Related papers: Solar-motion correction in early extragalactic ast…
Hubble Space Telescope images of high-redshift galaxies selected via color and photometric redshifts are used to examine the size and axial-ratio distribution of galaxies as a function of redshift at lookback times t > 8 Gyr. These…
Vesto Melvin Slipher was the first astronomer to clearly define the factors that determine the "speed" of a nebular spectrograph. This brief historical summary recounts the way these ideas developed and how Slipher's early work on galaxy…
We describe calculations of the evolution of an ensemble of small planetesimals in the outer solar system. In a solar nebula with a mass of several times the Minimum Mass Solar Nebula, objects with radii of 100-1000 km can form on…
Differential rotation is a key driver of magnetic activity and dynamo processes in the Sun and other stars, especially as the rate differs across the solar layers, but also in active regions. We aim to accurately quantify the velocity at…
A new method for determining the stellar rotation period is proposed here, based on the detection of starspots during transits of an extra-solar planet orbiting its host star. As the planet eclipses the star, it may pass in front of a…
Type Ia Supernovae (SNe Ia) are widely used to measure the expansion of the Universe. To perform such measurements the luminosity and cosmological redshift ($z$) of the SNe Ia have to be determined. The uncertainty on $z$ includes an…
During the last century many observations have been made to peep into the dark matter in the universe and many astonishing behaviors of Galaxy clusters have been found which do not fit to any theories formulated before. However, Optical…
We investigate the visibility of galactic bars and spiral structure in the distant Universe by artificially redshifting 101 B-band CCD images of local spiral galaxies from the Ohio State University Bright Spiral Galaxy Survey. Our…
Assessing the significance and implications of the recently established Hubble tension requires the comprehensive identification, quantification, and mitigation of uncertainties and/or biases affecting $H_0$ measurements. Here, we…
Hubble's Law, v=HD (recession velocity is proportional to distance), is a theoretical result derived from the Friedmann-Robertson-Walker metric. v=HD applies at least as far as the particle horizon and in principle for all distances. Thus,…
Evidence from galaxy absolute magnitudes, linear diameters, and HyperLeda images is presented which strongly supports the interpretation that some normal spiral galaxies can contain large non-cosmological (intrinsic) redshifts in excess of…
I examine the interpretation of photon redshifts in curved spacetime, as being gravitational or Doppler in origin. In Friedmann-Lema\^itre-Robertson-Walker spacetime, redshifts between comoving observers are often attributed to "expanding…
On August 22, 2014, the satellites GSAT-0201 and GSAT-0202 of the European GNSS Galileo were unintentionally launched into eccentric orbits. Unexpectedly, this has become a fortunate scientific opportunity since the onboard hydrogen masers…
We discuss the stability of the photometric redshift estimate obtained with the SED fitting method with respect to the choice of the galaxy templates. Within the observational uncertainty and photometric errors, we find satisfactory…
In this article we investigate the morphology and stellar populations of high-redshift galaxies through multi-waveband HST imaging and ground-based spatially-resolved spectroscopy. We study the redshift evolution of galaxy morphology in the…
Radio galaxies can be seen out to very high redshifts, where in principle they can serve as probes of the early evolution of the Universe. Here we show that for any model of radio-galaxy evolution in which the luminosity decreases with time…
Since Edwin Hubble introduced his famous tuning fork diagram more than 70 years ago, spiral galaxies and early-type galaxies (ETGs) have been regarded as two distinct families. The spirals are characterized by the presence of disks of stars…
We present a catalog of extragalactic proper motions created using archival VLBI data and our own VLBA astrometry. The catalog contains 713 proper motions, with average uncertainties of ~ 24 muas/yr, including 40 new or improved proper…
We summarise recent Hubble Space Telescope results on the morphology of faint field galaxies. Our two principle results are: (1) the galaxies responsible for the faint blue excess have late-type/irregular morphology and (2) the number…
Sunspots are concentrations of magnetic field visible on the solar surface (photosphere). It was considered implausible that solar flares, as resulted from magnetic reconnection in the tenuous corona, would cause a direct perturbation of…