Here is my second attempt at recording Nereid, the outermost known moon of Neptune from its discovery in 1949 (by G. Kuiper) until 2002. The mean radius of Nereid is 170km and it has a magnitude of 18.72. The orbital period of Nereid is listed as 360.13619 days and its highly eccentric orbit helped keep the much brighter Neptune (7.83m) outside the field of view.
Using the NASA (JPL) Horizons system, I generated an ephemeris for the 15th August 2009 at 1 hour intervals and then slewed the ‘scope to the coordinates generated by Horizons.
The parent planet Neptune (diameter 49,528.0 km) lies some 2.796 billion miles from the Sun and has a rather chilly surface temperature of -209°C.
The attached image shows Nereid in the bottom left hand corner with an inverted inset to better show the motion trail over the 7 x 20 minute exposures. I have also included an inverted image and animation revealing Nereid’s movement over some 140 minutes.
Thanks Andrew, Ric, Al & Trevor, for those nice words – I appreciate your comments!
Ric: Starry Night Pro Plus 6 showed the separation of Neptune and Nereid to be 5min 42sec, or 342 arcsec. This is a very useful gap as the long exposures required for Nereid (18.72m) would cause severe blooming of Neptune (7.83m) with my non anti-blooming ccd camera.
Trevor: Yes a great project indeed. Also, from a darker site, the flux of Nereid above background would be better than my Brisbane skies!
Those are awesome pictures, congratulations! It's great to see such an unusual target being imaged.
Do you know how much of the movement is due to Nereid orbiting Neptune compared to the Neptunian system orbiting the Sun?
Those are awesome pictures, congratulations! It's great to see such an unusual target being imaged.
Do you know how much of the movement is due to Nereid orbiting Neptune compared to the Neptunian system orbiting the Sun?
Hi Rolf
Thank you! I think that there are 3 main components of the apparent movement of Nereid in this 140 minute sequence;
Orbit of the Earth around the Sun (12 months)
Orbit of Nereid around Neptune (360 days)
Orbit of Neptune around the Sun (164 years)
I think that the distance travelled by the Earth along its orbit in the 140 minutes is by far the most predominant as Neptune moves quite slowly, taking almost 164 years to complete an orbit, compared to 12 months for our home planet.
See this post where Rob_K (msg#7) did a quick calculation on a previous post showing a Pluto animation.
The recent spell of consecutive clear nights in Brisbane has been a blessing, as I have now managed to fine tune my mount and software to allow for extended exposures at these longer focal lengths, something I had been struggling with previously.
Thank you! I think that there are 3 main components of the apparent movement of Nereid in this 140 minute sequence;
Orbit of the Earth around the Sun (12 months)
Orbit of Nereid around Neptune (360 days)
Orbit of Neptune around the Sun (164 years)
I think that the distance travelled by the Earth along its orbit in the 140 minutes is by far the most predominant as Neptune moves quite slowly, taking almost 164 years to complete an orbit, compared to 12 months for our home planet.
See this post where Rob_K (msg#7) did a quick calculation on a previous post showing a Pluto animation.
Cheers
Dennis
That's amazing. I hadn't throught of the parallax effect but yes it must be the biggest contributor. Thanks for the info!
Jeff – I have found that with my set up, skies and techniques, Nereid is so much easier than Sycorax, although I do occasionally get the itch to have another go at that Uranian moon but if I do, it will be a dark sky site to allow me to take longer subs.
