Saturn ring-plane crossing

Jump to August 1995 images

Every 13-15 years, the Sun and Earth cross the plane of Saturn's rings. On these occasions, the rings are seen exactly edge-on. This relatively rare event will occur during 1995-1996. Because the Earth's orbit, Saturn's orbit, and the ring-plane are not exactly coplanar, a series of events will occur:

May 22, 1995, 05:18 UT - Passage of the Earth through ring-plane of Saturn from North to South (Saturn will only be accessible in the east for a few hours before sunrise)
Aug 10, 1995, 20:54 UT - Passage of the Earth through ring-plane of Saturn from South to North (Saturn will be well placed in the night sky for detailed observations)
Nov 19, 1995, 15:09 UT - Passage of the Sun through ring-plane of Saturn
Feb 11, 1996, 23:34 UT - Passage of the Earth through ring-plane of Saturn from North to South

The University of Hawaii 2.2-meter telescope will be used to study these events. For the May 1995 event, a large format (1024x1024) near-infrared camera will be used to search for new small satellites, and to characterize the G- and E-rings. In August 1995, a coronagraph with CCD camera will be used. Astronomers at the University of Hawaii will also be using other telescopes on Mauna Kea to study the ring-plane crossings. As observations of the ring-plane crossing become available, images will be posted here. Images currently available are:

May 1995

May 14 (UT) 2.1 micron image (90k) - obtained by Kevin Jim and Andrew Pickles; image processing was performed by Richard Wainscoat. This image was made using the University of Hawaii's 2.2-meter telescope with its tip-tilt secondary mirror in operation (guiding on the satellite Tethys). The tip-tilt guiding removed some of the atmospheric distortion, and also removed buffeting of the telescope by a moderate wind from the east. Exposure time was 8 seconds through the K' filter. Saturn is relatively dark around 2 microns due to methane absorption in its atmosphere. This image has a resolution of 0.50 arcsec, and was taken at an airmass of approximately 1.9. Two satellites may be seen to the left of the rings - these are Tethys (brighter) and Enceladus (fainter). The shadow of the rings produces the dark line across Saturn's equator. A false color (112k) version of this image is also available. Note the shadow of Saturn on the rings near Saturn's western (right) limb.
A deconvolved version of the May 14 image (44k) is now available, and is also available in false color (62k). Since no true point source was available, Tethys was used as the point source for this deconvolution. Tethys is not quite a point source (diameter 0.145 arcsec), so some low level artifacts result from the deconvolution.
May 20 (UT) K-band image (2.2 micron) (17k). This is a 1-second sky-subtracted exposure, displayed with a logarithmic stretch. North is at the top, and east is at the left. To the east, Rhea and Tethys (farthest east) may be seen. West of Saturn is Enceladus. This image was obtained by Christophe Dumas, Natalie Domergue-Schmidt, Joe Jensen, and John Dvorak with the University of Hawaii 2.2-meter telescope.
May 21 (UT) J-band image (1.2 microns) (7k) which shows the very faint E-ring. The integration time was 11 minutes and the image was taken at approximately 14:45 UT (about 50 minutes before sunrise). The bright spot on the left is Rhea, and is saturated in this deep exposure. The scattered light comes from the A ring and Saturn. This image was taken through thin cirrus. The observers were Christophe Dumas, Natalie Domergue-Schmidt and John Dvorak with the University of Hawaii 2.2-meter telescope.
May 22 (UT) K-band image (2.2 microns) (19k) constructed from six 60 second exposures. The dark side of the A-ring is visible; the satellites are slightly elongated because of their orbital motion during the exposure. The contrast has been modified to try to show very faint satellites such as Helene (about K=17.5), and Janus (about K=14), located inside the A ring. The observers were Christophe Dumas, Natalie Domergue-Schmidt, and John Dvorak; the image was obtained with the University of Hawaii 2.2-meter telescope.

August 1995

Aug 09 (UT) R-band coronagraphic image (37k) which shows the faint E-ring. This is a short, 60 second exposure. The occulting disk in the coronagraph has a diameter of 30 arcseconds, and the image area shown measures approximately 160 x 160 arcseconds. The bright A-ring can be seen near the edge of the occulting disk. The bright satellites to the east (left) of Saturn are Tethys and Dione. A deeper display (74k) of the same image shows that E-ring stretching almost to the edge of the image. The E-ring can be seen extending out to about 7 Saturn radii. A 20 second R-band exposure (83k), taken 90 minutes later, may also be viewed. This image has been processed to remove circularly symmetric scattered light around the occulting disk - it shows the inner A-ring more clearly, and also shows the E-ring extending outward to about 65 arcseconds from the center of Saturn. A faint satellite is visible between Tethys and Dione.
The observers were David Jewitt and Paul Kalas; the images were obtained with the University of Hawaii 2.2-meter telescope. Only minimal processing has been applied to these data.
Aug 10 (UT) R-band coronagraphic image (54k) which shows the faint E-ring. This is a short, 60 second exposure through a red filter. The satellites to the east (left) of Saturn are Rhea (saturated) and Dione (saturated, on ring). To the west of Saturn are Mimas (on the right hand edge of the A-ring), and Tethys (also saturated). Between Mimas and Tethys are the much fainter satellites Helene and Telesto (fainter). A deeper display (78k) of the same image shows the E-ring extending out beyond Tethys. This image can also be viewed with circularly symmetric scattered light subtracted.
A short 10 second R-band exposure (52k), taken 36 minutes later may also be viewed - this image shows more detail of the inner A-ring. A deeper display (82k) is also available, as is a version with circularly symmetric scattered light subtracted.
The observer was David Jewitt; the images were obtained with the University of Hawaii 2.2-meter telescope. Only minimal processing has been applied to these data.
Aug 11 (UT) R-band coronagraphic image (54k). The ring plane crossing occurred about 15 hours before this 60 second exposure was taken. The A-ring has become remarkably brighter. This is because for the time between the first ring plane crossing on May 22 UT, and the second ring plane crossing (Aug 10 UT), we were viewing the dark side of the rings, but now we are seeing the side which is illuminated by the Sun. The A-ring is thoroughly saturated in this image. A direct comparison between Aug 10 UT and Aug 11 UT images (68k), each with the same exposure time, clearly shows how bright the inner rings have become. The faint E-ring is still visible in a deeper display (70k) of the same image. This image can also be viewed with circularly symmetric scattered light subtracted (126k). The bright satellites are, left to right, Tethys, Enceladus and Rhea, to the east of Saturn, and Dione to the west of Saturn.
The A-ring has now become so bright that only very short exposures with a CCD on a large telescope remain unsaturated. A 5 second R-band exposure (47k), taken about one hour earlier, was the longest exposure which didn't saturate the inner ring. Note that the very bright disk of Saturn, and most of the ring system which we usually see (A, B, C rings), are hidden behind the occulting spot of the coronagraph. The very faint E-ring can still be seen in a deeper display (149k) of the same image.
The observer was David Jewitt; the images were obtained with the University of Hawaii 2.2-meter telescope. Only minimal processing has been applied to these data.

Additional sources of information:

Saturn Ring Plane Crossings of 1995-1996 (JPL)

IfA Home Page

Last updated August 10, 1995

Richard Wainscoat
rjw@ifa.hawaii.edu