Starship Asterisk*

MargaritaMc wrote:Gosh. That is SO skilful, alter-ego. And SO helpful.

Anthony Barreiro wrote: That is really helpful. I've been looking at this beautiful apod repeatedly since yesterday, and I'm seeing the motion of Mercury passing between the Earth and Sun. You can't see this movement at a point in time, and even building up a mental picture through repeated observations is much less vivid and immediate than this image. Thanks imagers!

 

alter-ego wrote: I've created two composites simulating the Mercury composite today. The location is Spain, and date range is Feb 1 to Feb 25, 2000. The green region is a fake semitransparent ground (W = West in the base image). The base image is for a fixed horizon, and you can see the motion of the Sun along a line 10° below the horizon. The hover image is the same date range, but the sun is fixed, also at 10°below the horizon (i.e. horizon moves). I've left off the "W" in this image. You can see that the bulk of Mercury's motion along the horizon is do to the Sun's relative motion. The hover image does show that a little less than half of the planet's motion along the horizon is relative to the Sun. I believe this is a reasonable representation.

Chris Peterson wrote:

DavidM wrote:Do the nightly positions of Mercury take into account the gradual westward movement of the Sun at sunset? In other words, are we seeing positions of Mercury relative to the mountain backdrop, or relative to the setting sun?

I'd say, to a first approximation, the vertical movement is relative to the Sun, but the horizontal is relative to the horizon. The time of each shot seems to have been determined by fixing the distance of the Sun below the horizon, so the image reflects the drift in sunset position over the time series.

DavidM wrote:Do the nightly positions of Mercury take into account the gradual westward movement of the Sun at sunset? In other words, are we seeing positions of Mercury relative to the mountain backdrop, or relative to the setting sun?

Boomer12k wrote:... .
Here is a photo of the east end of our street, from my driveway, where I do my Astronomy. Poor as it is. The red dot is where Mercury was in my shot, maybe a tad lower. (May not be exact. But you get the idea.) And the dot is over-sized for emphasis. The Yellow dot is where I saw it the first time through my scope. ... .

I also do not have the luxury of taking my 100 pound scope and dolly in my 240 Z, out to a deserted location. Not happening. So, you can see I don't live at the top of Mauna Kea, and Mt. Palomar was taken.

...

Clear Skies, and unobstructed views, everyone!!! Space telescopes are the BEST!!!!

:---[===] *

Anthony Barreiro wrote:

Boomer12k wrote:Or, if you have a computerized telescope you can get a shot of Mercury even through the branches of the trees at the end of the street! If you're LUCKY!

Shot was early morning, just before sunrise. Actually this one was above the trees, barely. This was the SECOND time I had ever SEEN MERCURY, both were with my 10" Meade. A bright, fiery red dot. Even knowing where it was, I could not find it with my 10 power binoculars. Very difficult even with computer controls, as it is not totally centered when the scope finds it. So, you have to hunt a little bit. But worth the wait...

Click on the picture, then click again for close up, and you can see the PHASE. Picture should actually be flipped horizontally for proper view, the sun was low to the left. It was early August 2012. My focus also isn't very good, and the atmosphere interferes too.

The picture looks dark, but the sky was actually early dawn.

:---[===] *

Boomer, you're probably going to have better luck finding Mercury with a computerized scope during dawn apparitions than evening apparitions. My go-to scope needs two bright stars for alignment before it can find planets. In the evening Mercury will be setting and low toward the horizon by the time the stars come out, whereas in the morning if you get up before dawn you can align your scope and wait for Mercury to rise.

As Joe and Chris said, I find it pretty easy to see Mercury with binoculars and naked-eye during decent apparitions (although unlike Joe I don't even try to see poor apparitions). The most important thing is to find someplace with an unobstructed horizon -- my local hilltop park works well. And you need to look at the right time. For evening apparitions get out around sunset and start scanning, you'll see Mercury within 30 minutes. In the morning start looking around Mercury's predicted rising time, and again you should be able to see Mercury within 30 minutes or so. In either the morning or the evening you'll get the best view when Mercury is highest in the sky: as soon as possible in the evening, and as late as possible in the morning.

Given the amount of atmospheric distortion during Mercury's low appearances, I find I get a steadier view through a smaller aperture telescope. In my 70 mm refractor at 50x magnification, when the atmosphere is relatively steady I can see Mercury's phase.

Boomer12k wrote:Or, if you have a computerized telescope you can get a shot of Mercury even through the branches of the trees at the end of the street! If you're LUCKY!

Shot was early morning, just before sunrise. Actually this one was above the trees, barely. This was the SECOND time I had ever SEEN MERCURY, both were with my 10" Meade. A bright, fiery red dot. Even knowing where it was, I could not find it with my 10 power binoculars. Very difficult even with computer controls, as it is not totally centered when the scope finds it. So, you have to hunt a little bit. But worth the wait...

Click on the picture, then click again for close up, and you can see the PHASE. Picture should actually be flipped horizontally for proper view, the sun was low to the left. It was early August 2012. My focus also isn't very good, and the atmosphere interferes too.

The picture looks dark, but the sky was actually early dawn.

:---[===] *

Joe Stieber wrote:It was stationary at Greatest Eastern Elongation on February 14, 2000.

BDanielMayfield wrote:

jim herbert wrote:
Where in the path is Mercury moving directly, and where is it moving retrograde? Remember that the writer is not an astronomer.

I'm not an astronomer either Jim, but I don't think that planets interior to the earth (Mercury and Venus) ever move in a retrograde direction because they move faster than than the earth in their orbits around the sun. Exterior planets (Mars and beyond) preform apparent retrograde loops when the earth passes these slower movers.

http://en.wikipedia.org/wiki/Apparent_retrograde_motion wrote:
<<Though [the Sun, Moon,] all stars and planets appear to move from east to west on a nightly basis in response to the rotation of Earth, [the Sun, Moon, and] planets generally drift slowly eastward relative to the stars. This motion is normal and so is considered direct motion. However, since Earth completes its orbit in a shorter period of time than the planets outside its orbit, it periodically overtakes them, like a faster car on a multi-lane highway. When this occurs, the planet being passed will first appear to stop its eastward drift, and then drift back toward the west. Then, as Earth swings past the planet in its orbit, it appears to resume its normal motion west to east.

Inner planets Venus and Mercury appear to move in retrograde [vis-a-vis the background stars] in a similar mechanism, but as they can never be in opposition to the Sun as seen from Earth, their retrograde cycles are tied to their lower conjunctions with the Sun. >>

MargaritaMc wrote:I have severe difficulty in picturing how what is happening, as described by Joe above, relates to what we see in the Apod. I have a kind of perceptional glitch, I think. :?

Joe Stieber wrote..If it is indeed an evening picture, then Mercury would be in direct motion starting in the lower-left as it draws away from superior conjunction on January 5, 2000. It was stationary at Greatest Eastern Elongation on February 14, 2000, at the top of the hump, then in retrograde motion on the right of the right-hand side of the hump as it heads back towards the sun and inferior conjunction on March 1, 2000.

jim herbert wrote:Where in the path is Mercury moving directly, and where is it moving retrograde? Remember that the writer is not an astronomer.

jim herbert wrote:I'm a long-time APOD fan, but no astronomer, so please bear with an inexpert question: Is the time sequence from left to right, or the reverse? I am assuming the former. Here's another, more fun question: Where in the path is Mercury moving directly, and where is it moving retrograde? Remember that the writer is not an astronomer.

http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=1095 wrote:

Click to play embedded YouTube video.

<<This colorful view of Mercury was produced by using images from the color base map imaging campaign during MESSENGER's primary mission. These colors are not what Mercury would look like to the human eye, but rather the colors enhance the chemical, mineralogical, and physical differences between the rocks that make up Mercury's surface.

Young crater rays, extending radially from fresh impact craters, appear light blue or white. Medium- and dark-blue areas are a geologic unit of Mercury's crust known as the "low-reflectance material", thought to be rich in a dark, opaque mineral. Tan areas are plains formed by eruption of highly fluid lavas. The crater whose rays stretch across the planet is Hokusai. The giant Caloris basin is the large circular tan feature.>>

Joe Stieber wrote:I think the difficulty in finding Mercury is greatly overstated, to the point that a lot of folks don’t even try.