High-resolution Satellite Imaging of the 2004 Transit of Venus and Asymmetries in the Cytherean Atmosphere

This paper presents the only space-borne optical-imaging observations of the 2004 June 8 transit of Venus, the first such transit visible from Earth since AD 1882. The high-resolution, high-cadence satellite images we arranged from NASA's Transition Region and Coronal Explorer (TRACE) reveal the onset of visibility of Venus's atmosphere and give further information about the black-drop effect, whose causes we previously demonstrated from TRACE observations of a transit of Mercury. The atmosphere is gradually revealed before second contact and after third contact, resulting from the changing depth of atmospheric layers refracting the photospheric surface into the observer's direction. We use Venus Express observations to relate the atmospheric arcs seen during the transit to the atmospheric structure of Venus. Finally, we relate the transit images to current and future exoplanet observations, providing a sort of ground truth showing an analog in our solar system to effects observable only with light curves in other solar systems with the Kepler and CoRoT missions and ground-based exoplanet-transit observations

Temporal Correlation Between Outbursts and Fragmentation Events of Comet 168P/Hergenrother

Outbursts are known to begin with a sudden appearance and steep brightening of a "stellar nucleus" --- an unresolved image of a plume of material on its way from the comet's surface and an initial stage of an expanding halo of ejecta. Since the brightness of this feature is routinely reported, together with astrometry, by most comet observers as the "nuclear magnitude," it is straightforward to determine the onset time, a fundamental parameter of any outburst, by inspecting the chronological lists of such observations for a major jump in the nuclear brightness. Although it is inadmissible to mix nuclear magnitudes by different observers without first carefully examining their compatibility, the time constraints obtained from data sets reported by different observers can readily be combined. The intersection of these sets provides the tightest possible constraint on the outburst's onset time. Applied to comet 168P/Hergenrother during its 2012 return to perihelion, three outbursts were detected and their timing determined with good to excellent accuracy. Six fragmentation events experienced by the comet are shown to have occurred in the same period of time as the outbursts. Three companions are likely to have broken off from the primary in the first outburst, two companions in the second outburst, and one companion in the last outburst. All companions were short-lived, belonging to the class of excessively brittle fragments. Yet, the results suggest that most of the mass lost in the first outburst remained relatively intact during the liftoff, while the opposite was the case in the last outburst.Comment: 24 pages, 12 tables, 3 figures; to appear in the International Comet Quarterl

Traditions connected with the pole shift model of the Pleistocene

As is well known, during the Last Glacial Maximum, about 20'000 years ago, the ice was asymmetrically distributed around the present North Pole. It reached the region of New York, while east Siberia remained ice free. Mammoths lived in arctic regions of east Siberia, where now their food cannot grow. Therefore the globe must have been turned in such a way that the North Pole was in Greenland. The required rapid geographic pole shift at the end of the ice ages has been shown to be physically possible, on condition that an astronomical object of planetary size in an extremely eccentric orbit existed. In this postulated situation it was red hot and a disk shaped gas cloud reduced the solar radiation on Earth in a time dependent way. A frequent objection to this hypothesis is that the phenomena should be reported in old traditions. This paper quotes such traditions from passages of Platon, Herodotus, Ovid, papyrus Ipuwer, Gilgamesh, the Bible, American Indians and other civilizations. Far from being exhaustive the examples show that apparently strange traditions can report observed facts. This connection is of mutual benefit for science and humanities

Formation and dissolution of leaky clusters

Massive Galactic clusters (> 1000 Msun) exhibit a clear correlation between cluster density, size and age and can be sorted in two categories, i.e. starburst and leaky clusters. The reason for the existance of two types of massive clusters is an open question. However, the answer is probably connected to a different formation histories of the two types. In this study we concentrate onleaky clusters only and investigate possible formation scenarios and gas expulsion phase. This is done by using existing observational data and numerical results of embedded cluster properties. Assuming that a clear correlation between cluster density, size and age exists, it is shown that the density-radius development over time forembedded clusters can be approximated by rho \approx 100*r ^{-1.3} Msun pc^{-3}. The consequences for the star formation process in leaky clusters are discussed and found to favour an inside-out star formation scenario with an initially low but later accelerated star formation rate. It is shown how the leaky clusters form in a unique sequential manner and that rapid gas expulsion is responsible for the 80-90\% mass loss over the next 20 Myr.Comment: 7 pages, 4 figures, accepted by A&

Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU2_\mathrm{2}

We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU$_\mathrm{2}$ , which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU$_\mathrm{2}$ are 44.6 $\pm$ 0.5\% in the R$_\mathrm{C}$ band and 44.0 $\pm$ 0.6\% in the V band at a solar phase angle of 81.0\degr. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (< 0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU$_\mathrm{2}$ has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.Comment: 9 pages, 5 figures, and 3 tables, accepted for publication in A&

Venus cusp observations during 1969 - Synopsis of results

Venus cusp observations during 196

Impact splash chondrule formation during planetesimal recycling

Chondrules are the dominant bulk silicate constituent of chondritic meteorites and originate from highly energetic, local processes during the first million years after the birth of the Sun. So far, an astrophysically consistent chondrule formation scenario, explaining major chemical, isotopic and textural features, remains elusive. Here, we examine the prospect of forming chondrules from planetesimal collisions. We show that intensely melted bodies with interior magma oceans became rapidly chemically equilibrated and physically differentiated. Therefore, collisional interactions among such bodies would have resulted in chondrule-like but basaltic spherules, which are not observed in the meteoritic record. This inconsistency with the expected dynamical interactions hints at an incomplete understanding of the planetary growth regime during the protoplanetary disk phase. To resolve this conundrum, we examine how the observed chemical and isotopic features of chondrules constrain the dynamical environment of accreting chondrite parent bodies by interpreting the meteoritic record as an impact-generated proxy of planetesimals that underwent repeated collision and reaccretion cycles. Using a coupled evolution-collision model we demonstrate that the vast majority of collisional debris feeding the asteroid main belt must be derived from planetesimals which were partially molten at maximum. Therefore, the precursors of chondrite parent bodies either formed primarily small, from sub-canonical aluminum-26 reservoirs, or collisional destruction mechanisms were efficient enough to shatter planetesimals before they reached the magma ocean phase. Finally, we outline the window in parameter space for which chondrule formation from planetesimal collisions can be reconciled with the meteoritic record and how our results can be used to further constrain early solar system dynamics.Comment: 20 pages, 11 figures, 2 tables; accepted for publication in Icarus; associated blog article at goo.gl/5bDqG

On the co-orbital motion in the planar restricted three-body problem: the quasi-satellite motion revisited

In the framework of the planar and circular restricted three-body problem, we consider an asteroid that orbits the Sun in quasi-satellite motion with a planet. A quasi-satellite trajectory is a heliocentric orbit in co-orbital resonance with the planet, characterized by a non zero eccentricity and a resonant angle that librates around zero. Likewise, in the rotating frame with the planet it describes the same trajectory as the one of a retrograde satellite even though the planet acts as a perturbator. In the last few years, the discoveries of asteroids in this type of motion made the term "quasi-satellite" more and more present in the literature. However, some authors rather use the term "retrograde satellite" when referring to this kind of motion in the studies of the restricted problem in the rotating frame. In this paper we intend to clarify the terminology to use, in order to bridge the gap between the perturbative co-orbital point of view and the more general approach in the rotating frame. Through a numerical exploration of the co-orbital phase space, we describe the quasi-satellite domain and highlight that it is not reachable by low eccentricities by averaging process. We will show that the quasi-satellite domain is effectively included in the domain of the retrograde satellites and neatly defined in terms of frequencies. Eventually, we highlight a remarkable high eccentric quasi-satellite orbit corresponding to a frozen ellipse in the heliocentric frame. We extend this result to the eccentric case (planet on an eccentric motion) and show that two families of frozen ellipses originate from this remarkable orbit.Comment: 30 pages, 13 figures, 1 tabl

The participation of the Richmond negro in politics, 1890-1900

This short treatise on one aspect of Negro history is the result of the author\u27s pro\u27ound interest in United States history. The author\u27s personal interest in the history of the Negro in the New South contributed to the selection of this topic. The Richmond Negro by the end of the decade,1890-1900, was Virtually powerless politically and was ostracized from white society. All Negro Councilmen and Aldermen had been defeated in the May 1896 municipal elections and had been unsuccessful in regaining their seats. Thus in ten years the Negro had lost almost all political rights and witnessed the paternalistic attitude of many whites turn into Negrophobia

Optimization problems in gravitational attraction

AbstractThree types of problems in gravitational attraction are considered. In the first type, two isoperimetric ones are solved elementarily by means of a known inequality concerning integral means. In the second one, it is shown that if a homogeneous ellipsoid is divided into two measurable sets, then the gravitational attractive force between them is greatest when the two sets are hemiellipsoids formed by a plane containing the two largest principal axes. In the third one, it is shown that the motion of a free particle in a straight tunnel through a homogeneous ellipsoidal planet is simple harmonic. Furthermore, the periods achieve their maximum and minimum values when the tunnels are parallel to the largest and smallest axes, respectively