Transit of Earth from Saturn
A '''[[astronomical transit|transit]] of [[Earth]] across the [[Sun]] as seen from [[Saturn (planet)|Saturn]]''' takes place when the planet Earth passes directly between the Sun and Saturn, obscuring a small part of the Sun's disc for an observer on Saturn. During a transit, Earth can be seen from Saturn as a small black disc moving across the face of the sun.
The event is particularly interesting because both the Earth and the [[Moon]] can usually be seen together in transit. In rare cases one of them transits and the other does not, because there is a grazing transit for one and a near-miss for the other. In other cases, the two May Be so close together that they are hard to tell apart, such as on [[July 21]] [[2020]], when the Earth and Moon are less than 5" apart at mid-transit.
Naturally, no one has ever seen a transit of Earth from Saturn, nor is this likely to happen in any foreseeable future. The last one took place on [[January 14]] [[2005]] -- though the [[Cassini]] probe was present in the Saturn system, it was also the day of the [[Huygens probe]] mission. Furthermore, the angular resolution needed to capture the occultation was near the limits of Cassini's imaging subsystem, to say nothing of the concerns of pointing the probe's camera directly at the Sun.
A transit could hypothetically be observed from the surface of one of Saturn's moons rather than from Saturn itself. The times and circumstances of the transits would naturally be slightly different.
The Earth-Saturn [[synodic period]] is 387.107 days. It can be calculated using the formula 1/(1/P-1/Q), where P is the [[sidereal year|sidereal orbital period]] of Earth (365.25636 days, not the same as a [[tropical year]]) and Q is the [[orbital period]] of Saturn (10746.940 days).
Note: the images linked to in the following table do NOT take into account the finite speed of light. The distance of Earth from Saturn at [[inferior conjunction]] is approximately 8.5 [[astronomical unit|AU]], which would correspond to about 70 light-minutes. It can take up to 11 hours for Earth to transit across the Sun at its widest point, thus the images correspond fairly closely to what would actually be seen by an observer on Saturn.
The images correspond to a hypothetical observer at the center of Saturn. Since Saturn has a large radius, the [[parallax]] of Earth between Saturn's center and its north or south pole would be about 9.7", which is about 4.5 times Earth's apparent angular diameter of 2.2", or about 4.5% of the Sun's angular diameter (about 3.5'). Therefore, some extremely close near-misses might be seen as grazing transits at Saturn's poles.
Near misses are indicated with <s>strikeout</s>.
{| border cellspacing=0 cellpadding=5 align="center"
!colspan="2"|Transits of Earth from Saturn
|-
| [[January 14]] [[2005]] || [http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=3&vbody=6&month=1&day=14¢ury=20&decade=0&year=5&hour=1&minute=0&fovmul=1&rfov=0.25&bfov=0.25&porbs=1]
|-
| <s>[[July 9]] [[2019]]</s>
|-
| [[July 21]] [[2020]]
|-
| <s>[[January 8]] [[2034]]</s>
|-
| <s>[[January 22]] [[2035]]</s>
|-
| [[July 15]] [[2049]]
|-
| [[January 16]] [[2064]]
|-
| [[July 11]] [[2078]]
|-
| <s>[[July 23]] [[2079]]
|-
| [[January 9]] [[2093]]
|}
==See also==
* [[Astronomical transit]]
{{transit visibility table}}
==References==
* C.T. Whitmell, ''Saturn visible through the Cassini Division'', Monthly Notices of the Royal Astronomical Society, '''62''' (1902), 457 [http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?journal=MNRAS&year=1902&volume=62&page_ind=455&letter=.&type=SCREEN_GIF]
==External links==
* [http://space.jpl.nasa.gov/ JPL Solar System Simulator]
[[Category:Astronomical transits]]
[[it:Transito della Terra da Saturno]]
[[zh:地球凌日 (土星)]]