APOD: The Moon Eclipses Saturn (2014 Jul 16)

[APOD Robot]

The Moon Eclipses Saturn

Explanation: What happened to half of Saturn? Nothing other than Earth's Moon getting in the way. As pictured above on the far right, Saturn is partly eclipsed by a dark edge of a Moon itself only partly illuminated by the Sun. This year the orbits of the Moon and Saturn have led to an unusually high number of alignments of the ringed giant behind Earth's largest satellite. Technically termed an occultation, the above image captured one such photogenic juxtaposition from Buenos Aires, Argentina that occurred early last week. Visible to the unaided eye but best viewed with binoculars, there are still four more eclipses of Saturn by our Moon left in 2014. The next one will be on August 4 and visible from Australia, while the one after will occur on August 31 and be visible from western Africa at night but simultaneously from much of eastern North America during the day.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[inertnet]

How is this possible? Our moon is a lot smaller than both Saturn and the sun, so it shouldn't be able to cast such a giant shadow on Saturn.

EDIT:
Aha, I see, the moon blocks part of Saturn. The title "The Moon Eclipses Saturn" made me assume a shadow was cast.

Next time I'll put on my reading glasses and read the description first

[Nitpicker]

The Moon is not casting a shadow on Saturn. The Moon is simply beginning to pass in front of Saturn, from the photographer's point of view. The leading (western) limb of the Moon is in shadow and it is this limb that we see blocking one half of Saturn.

[Boomer12k]

Cool....haven't seen a close up of The Moon in awhile....and Saturn too....GREAT!

:---[===] *

[Deric]

I enjoy your daily photos very much, and I like to think I learn something from you every day -- but today's effort was disappointing. Why use 'eclipse' (which is not happening) when you really mean 'occult'? You guys know the difference, but many of us don't. Teaching your readers the proper terms is a good goal, but giving them the wrong one in the headline (even if you correct it in the text) is a mistake. The first commenter was evidently confused.

Accuracy, please. Otherwise, you are contributing to the dumbing down of society.

[neufer]

I enjoy your daily photos very much, and I like to think I learn something from you every day -- but today's effort was disappointing. Why use 'eclipse' (which is not happening) when you really mean 'occult'? You guys know the difference, but many of us don't. Teaching your readers the proper terms is a good goal, but giving them the wrong one in the headline (even if you correct it in the text) is a mistake. The first commenter was evidently confused.

Accuracy, please. Otherwise, you are contributing to the dumbing down of society.

OCCULT, a. [L. occultus, occulo; ob and celo, to conceal.] (Webster 1828)

• Hidden from the eye or understanding; invisible; secret; unknown; undiscovered; undetected; as the occult qualities of matter.
  
  The occult sciences are magic, necromancy, &c.
  
  Occult lines, in geometry, are such as are drawn with the compasses or a pencil, and are scarcely visible.

--------------------------------------------------------------------------------
ECLIPSE, n. [L. eclipsis; Gr. defect, to fail, to leave.] (Webster 1828)

• 1. Literally, a defect or failure;
  hence in astronomy, an interception or obscuration of the light of the sun, moon or other luminous body.
  
  2. Darkness; obscuration. We say, his glory has suffered an eclipse.

<<An occultation occurs when an apparently larger body passes the next planet in front of an apparently smaller one. A transit occurs when a smaller body passes in front of a larger one. In the combined case where the smaller body regularly transits the larger object, an occultation is also termed a secondary eclipse.

An eclipse occurs when a body disappears or partially disappears from view, either by an occultation, as with a solar eclipse, or by passing into the shadow of another body, as with a lunar eclipse.>>

[mwhidden]

Would I be able to view the August 31st daytime occultation of Saturn from New England with a cheap ~2" refractor?

I'm having a hard time understanding the chart at http://asa.usno.navy.mil/cgi-bin/occnwd ... ody=Saturn. Does it mean the the occultation begins in southern New England about 60 minutes (6 of the 10 minute rings from the western red ring) after first shadow at 14:48UT1, or is it 60 minutes before last shadow at 17:17?

Also, what does the Delta T=TT-UT1 = 67s mean?

[Chris Peterson]

Would I be able to view the August 31st daytime occultation of Saturn from New England with a cheap ~2" refractor?

Easily. A pair of binoculars will do, also.

[JuanAustin]

for some reason i never thought saturn could be seen in real time like that from the vantage point of the moons orbit. is that real? then jupiter can be seen even better since it's closer and much bigger?

[geckzilla]

Yeah, Juan. You can easily find many examples of Jupiter behind the moon. You can just barely make out Jupiter's moons sometimes, too. Occultations and transits are not only scientifically useful but they also give dimension to otherwise flat-looking space.

[JuanAustin]

thanks!

[BMAONE23]

The Moon Eclipses Saturn

Reminds me of my Avatar

[hlwelborn]

Extra cool.

[Glenriven]

That is an awesome photo.

[Virgil S.]

Well, I want to say thank you twice: first to the guys at APOD for posting yet another cool picture, second to Nitpicker above for a nice clear answer to a question that occurred to me immediately (and to Internet, for a moment at least, also). I agree with Deric's comment above, as well.
In case anyone is interested, I did a non-careful calculation based on Googled data and found
angle subtended by sun at location of Saturn = 9.7E-4 rad
angle subtended by Moon at location of Saturn = 2.7E-6 rad
-over 100 times smaller - so our lovely Moon just can't cast a shadow - at least not one with an umbra, and not a noticeable one - on Saturn. It is too small and too far from Saturn.
Comment for JuanAustin - unless I am seriously mistaken, no photo of Saturn from the vantage point of the Moon's orbit was shown - the vantage point was Buenos Aires.

[neufer]

I did a non-careful calculation based on Googled data and found

• angle subtended by sun at location of Saturn = 9.7E-4 rad
  angle subtended by Moon at location of Saturn = 2.7E-6 rad

-over 100 times smaller - so our lovely Moon just can't cast a shadow - at least not one with an umbra, and not a noticeable one - on Saturn.

[b][color=#0000FF][i]An Introduction to Solar System Astronomy[/i] by Prof. Richard Pogge[/color][/b]

---

However, when our lovely Moon does cast its penumbral shadow on Saturn then, probably, so does the Earth itself
... and that should be noticeable from space:

<<In terms of photometric performance, Kepler is working well. The objective was a combined differential photometric precision of 20 parts per million (PPM) on a magnitude 12 star for a 6.5 hour integration. This estimate was developed allowing 10 ppm for stellar variability, roughly the value for the Sun. The signal (at infinity) from an Earth-size planet is 80 ppm.>>

[pkoen]

Here is my capture of the occultation of Saturn on 4 August 2014 from Adelaide South Australia.

Taken with a ZWO ASI120MC astronomical video camera through a Meade ETX90 telescope. Stack of 212 frames of Saturn and 133 frames of the Moon.