Observing Titan's shadow; will an 8 inch show the shadow?

[spaceboy0]

When Saturn's rings are exactly edge on, would that indicate the planet's declination is exactly zero degrees?

I guess I'm trying to understand the connection between Saturn's declination and the orientation of the rings.

[RickJ]

Darn, I posted my reply and only part of the first sentence was posted and I didn't save it. Trying again.

No. Note we have two or 4 crossings at a ring crossing event. These can cover many months. There will always be one ring crossing as seen from the sun and one as seen from the earth. There can be three as seen from earth as in the 1979-80 crossing. The sun crossing event happens at the exact time of Saturn's equinox when the rings are hidden by their own shadow. The 79-80 crossing is a good example.

The first crossing as seen from earth happened on October 27th, 1979 at a declination of about +4.5 degrees.

The sun crossing happened on March 3, 1980 at +4.25 degrees.

The next earth crossing was March 12 at +4.6 degrees

The final earth crossing was July 23 at +4.5 degrees

This year the sun crossing is August 10th at +5.67 degrees with the earth crossing September 4th at +4.5 degrees.

Other crossings happen with Saturn south of the celestial equator. Any good planetarium program should help you explore this.

Rick

[spaceboy0]

what are the ring crossing dates this time?

[Kyle Edwards]

When Saturn's rings are exactly edge on, would that indicate the planet's declination is exactly zero degrees?

I guess I'm trying to understand the connection between Saturn's declination and the orientation of the rings.

No, Declination in the equatorial system is based off the axis of Earth's rotation.

When the rings are edge on, it would mean that the declinaion of Earth with respect to the north pole of the plane of the Saturn's rings is exactly 0.

And since the rings are very close to Saturn's equatorial plane, it would mean that the declination of Earth as seen from Saturn would be very close to zero.

[spaceboy0]

Am I correct in assuming that if Saturn's orbital inclination around the Sun was zero degrees relative to Earth, then at ring crossing Saturn's declination would be zero degrees?

[Kyle Edwards]

Am I correct in assuming that if Saturn's orbital inclination around the Sun was zero degrees relative to Earth, then at ring crossing Saturn's declination would be zero degrees?

I don't think so. It would all depend on the north pole of saturn's ring plane. In the case you described, saturn's ecliptic latitude would always be zero though.

Since the rings pretty much line up with Saturn's equatorial plane, if you were "standing" on Saturn during a time where the rings were edge on from Earth, the Earth would appear at 0 declination relative to Saturn's north celestial pole. And since the Earth would never appear more than a few degrees from the Sun, this would be around the time of an equinox.

The point in the sky as seen from Earth that is Saturn's north celestial pole is 40.589 degrees RA and 83.537 degrees DEC according to the IAU. So while the difference in inclination does have some effect on how we see Saturn's rings (and in what position Earth appears from Saturn), the different equatorial planes have a much greater difference.

The same calculations that can be used to dermine which angle we will see Saturn's rings can also be used to find out which latitudes of Mars or any other planet will be visible. Basically that is just finding out the RA and DEC of where the Earth will appear from that planet based on that planet's equatorial plane.

http://astrogeology.usgs.gov/Projects/WGCCRE/constants/iau2000_table1.html

Hope this helps.

[spaceboy0]

If Saturn's NCP is at Dec 83.537 degrees, then would that imply that Saturn's equator is tipped the difference between 90 and 83.537 or 6.46 degrees to it's orbit plane?

[Kyle Edwards]

If Saturn's NCP is at Dec 83.537 degrees, then would that imply that Saturn's equator is tipped the difference between 90 and 83.537 or 6.46 degrees to it's orbit plane?

According to wikipedia Saturn is tipped 26.73 degrees from it's orbital plane.

The RA and DEC values for it's north celestial pole are just referencing the point in the in the Earth's equatorial system that Saturn's rotational axis is pointed at. So if I am not mistaken, Saturn's equatorial plane would be tipped around 6.46 degrees from Earth's equatorial plane.

Hope this helps. I am writing a solar system simulator program and the diffrent refernece planes used can get confusing.

Here is an article you might find helpful. http://en.wikipedia.org/wiki/Axial_tilt
And if you are interested in learning some of the calculations this is a great book. Meeus devotes an entire chapter to Saturn's rings. http://www.amazon.com/Astronomical-Algorithms-Jean-Meeus/dp/0943396611/ref=sr_1_2?ie=UTF8&s=books&qid=1239836758&sr=8-2

Kyle Edwards

[spaceboy0]

So the Ascending Node and Descending Node would be the points where Earth's and Saturn's orbits intersect (two points)

[Tucson_Tim]

Your older thread has some good info:

http://www.bautforum.com/astronomical-observing-equipment-accessories/71066-has-anyone-seen-titans-shadow-saturn.html