Starship Asterisk*

http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=681 wrote:
A Global View from Orbit
Release Date: October 28, 2011

Instrument: Narrow Angle Camera (NAC) and Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
Resolution: 2.5 km/pixel
Scale: Mercury's diameter is 4880 kilometers (3030 miles)
Map Projection: simple cylindrical

[This image] shows a global mosaic that covers over 99.9% of Mercury's surface! This mosaic is made primarily of MDIS images acquired as part of the surface morphology base map, which during the first six months of MESSENGER's orbital mission mapped over 98.7% of the surface with nearly 22,000 images. Variations in the morphological appearance of the surface are due to differences in the Sun illumination conditions and viewing geometries for the different images taken over those six months. In this mosaic, small gaps in the surface morphology base map have been filled by images taken as part of the color base map imaging campaign. A few remaining gaps have been filled by data obtained by a combination of Mariner 10 and MESSENGER flybys, most of which is visible near the north pole.>>

If the red pole represents the 12 o'clock position/meridian then
the folks living near the 3 o'clock & 9 o'clock position/meridians
will observe oscillating sunset/rises at perihelion.

djones wrote:
Decades ago Isaac Asimov wrote an article about Mercury that stated that because of the elliptical nature of Mercury’s orbit and the slow progress of the sun through its sky, there would be times where the sun appeared to go retrograde. He noted that at certain places on the surface, each day would have two sunrises and two sunsets. At sunrise it peeks over the horizon and then goes back down to be followed by a second sunrise. That evening, it would set, reemerge and then set again. Was Isaac using old data or is this still true?

djones wrote:Decades ago Isaac Asimov wrote an article about Mercury that stated that because of the elliptical nature of Mercury’s orbit and the slow progress of the sun through its sky, there would be times where the sun appeared to go retrograde. He noted that at certain places on the surface, each day would have two sunrises and two sunsets. At sunrise it peeks over the horizon and then goes back down to be followed by a second sunrise. That evening, it would set, reemerge and then set again. Was Isaac using old data or is this still true?

elipongo wrote:
The link from the word "meridian" leads to Wikipedia's article on the Hun Kal crater. The article states that the crater is the reference point for Mercury's longitude coordinate system, but that it was defined as 20 degrees West because the "actual" Prime Meridian was in shadow at the time of Mariner 10's visit. Since selecting a prime meridian is an arbitrary exercise, I assume that it was based on some telescopically observed landmark predating Mariner 10 and was retained to preserve compatibility with older observations. Does anyone know what that original landmark was?

http://en.wikipedia.org/wiki/List_of_albedo_features_on_Mercury wrote:

A 1934 map showing some of Mercury's albedo features

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<<Early telescopic observations of Mercury were based on the assumption that Mercury keeps one of its faces permanently turned toward the Sun, through the mechanism of tidal locking. Although this is not true (Mercury rotates three times on its axis for every two revolutions around the Sun), when it is positioned for best viewing from Earth, the amount by which its visible face has rotated from its previous best viewing position is fairly small.

A map of Mercury made in the 1910s by astronomer Eugène Michel Antoniadi shows the following albedo features, localized by a grid in which 0° longitude is the (assumed) subsolar meridian. No certain connection has been made between these features and the topographic features viewed on Mercury by the Mariner 10 spacecraft. Mariner 10, however, imaged less than half of Mercury's surface.>>

saturn2 wrote:I think that one solar day on Mercury is of 58 Earth days.
But the astronomers says it have a new concept of solar day on Mercury.
It¨s new for me. I don´t understand.

deathfleer wrote:no mountains. I wonder how the mountains were formed on the Earth

deathfleer wrote:no mountains. I wonder how the mountains were formed on the Earth

mister T wrote:On Mercury is everyday your birthday?

or is every other year your birthyear?

NoelC wrote:So if humans were to build an outpost there perhaps it would have to be mobile, rolling across the surface, say, just following the sunset. Just warm enough, just cool enough to be comfortable.

Let's see, if it takes 176 days for each part of the surface to see the sun, that would be, at the equator... About 9525 miles in 4224 Earth hours, or about 2 and a quarter miles per hour. You could keep up with the sunset then at just about the speed of a person walking, no?

Or maybe the mobile research station could zip from site to site and spend tens or even hundreds of hours in one spot. That would leave time for research, mining needed materials...

Pull the track toward the pole and get a rather slower pace...

http://en.wikipedia.org/wiki/Mercury_%28planet%29 wrote:
<<Although the daylight temperature at the surface of Mercury is generally extremely high, observations strongly suggest that ice exists on Mercury. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102 K; far lower than the global average. Water ice strongly reflects radar, and observations by the 70 m Goldstone telescope and the VLA in the early 1990s revealed that there are patches of very high radar reflection near the poles. While ice is not the only possible cause of these reflective regions, astronomers believe it is the most likely. The icy regions are believed to contain about 10¹⁴–10¹⁵ kg of ice, and may be covered by a layer of regolith that inhibits sublimation. By comparison, the Antarctic ice sheet on Earth has a mass of about 4×10¹⁸ kg, and Mars' south polar cap contains about 10¹⁶ kg of water. The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet’s interior or deposition by impacts of comets.>>

Magrathea78 wrote:Is the color photo a TRUE color or color enhanced process.
It is surprisingly bluer than I expected for true color.

nstahl wrote:I also thought Mercury was tidally locked Orin, but according to the Wikipedia article they did radar observations in 1965 that disproved that.

longhorn_tish wrote:I have a question about the length of the Mercury Solar Day. I homeschool my children and we have been studying Mercury for the last 4 weeks. Every book we checked out from the library and even our astronomy textbook taught us that a day on Mercury was 59 earth days and a year was 88 earth days. Yet, this article and its references all say 176 earth days.

jerloe wrote:Here's my comment. How come the image on the right has already be redacted? An upside down "L" around a couple of craters?