Inspired by Marc’s heroic 2650 mm focal length images of M8 and M20, I decided to try a little long FL imaging myself, but at a much more modest 1932mm. With Neptune making an evening appearance, I thought that Nereid, discovered in 1949, would make a good target. I recently purchased a copy of SkyTools 4 Imaging, as with this major release, the author has added several new and interesting objects such as Nereid.
Nereid is the third largest of Neptune’s moons, and the second to have been discovered. It was discovered on 1st May, 1949 by the Dutch American astronomer Gerard P. Kuiper (for whom the Kuiper Belt is named) using photographic plates from the McDonald Observatory in Fort Davis, Texas. It is named after the numerous daughters, called Nereids, of the sea god Nereus in Greek mythology.
Almost everything we know about Nereid comes from the images taken by Voyager 2 in 1989; its closest approach was approximately 4.7 million km.
Nereid has a diameter of about 340 km (210 miles). It revolves around Neptune with a period of just over 360 days in a highly elliptical orbit—the most eccentric of any known moon—that is inclined by more than 7° to the planet’s equator. Its mean distance from Neptune is 5,513,400 km (3,425,900 miles), which is about 15 times farther from Neptune than Triton. Nereid is exceedingly faint, making observations with even the largest Earth-based telescopes very difficult.
Nereid’s highly eccentric orbit (eccentricity 0.75, the highest of any solar system moon) takes it from 1.37 million km from Neptune to 9.66 million km (average 5.51 million km); unlike Triton, and like the other inner moons, Nereid’s orbit is prograde. This suggests that it may be a captured Kuiper Belt object, or that its orbit was substantially perturbed when Triton was captured.
The attached images were taken using a Tak Mewlon 210, Tak x0.8 Reducer/Flattener and an SBIG ST2000XM camera. I captured 30x300 sec frames on 1st Sept 2019. I had to discard some of the early frames where Nereid was at less than 45 degrees altitude, due to the smearing effects of the atmosphere. The faint dot of Nereid tightened and became more obvious as the object approached the meridian. Images were calibrated, aligned and stacked using CCDStack2 and finished in PS CS. I blended in a single 300 sec regions showing Neptune and Triton as the movement over the frames blew this region out.
I have overlayed skycharts from SkyTools 4 and The Sky X Pro to identify some of the other objects in the field. I have also included a DSS image (colour) from Astrometry.Net showing the field - wish I had their telescopes...
In 2001, two surveys using large ground-based telescopes – the Cerro Tololo Inter-American Observatory and the Canada-France-Hawaii telescopes – found five additional outer moons bringing the total to thirteen. Follow-up surveys by two teams in 2002 and 2003 respectively re-observed all five of these moons – which were Halimede, Sao, Psamathe, Laomedeia, and Neso.
And then on July 15th, 2013, a team of astronomers led by Mark R. Showalter of the SETI Institute revealed that they had discovered a previously unknown fourteenth moon in images taken by the Hubble Space Telescope from 2004–2009. The as yet unnamed fourteenth moon, currently identified as S/2004 N 1, is thought to measure no more than 16–20 km in diameter.
Image centre: RA 23h 15m 06.957s: DEC -05° 57' 39.306"
FOV: 12.7 x 9.55 arcmin
Image Scale: 0.746 arcsec/pixel
Nereid
Magnitude: 18.69
PA: 62.7 deg
Separation: 455.1”
Earth Distance: 28.9 AU
Cheers
Dennis