APOD: Moon and Venus Appulse over a Tree (2019 Feb 06)

[APOD Robot]

Moon and Venus Appulse over a Tree

Explanation: What's that bright spot near the Moon? Venus. About a week ago, Earth's Moon appeared unusually close to the distant planet Venus, an angular coincidence known as an appulse. Similar to a conjunction, which is a coordinate term, an appulse refers more generally to when two celestial objects appear close together. This Moon and Venus appulse -- once as close as 0.05 degrees -- was captured rising during the early morning behind Koko crater on the island of O'ahu in Hawaii, USA. The Moon was in a crescent phase with its lower left reflecting direct sunlight, while the rest of the Moon is seen because of Earthshine, sunlight first reflected from the Earth. Some leaves and branches of a foreground kiawe tree are seen in silhouette in front of the bright crescent, while others, in front of a darker background, appear white because of forward scattering. Appulses involving the Moon typically occur several times a year: for example the Moon is expected to pass within 0.20 degrees of distant Saturn on March 1.

<< Previous APOD

This Day in APOD

Next APOD >>

[Nitpicker]

Nice APOD.

According to Stellarium, the Moon will occult Saturn from Tuvalu (UT+12) in the pre-dawn skies on 2-March-2019. According to the "several times a year" link in the APOD caption, the minimum separation (which I assume is centre-to-centre) between the Moon and Saturn will be 0.18 minutes of arc, or 0.3 degrees. But it will be less than 0.25 degrees from Tuvalu, it seems.

[Boomer12k]

Awesome...and done with such aplomb...

:---[===] *

[orin stepanek]

I like it; I like it! Really nicely done by the photographer! I give it two thumbs up! I'd give it more smileys; but I think we're only allowed 3!

[neufer]

Click to play embedded YouTube video.

appulse [uh-puhls] 1620–30; < Latin appulsus driven to, landed (past participle of appellere ), equivalent to ap- ap-1 + pul- (variant stem of pellere to drive, push) + -sus, variant of -tus past participle suffix

1) energetic motion toward a point.

2) the act of striking against something.

3) Astronomy . the approach or occurrence of conjunction between two celestial bodies.

[RJN]

I am unsure what is illuminating the top part of the tree that is in front of the Earthshining Moon. This part appears distinctly white. I know it must be some sort of forward scattering, but I am unsure what type. Any thoughts from our learned asteriskians?

- RJN

[neufer]

I am unsure what is illuminating the top part of the tree that is in front of the Earthshining Moon. This part appears distinctly white. I know it must be some sort of forward scattering, but I am unsure what type. Any thoughts from our learned asteriskians?

My first question would be: if the white tree lies over the crest of the ridge
such that the lights of greater Honolulu are the illumination source?

[mjsakers]

Venus would have also been in crescent phase. This would have been good to mention, though you can't see it at this magnification and exposure. Too bad, that would look cool if you could!

[Joe Stieber]

Venus would have also been in crescent phase. This would have been good to mention, though you can't see it at this magnification and exposure. Too bad, that would look cool if you could!

Except that on the day of this appulse, 31-January-2019, Venus was in a gibbous phase, 62% illuminated.

[Nitpicker]

I am unsure what is illuminating the top part of the tree that is in front of the Earthshining Moon. This part appears distinctly white. I know it must be some sort of forward scattering, but I am unsure what type. Any thoughts from our learned asteriskians?

My first question would be: if the white tree lies over the crest of the ridge
such that the lights of greater Honolulu are the illumination source?

Could it not just be the moonlight?

It reminds me of a similar looking effect seen in the animated gif of a smoky sunset through trees, which I made and posted a few years back, here:
viewtopic.php?f=9&t=32740

At the time, I thought that the thinner parts of the foliage in the treetops, simply allowed more of the sunlight to pass through to the camera. Whether this is "forward scattering" I am not sure. It is a new term for me. But I suppose it must be.

[neufer]

I am unsure what is illuminating the top part of the tree that is in front of the Earthshining Moon. This part appears distinctly white. I know it must be some sort of forward scattering, but I am unsure what type. Any thoughts from our learned asteriskians?

My first question would be: if the white tree lies over the crest of the ridge
such that the lights of greater Honolulu are the illumination source?

Could it not just be the moonlight?

It reminds me of a similar looking effect seen in the animated gif of a smoky sunset through trees, which I made and posted a few years back, here:
viewtopic.php?f=9&t=32740

At the time, I thought that the thinner parts of the foliage in the treetops, simply allowed more of the sunlight to pass through to the camera. Whether this is "forward scattering" I am not sure. It is a new term for me. But I suppose it must be.

"Forward scattering" by airborne fog/droplets is well understood.

"Forward scattering" by leaves is not.

If it is moonlight "forward scattering" by leaves then
why doesn't the foreground kiawe tree also appear bright?

[Nitpicker]

My first question would be: if the white tree lies over the crest of the ridge
such that the lights of greater Honolulu are the illumination source?

Could it not just be the moonlight?

It reminds me of a similar looking effect seen in the animated gif of a smoky sunset through trees, which I made and posted a few years back, here:
viewtopic.php?f=9&t=32740

At the time, I thought that the thinner parts of the foliage in the treetops, simply allowed more of the sunlight to pass through to the camera. Whether this is "forward scattering" I am not sure. It is a new term for me. But I suppose it must be.

"Forward scattering" by airborne fog/droplets is well understood.

"Forward scattering" by leaves is not.

If it is moonlight "forward scattering" by leaves then
why doesn't the foreground kiawe tree also appear bright?

I speculate ...

There are typically increased amounts of water vapour within tree tops. And there are reflections off leaves, too.

The parts of the kiawe tree facing the camera, are not in direct moonlight, and I suppose insufficient moonlight managed to filter through the leaves and water vapour (by whatever means) to illuminate the parts of the tree closer to the camera.

[neufer]

There are typically increased amounts of water vapour within tree tops. And there are reflections off leaves, too.

The parts of the kiawe tree facing the camera, are not in direct moonlight, and I suppose insufficient moonlight managed to filter through the leaves and water vapour (by whatever means) to illuminate the parts of the tree closer to the camera.

The Hi-res sure looks like we are looking primarily at leaves.

While the moonlight is over-saturated, it seems like a lot of moonlight still makes it through the leaves.

[Nitpicker]

There are typically increased amounts of water vapour within tree tops. And there are reflections off leaves, too.

The parts of the kiawe tree facing the camera, are not in direct moonlight, and I suppose insufficient moonlight managed to filter through the leaves and water vapour (by whatever means) to illuminate the parts of the tree closer to the camera.

The Hi-res sure looks like we are looking primarily at leaves.

While the moonlight is over-saturated, it seems like a lot of moonlight still makes it through the leaves.

But perhaps not enough moonlight scattered/reflected by the tree, makes it through the tree to illuminate the parts of the tree facing the camera and closer to the camera. There is certainly a lot of direct moonlight getting through, as otherwise we wouldn't see any of the moon behind the tree.

[BillBixby]

While the moonlight is over-saturated, it seems like a lot of moonlight still makes it through the leaves.

But perhaps not enough moonlight scattered/reflected by the tree, makes it through the tree to illuminate the parts of the tree facing the camera and closer to the camera. There is certainly a lot of direct moonlight getting through, as otherwise we wouldn't see any of the moon behind the tree.

No scientific thought on my part here, just speculation. A flash from the camera during the exposure. Yeah, crazy idea.

[neufer]

No scientific thought on my part here, just speculation.
A flash from the camera during the exposure. Yeah, crazy idea.

The flash lit up the far tree but not the near tree

We're talking the outskirts of Honolulu here; one has to go out of their way for a dark foreground.

[Chris Peterson]

I am unsure what is illuminating the top part of the tree that is in front of the Earthshining Moon. This part appears distinctly white. I know it must be some sort of forward scattering, but I am unsure what type. Any thoughts from our learned asteriskians?

- RJN

I'm thinking we're seeing a kiawe (mesquite) tree in bloom. This is the right time of year, and they have large, light colored flower clusters at the branch tips and small leaves. They tend to flower in winter. A plumeria is also possible, although they don't usually flower in February (but they can). Both species are found at Koko Crater.

[Nitpicker]

It is hard to tell from the APOD, but I would be prepared to rule out a plumeria. And the illuminated tips of the tree look more like kiawe leaves, than kiawe flowers. I can't seem to find a daylight image of a kiawe tree in full bloom, where the yellow tone of the flowers, is significantly different from the green tone of its leaves.

I am pretty sure we have some of these in our neighbourhood. I will keep an eye out.

[neufer]

Kiawe Flower

---

I am unsure what is illuminating the top part of the tree that is in front of the Earthshining Moon. This part appears distinctly white.

I'm thinking we're seeing a kiawe (mesquite) tree in bloom. This is the right time of year, and they have large, light colored flower clusters at the branch tips and small leaves. They tend to flower in winter. A plumeria is also possible, although they don't usually flower in February (but they can). Both species are found at Koko Crater.

That works for me.

[Nitpicker]

I don't suppose the scattering effect would appear much different if the kiawe tree was in full bloom, or not. But I certainly don't think the whiter parts of the tree in the APOD are all kiawe flowers. Indeed, I think they are predominantly leaves.

[Nitpicker]

Similar effect seen here, sans flowers or leaves:

Click to view full size image

[AlexDzierba]

Hello,

Alex here, the one who shot the image of the Moon and Venus over Koko crater. The forward scattering is through the leaves of a kiawe tree. There are no plumeria trees on the rim of the crater, but there are quite a few plumerias inside the crater.

[AlexDzierba]

Hi all,

In response to the discussion regarding the forward scattering of moonlight from the kiawe leaves...

I was standing about 3/4 a mile away or so when taking this shot - and I had no flash on my camera. So, scratch that idea. Also, the leaves on those trees aren’t being illuminated by Honolulu city lights - although, those were to my back.

Usually I can see forward scattering from blades of grass, peoples’ hair, edges of cactus or tree branches, and leaves of trees just prior to the moon popping up over the Koko crater. Typically, I shoot the full moon. Since I knew there would be a close conjunction on this day, I shot a crescent moon. I overexposed the image on purpose to capture earthshine on the moon, so those tree leaves were particularly well lit up.

My Instagram page @adzierba shows many examples of my moonrise shots. I often coordinate with friends who hike up to the top.

Here are some examples of shots demonstrating forward scattering of moonlight off various objects: https://www.instagram.com/adzierba/p/Bw ... i9l9rnfuks