Beginning with Gamma Cassiopeiae increases the travel along the imaginary line to two-thirds of the star-hopping distance.

The selection of Gamma Cassiopeiae or Gamma Cephei as the starting point depends upon convenience, familiarity and preference. Cassiopeia’s W-shaped asterism claims attention as a bright, distinctive pattern of stars. Cepheus’ house-shaped asterism also makes a prominent appearance in the night sky.

The naked-eye guides of Gamma Cassiopeiae and Gamma Cephei help observers to pinpoint the area of the sky at which to aim their telescopes. Amateur astronomer and retired middle school science teacher Glenn Chaple suggests centering the finderscope on the targeted area and conducting a low-power search, with a 50X telescope, for an “out-of-focus 12th magnitude star midway between and slightly west of a pair of 9th magnitude stars.” A dark sky brings NGC 40 into view via a 4-inch scope. Chaple notes that significant details emerge with twice that aperture. He recommends magnifications beginning at 150X for observations of the nebula’s 11.6 magnitude central star in its setting of “a slightly oval 35 X 38 arc second haze.”

Chaple shares a fun aspect of observing NGC 40. The nebulosity seems to vanish when focusing attention on the planetary nebula’s central star. Averting the gaze away from a direct view of the central star restores awareness of the nebulosity. Chaple equates the nebulosity’s vanishing and reappearance to the blinking in and out of view effect exhibited by NGC 6826.

Known as the “blinking planetary,” NGC 6826 also numbers among Sir William Herschel’s discoveries. Sir William discovered the planetary nebula in Cygnus the Swan constellation Sept. 6, 1793.

The takeaway for star hopping between Gamma Cassiopeiae and Gamma Cephei to locate NGC 40 is that the third brightest stars in neighboring constellations Cassiopeia the Seated Queen and Cepheus the King strategically frame an imaginary line that passes through the Cepheid planetary nebula discovered Nov. 25, 1788, by Uranus discoverer Sir William Herschel.

Hubble Space Telescope color image of NGC 40 (lower left), with the planetary nebula's central star; RA 00:13:00.65, DEC 72:31:22.2; Nov. 10, 1995; image NGC40 (color) PC f814w/f555w PC1 06119_01: HLA (Hubble Legacy Archive), via HLA-STScI (Space Telescope Science Institute)

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Star hopping between Gamma Cassiopeiae (marked, center left, as γ Tsih, its Chinese name, meaning “whip”) and Gamma Cephei (marked, top center, as γ Errai, its IAU-approved proper name, derived from Arabic for “shepherd”) locates NGC 40 (upper center); aim point Uranus discoverer Sir William Herschel discovered NGC 40 (off-center left), a planetary nebula in Cepheus the King constellation, Nov. 25, 1788; aim point RA: 0h 13m Dec: +72°32' Tue 1788 Nov 25 4:14 UTC: John Walker/Your Sky, Public Domain, via Fourmilab Switzerland @ http://www.fourmilab.ch/cgi-bin/Yourtel

Hubble Space Telescope color image of NGC 40 (lower left), with the planetary nebula's central star; RA 00:13:00.65, DEC 72:31:22.2; Nov. 10, 1995; image NGC40 (color) PC f814w/f555w PC1 06119_01: HLA (Hubble Legacy Archive), via HLA-STScI (Space Telescope Science Institute) @ http://hla.stsci.edu/hlaview.html#Inventory|filterText%3D%24filterTypes%3D|query_string=ngc%2040

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