Lord of the Rings / Phases of the Moon II

In his fantasy masterpiece Lord of the Rings author J.R.R. Tolkein was in general consistent with real world astronomy when mentioning the phases of the moon. In a previous post A Peculiar Moon in Lord of the Rings I noted a couple of exceptions. Alas, I'm in the middle of rereading it for the zillionth time and found another glitch, this time in volume I, Fellowship of the Ring. This webpage Moon Phases in The Lord of the Rings kindly reproduces the offending passage and also sets out the relevant facts about the phases of the moon, but did not point out the inconsistency.

Above him was a black starry sky. Suddenly a pale light appeared over the crown of Weathertop behind him. The waxing moon was climbing slowly above the hill that overshadowed them, and the stars above the hill-top faded. ... ‘Look!’ said Merry. ‘The Moon is rising: it must be getting late.’

However, a waxing moon rises during the daylight hours, not at night!
Oddly enough, just a few pages earlier, while describing events taking place two nights previously, Tolkein mentioned the phase of moon accurately. “The moon was waxing, and in the early night-hours a cold grey light lay on the land.” That is correct: a waxing moon rises during the daylight hours and in the early night-hours it is still above the horizon.

Here's a speculative attempt to figure out in some detail the state of the moon the day of the incident at Weathertop - October 6 S.R. 1418. In appendix D, it says the our New Year's Day corresponds more or less to the Shire January 9. That means that the full moon - which they saw on January 8th S.R. 1419 when the Company reached Hollin - would correspond to our December 31st. There was a full moon in London on Dec 31, 1933, which can be used as a reference point. https://www.timeanddate.com/moon/phases/uk/london?year=1933

Also our 26th of September is probably a good approximation for October 6 S.R. - the date of the incident at Weathertop.

On September 26, 1933 the moon was half full and waxing https://www.timeanddate.com/moon/uk/london?month=9&year=1933.

6:52 sunrise 26th September
15:39 moonrise
18:51 sunset
22:25 moonset
6:54 sunrise 27th September, the next morning
16:23 moonrise the next afternoon

Daylight savings time was in effect during September in 1933 in England - not sure about Middle Earth on the corresponding date - but the intervals between sunrise/sunset/moonrise/moonset would not be effected.

So by that rationale, the moon would have never been above the horizon during the night of the incident at Weathertop.

Cosmography of the Local Universe

At Cosmography of the Local Universe there is a video showing the distribution and motion of the galaxies in our neighborhood. There is also an accompanying paper by Courtois, Pomar, Tully, Hoffman and Courtois. In the video "distances" are represented by velocities in km/s. It's difficult to figure out distances to galaxies directly, what we can actually measure is the "redshift" of spectral lines, which can be interpreted as a velocity, which is then assumed to also indicate distances, due to the fairly uniform expansion of our local universe. Another term appearing in the video is the 'Zone of Avoidance' or ZOA. Our own galaxy, the Milky Way, blocks our view of the galaxies, due to the the dust and stars of the Milky Way being concentrated around the plane of the Milky Way's disk. So we really don't have much information about the galaxies laying in those directions.

One of the characteristic features of the distribution of galaxies is the presence of voids: huge, roughly spherical regions in which galaxies are very sparse. I have a collection of interesting links to the literature about voids here.

The Sun is Too Round

Back in the 19th century it was observed that the orbit of Mercury deviated from the predication of Newton's law of gravity - the precession of Mercury's perihelion. One simple explanation would have been that the sun was oblate: flattened at the poles and bulging at the equator. However the sun is much too round for that to work, instead Einstein explained most of the anomaly in Mercury's orbit with a modification of Newton's gravity - his theory of General Relativity. However there was still a small discrepancy between Einstein's theory and the actual orbit of Mercury which was expected to be explained by some flattening and bulging of the sun from perfect roundness. However, the actual shape of the sun has been mighty hard to measure to the required accuracy - until recently. Alas, it appears that the sun is still rounder than expected. How Oblate Is the Sun? by Douglas Gough in Science is a review of the history of this problem and The Precise Solar Shape and Its Variability by Kuhn et. al. in the same issue is a report on recent space-based measurements.

Step up to the bar - the Milky Way bar

Apparently there's a bar/box shaped concentration of stars in the center of our Milky Way galaxy.

This central bar is oriented about 20 degrees from our line of sight to the center of the galaxy - so the diagram above doesn't look quite right to me. The bar seems to rotate like a cylinder - rigidly. This type of structure is typical of many galaxies, not just ours. There's evidence that our bar is a fairly uniform population, there's no real evidence of recent mergers. That's inconsistent with a model of galaxy formation by merger, which seemed to work well for elliptical galaxies. Our Milky Way is a barred spiral - different from ellipticals - but it was thought for a while that the central bulge of spirals might have formed a similar manner. Now that no longer appears to be true.
For some scientific details see The Bulge Radial Velocity Assay (BRAVA): II. Complete Sample and Data Release and OUR MILKY WAY AS A PURE-DISK GALAXY—A CHALLENGE FOR GALAXY FORMATION.

Type Ia Supernovae and the discovery of Cosmic Acceleration

It's not so easy to figure out the distance to far away objects in the sky - see an older post on the cosmic distance ladder. However, it's possible for even beginning astronomy students to climb the First Three Rungs of the Cosmological Distance Ladder. The top of the ladder isn't so easy though. The 2011 Nobel Prize in Physics was awarded for "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae". A key element of that discovery was the use of Type Ia supernova to determine distances. Type Ia supernova are supposed to the explosion of a white dwarf star, conveniently it seems to be possible to determine the absolute luminosity of those explosions, which indicates the actual distance.

The preprint Type Ia Supernovae and the discovery of the Cosmic Acceleration is a nice explanation of the history of this discovery by Alejandro Clocchiatti a member of one of the groups which made the discovery - the High-z Supernova Search Team.

Kepler's supernova

Spacecraft Navigation by Pulsar

Currently spacecraft find their position and velocity using radio signals sent back and forth from earth-based antennas. That's quite accurate for the components of position and velocity in the direction of earth, but in other directions the accuracy is not so good. The authors of the preprint Autonomous Spacecraft Navigation Based on Pulsar Timing Information propose using an x-ray telescope onboard the spacecraft to track the signals emitted by pulsars, which rival atomic clocks in accuracy. New models of x-ray telescopes are getting small and accurate enough to find the position and velocity of a spacecraft more accurately than an earth-based system, for interplanetary missions when the spacecraft is more than 1AU from earth.

Puzzling Star Formation Rates in Galaxies

The rate at which stars form in Galaxies is expected to decrease with time. The spectral lines in more distant galaxies are shifted to the red end of the spectrum. The light from very distant galaxies left in the distant past, so we would expect that the star formation rate in galaxies with high redshift should increase. That does not appear to be the case: On the puzzling plateau in the specific star formation rate at z=2-7

The Local Leo Cold Cloud

I've been fascinated with the Local Bubble, a region nearly empty of stars containing hot but low-density gas within the Milky Way near our Sun. Especially since it appears that the mysterious object Geminga, a radio-quiet x-ray plusar, might be the cause of this bubble. The preprint The Local Leo Cold Cloud and New Limits on a Local Hot Bubble describes a very cold cloud of gas within the Local Bubble - Curiouser and Curiouser.

Argon on Venus

There is Too much argon 40 on the moon (a recent blog post) and argon in the atmosphere of Venus is hard to understand as well. In both lunar rocks and the atmosphere of Venus the Argon 40/argon 36 ratio is 1:1 while in the atmosphere of Earth argon 40 is 99.6%.

See also 40Ar retention in the terrestrial planets and Geochemistry: Earth holds its breath in Nature 2007.

Star Clusters

Families of dynamically hot stellar systems over ten orders of magnitude in mass is a survey of star clusters in size from a few hundred to giant elliptical galaxies with a trillion stars.

Too much argon 40 on the moon

The decay of radioactive isotope potassium 40 to argon 40 is one of the main ways of finding the age of rocks: see Potassium-argon dating at Wikipedia.
But on the moon, the Apollo missions found much more argon 40 than could be explained by potassium decay. Other explanations don't look so great either, see: On the question of the 40Ar excess in lunar soils.

Globular clusters have little dark matter

Apparently globular clusters have little or no dark matter:
Evidence Against Dark Matter Halos Surrounding the Globular Clusters MGC1 and NGC 2419. This preprint also finds the motion of stars in these globular clusters is consistent with Newtonian gravity and not MOND, even though the clusters are in the low acceleration range in which MOND is supposed to make a difference. However previous see the blog post Velocities in Globular Clusters for a report that MOND does work in GCs!
Maybe globular clusters originated as the nuclear cluster of a galaxy: the preprint Nuclear Star Clusters mentions this as a possibility while discussing the star clusters at the center of galaxies.

In contrast Dwarf spheroidal galaxies are dark matter dominated.

The Gamma Ray bubbles of the Milky Way

NASA's Fermi Telescope Finds Giant Structure in our Galaxy

Here's the preprint announcing the discovery: Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?.

These bubbles are gigantic and may have been created by an episode of Galactic center activity 1-2 Mya Fermi Bubbles: Evidence for a Possible Recent AGN Jet Activity in the Galaxy.

On the other hand maybe they are really, really old! The Fermi Bubbles: Giant, Multi-Billion-Year-Old Reservoirs of Galactic Center Cosmic Rays

Ultra High Energy Cosmic Rays

Here's a nice review preprint: Ultrahigh Energy Cosmic Rays.

The Missing Satellites Problem

The standard of model of the cosmology Lambda-CDM predicts that our Milky Way galaxy should have many more satellite galaxies than we actually see: Dwarf Galaxy Problem. It could be that some are actually missing or perhaps they are fainter than expected and hard to detect. See the preprints Notes on the Missing Satellites Problem for a review and also Too big to fail? The puzzling darkness of massive Milky Way subhalos.

Modified Gravity works well for Gas Rich Galaxies

The motion of stars and gas in galaxies surprisingly is not so easily explained by the gravity they produce. They tend to follow flat rotation curves - after a certain distance the velocity tends to be the same whether a star is nearer or farther from the center of the galaxy. It had been expected that more distant stars and gas would be moving slower. The most popular explanation for this is dark matter , that 80% of the mass of galaxies like our Milky Way is some new unseen form that doesn't interact much, except by gravity. Another possible explanation is MOND, a theory that modifies gravity when it is very weak. A recent preprint shows that MOND works very well for gas-rich galaxies while dark matter is rather less natural and convincing: A Novel Test of the Modified Newtonian Dynamics with Gas Rich Galaxies.

The Downsizing Problem for Galaxies

It was commonly thought that galaxies form and grow larger by mergers of smaller masses. However, it has been observed that galaxies with high redshifts (which indicates that they are being observed at an early time) are on average larger than galaxies at low redshifts. This is the Downsizing Problem. The preprints Feedback in Galaxy Formation and The Many Manifestations of Downsizing: Hierarchical Galaxy Formation Models confront Observations discuss this and other problems in galaxy formation theory.

Polar Ring Galaxies

Polar Ring Galaxies have a large ring of material perpendicular to the main galaxy. See also Polar Disk Galaxy found in Wall between Voids.

Source: Hubblesite.org

Another Void Model of Cosmic Acceleration

Supernovae observations published in 1998 surprisingly indicated that the expansion of the universe is accelerating - with the standard explanation being Dark Energy. A very different explanation for this acceleration is the possibility that we are near the center of a gigantic void in the distribution of galaxies. Many such Voids (smaller, but still mind-bogglingly large themselves) have been found. The preprint Reconciling the local void with the CMB elaborates on earlier proposals by relaxing the assumption that the Cosmic Microwave Background (CMB) is scale-invariant.
Here's an earlier blog post on this topic: Void Models of Cosmic Acceleration.

One Way Ticket to Mars

Getting to the planet Mars isn't so difficult, as it turns out - it's coming back that's hard. Are you you willing to permanently relocate? To Boldly Go: A One-Way Human Mission to Mars discusses the possibilities.