LVAS OBSERVER’S CHALLENGE* – OCTOBER, 2018

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LVAS OBSERVER’S CHALLENGE* – OCTOBER, 2018 By Glenn Chaple for the LVAS
NGC 7129– Cluster/Nebula in Cepheus MAGNITUDE: 11.5 SIZE: 7’ X 7’

Young open star clusters are often embedded in the nebula that spawned them. An example is this month’s Observer’s Challenge, NGC 7129. This one-million-year-old cluster was discovered by William Herschel on October 18, 1794. Of NGC 7129 (H.IV-75 in his catalog), he wrote “Three stars about 9th magnitude involved in nebulosity.” It’s the nebulosity that must have impressed Herschel, as his Class IV was reserved for what he referred to as “Planetary nebulae.” The cluster itself is rather unimpressive, being comprised of a handful of 9th to 11th magnitude stars that form a group similar in appearance to the constellation Delphinus.

Once you’ve captured NGC 7129 in the eyepiece field, look one-half degree to the southeast for the 9th magnitude open cluster NGC 7142 (the unlabeled dotted circle in Chart B). NGC 7142 consists of several dozen magnitude 12-14 stars in an area about 10’ across. It was discovered by Herschel on the same night he found NGC 7129, and bears the Herschel identity H.VII-66 – his 66th Class VII (Pretty much compressed clusters) entry. NGC 7129 is about 3000 to 3300 light years away; NGC 7142 is some 2 times more distant. At an estimated age of 4 billion years, NGC 7142 is one of the oldest open clusters.

The charts below will help you locate NGC 7129, which is located about 4 ½ degrees NE of magnitude 2.5 Alderamin. Chart A shows the location of Alderamin in Cepheus. Chart B provides a star-hopper’s route from Alderamin to NGC 7129 and NGC 7142.

Chart A (www.constellation-guide.com)

Chart B (www.astrosurf.com)

Image of NGC 7129 and NGC 7142 (cs.astronomy.com)

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