The Role of Radioactive Isotopes in Astrophysics
... isotopes create isotopes that can undergo beta decay. Most do so quickly in comparison with the time required to capture another neutron, but some key branch points are slow to decay. B2 FH had inventively shown that such competition at branch points could, when compared with the actual solar abunda ...
... isotopes create isotopes that can undergo beta decay. Most do so quickly in comparison with the time required to capture another neutron, but some key branch points are slow to decay. B2 FH had inventively shown that such competition at branch points could, when compared with the actual solar abunda ...
Dark Matter, Dark Energy, and the Fate of the Universe
... Dark Matter in the Milky Way In Chapter 15, we saw how the Sun’s motion around the galaxy reveals the total amount of mass within its orbit. We can similarly use the orbital motion of any other star around the galaxy to measure the mass of the Milky Way within that star’s orbit. In principle, we co ...
... Dark Matter in the Milky Way In Chapter 15, we saw how the Sun’s motion around the galaxy reveals the total amount of mass within its orbit. We can similarly use the orbital motion of any other star around the galaxy to measure the mass of the Milky Way within that star’s orbit. In principle, we co ...
Observations of Jets and Outflows from Young Stars
... ture. The YSO accelerates a wind, sometimes collimated into a jet, with a velocity several times the escape-speed from the launch region, which can range from 100 to over 500 km s−1 . Internal shocks form where faster ejecta overrun slower material. The very fastest shocks can sometimes be detected ...
... ture. The YSO accelerates a wind, sometimes collimated into a jet, with a velocity several times the escape-speed from the launch region, which can range from 100 to over 500 km s−1 . Internal shocks form where faster ejecta overrun slower material. The very fastest shocks can sometimes be detected ...
Gamma-Ray Pulsars - INTEGRAL
... ∼ 103 in some) are accelerated in the gap regions and propagate along the magnetic field. Radiation losses due to magnetic bremsstrahlung (synchro-curvature radiation) and inverse Compton scattering on a low energy photon environment counterbalance the acceleration. If the energies in the particle/p ...
... ∼ 103 in some) are accelerated in the gap regions and propagate along the magnetic field. Radiation losses due to magnetic bremsstrahlung (synchro-curvature radiation) and inverse Compton scattering on a low energy photon environment counterbalance the acceleration. If the energies in the particle/p ...
Introduction to Dark Matter
... Apart from these methods, gravitational lensing – i.e. the effects associated with the gravitational deflection of light – has also played an important role in the study of dark matter. The notion that gravity can bend rays of light was proposed already by Newton, although the magnitude of this effe ...
... Apart from these methods, gravitational lensing – i.e. the effects associated with the gravitational deflection of light – has also played an important role in the study of dark matter. The notion that gravity can bend rays of light was proposed already by Newton, although the magnitude of this effe ...
X. Nuclear star clusters in low-mass early-type galaxies
... At faint magnitudes, the dominant noise is a combination of the readnoise and the sky background noise with a small contribution of Poisson noise from the host galaxy (see also Section 4.3 and Fig. 6). For a host galaxy absolute magnitude MF814W = −13 mag, the difference between the host galaxy magn ...
... At faint magnitudes, the dominant noise is a combination of the readnoise and the sky background noise with a small contribution of Poisson noise from the host galaxy (see also Section 4.3 and Fig. 6). For a host galaxy absolute magnitude MF814W = −13 mag, the difference between the host galaxy magn ...
April 2015 Astronomy Calendar by Dave Mitsky
... Information on Iridium flares and passes of the ISS, the Tiangong-1, the USAF’s X-37B, the HST, and other satellites can be found at http://www.heavens-above.com/ The Moon is 11.6 days old, is illuminated 89.3%, and is located in Leo at 0:00 UT on April 1st. It's at its greatest northern declination ...
... Information on Iridium flares and passes of the ISS, the Tiangong-1, the USAF’s X-37B, the HST, and other satellites can be found at http://www.heavens-above.com/ The Moon is 11.6 days old, is illuminated 89.3%, and is located in Leo at 0:00 UT on April 1st. It's at its greatest northern declination ...
The Origin of Comets and the Oort Cloud
... ejected by violent whirlwinds into parabolic orbits Comets are interstellar objects: vapours ejected from stars Comets are gravitating solar-system objects; akin to planets Comets akin to planets; formed as part of solar system through collision of a comet with the Sun Nebular Hypothesis: comets, li ...
... ejected by violent whirlwinds into parabolic orbits Comets are interstellar objects: vapours ejected from stars Comets are gravitating solar-system objects; akin to planets Comets akin to planets; formed as part of solar system through collision of a comet with the Sun Nebular Hypothesis: comets, li ...
The ages of pre-main-sequence stars
... that the accreting tracks will tend to follow the zero-age mainsequence (ZAMS), and the effective pre-main-sequence life of massive stars is dominated by their early, low-mass evolution. Indeed, at higher masses the accretion time-scale becomes long compared with the nuclear time-scale, and it is di ...
... that the accreting tracks will tend to follow the zero-age mainsequence (ZAMS), and the effective pre-main-sequence life of massive stars is dominated by their early, low-mass evolution. Indeed, at higher masses the accretion time-scale becomes long compared with the nuclear time-scale, and it is di ...
THE VELOCITY DISTRIBUTION OF THE NEAREST
... The bulk flow velocity for the cluster of interstellar cloudlets within 30 pc of the Sun is determined from optical and ultraviolet absorption line data, after omitting from the sample stars with circumstellar disks or variable emission lines and the active variable HR 1099. A total of 96 velocity c ...
... The bulk flow velocity for the cluster of interstellar cloudlets within 30 pc of the Sun is determined from optical and ultraviolet absorption line data, after omitting from the sample stars with circumstellar disks or variable emission lines and the active variable HR 1099. A total of 96 velocity c ...
celestial navigation heaven`s guide for mere
... faint-looking white dwarf is what that remains after a red giant star loses its outer layers. The white dwarf will eventually lose its heat to become a cold, dark black dwarf. The neutron star, however, is a very small, super-dense star composed of mostly tightly-packed neutrons with a thin atmosphe ...
... faint-looking white dwarf is what that remains after a red giant star loses its outer layers. The white dwarf will eventually lose its heat to become a cold, dark black dwarf. The neutron star, however, is a very small, super-dense star composed of mostly tightly-packed neutrons with a thin atmosphe ...
Comprehensive search for natural satellites of Vesta by the Dawn
... contains approximately a third of the current asteroid belt by mass (e.g. O’Brien and Sykes, 2011), with Vesta being the second most massive. Vesta has a reasonably-sized SOI relative to other bodies with natural satellites, and if the conditions exist for capture or retention of ejecta from an impa ...
... contains approximately a third of the current asteroid belt by mass (e.g. O’Brien and Sykes, 2011), with Vesta being the second most massive. Vesta has a reasonably-sized SOI relative to other bodies with natural satellites, and if the conditions exist for capture or retention of ejecta from an impa ...
The Milky Way`s external disc constrained by 2MASS star counts
... Key words. Galaxy: disk – galaxie: structure – surveys ...
... Key words. Galaxy: disk – galaxie: structure – surveys ...
Rocky planetesimals as the origin of metals in DZ stars
... Farihi & Zuckerman 2009a). Thus, while there is firm observational evidence of pollution via circumstellar material, as yet there is none favouring the ISM. Aannestad et al. (1993) provided an extensive spatial, kinematical and calcium abundance analysis against which they tested likely scenarios of ...
... Farihi & Zuckerman 2009a). Thus, while there is firm observational evidence of pollution via circumstellar material, as yet there is none favouring the ISM. Aannestad et al. (1993) provided an extensive spatial, kinematical and calcium abundance analysis against which they tested likely scenarios of ...
Observational astronomy
Observational astronomy is a division of the astronomical science that is concerned with recording data, in contrast with theoretical astrophysics, which is mainly concerned with finding out the measurable implications of physical models. It is the practice of observing celestial objects by using telescopes and other astronomical apparatus.As a science, the study of astronomy is somewhat hindered in that direct experiments with the properties of the distant universe are not possible. However, this is partly compensated by the fact that astronomers have a vast number of visible examples of stellar phenomena that can be examined. This allows for observational data to be plotted on graphs, and general trends recorded. Nearby examples of specific phenomena, such as variable stars, can then be used to infer the behavior of more distant representatives. Those distant yardsticks can then be employed to measure other phenomena in that neighborhood, including the distance to a galaxy.Galileo Galilei turned a telescope to the heavens and recorded what he saw. Since that time, observational astronomy has made steady advances with each improvement in telescope technology.A traditional division of observational astronomy is given by the region of the electromagnetic spectrum observed: Optical astronomy is the part of astronomy that uses optical components (mirrors, lenses and solid-state detectors) to observe light from near infrared to near ultraviolet wavelengths. Visible-light astronomy (using wavelengths that can be detected with the eyes, about 400 - 700 nm) falls in the middle of this range. Infrared astronomy deals with the detection and analysis of infrared radiation (this typically refers to wavelengths longer than the detection limit of silicon solid-state detectors, about 1 μm wavelength). The most common tool is the reflecting telescope but with a detector sensitive to infrared wavelengths. Space telescopes are used at certain wavelengths where the atmosphere is opaque, or to eliminate noise (thermal radiation from the atmosphere). Radio astronomy detects radiation of millimetre to dekametre wavelength. The receivers are similar to those used in radio broadcast transmission but much more sensitive. See also Radio telescopes. High-energy astronomy includes X-ray astronomy, gamma-ray astronomy, and extreme UV astronomy, as well as studies of neutrinos and cosmic rays.Optical and radio astronomy can be performed with ground-based observatories, because the atmosphere is relatively transparent at the wavelengths being detected. Observatories are usually located at high altitudes so as to minimise the absorption and distortion caused by the Earth's atmosphere. Some wavelengths of infrared light are heavily absorbed by water vapor, so many infrared observatories are located in dry places at high altitude, or in space.The atmosphere is opaque at the wavelengths used by X-ray astronomy, gamma-ray astronomy, UV astronomy and (except for a few wavelength ""windows"") far infrared astronomy, so observations must be carried out mostly from balloons or space observatories. Powerful gamma rays can, however be detected by the large air showers they produce, and the study of cosmic rays is a rapidly expanding branch of astronomy.For much of the history of observational astronomy, almost all observation was performed in the visual spectrum with optical telescopes. While the Earth's atmosphere is relatively transparent in this portion of the electromagnetic spectrum, most telescope work is still dependent on seeing conditions and air transparency, and is generally restricted to the night time. The seeing conditions depend on the turbulence and thermal variations in the air. Locations that are frequently cloudy or suffer from atmospheric turbulence limit the resolution of observations. Likewise the presence of the full Moon can brighten up the sky with scattered light, hindering observation of faint objects.For observation purposes, the optimal location for an optical telescope is undoubtedly in outer space. There the telescope can make observations without being affected by the atmosphere. However, at present it remains costly to lift telescopes into orbit. Thus the next best locations are certain mountain peaks that have a high number of cloudless days and generally possess good atmospheric conditions (with good seeing conditions). The peaks of the islands of Mauna Kea, Hawaii and La Palma possess these properties, as to a lesser extent do inland sites such as Llano de Chajnantor, Paranal, Cerro Tololo and La Silla in Chile. These observatory locations have attracted an assemblage of powerful telescopes, totalling many billion US dollars of investment.The darkness of the night sky is an important factor in optical astronomy. With the size of cities and human populated areas ever expanding, the amount of artificial light at night has also increased. These artificial lights produce a diffuse background illumination that makes observation of faint astronomical features very difficult without special filters. In a few locations such as the state of Arizona and in the United Kingdom, this has led to campaigns for the reduction of light pollution. The use of hoods around street lights not only improves the amount of light directed toward the ground, but also helps reduce the light directed toward the sky.Atmospheric effects (astronomical seeing) can severely hinder the resolution of a telescope. Without some means of correcting for the blurring effect of the shifting atmosphere, telescopes larger than about 15–20 cm in aperture can not achieve their theoretical resolution at visible wavelengths. As a result, the primary benefit of using very large telescopes has been the improved light-gathering capability, allowing very faint magnitudes to be observed. However the resolution handicap has begun to be overcome by adaptive optics, speckle imaging and interferometric imaging, as well as the use of space telescopes.Astronomers have a number of observational tools that they can use to make measurements of the heavens. For objects that are relatively close to the Sun and Earth, direct and very precise position measurements can be made against a more distant (and thereby nearly stationary) background. Early observations of this nature were used to develop very precise orbital models of the various planets, and to determine their respective masses and gravitational perturbations. Such measurements led to the discovery of the planets Uranus, Neptune, and (indirectly) Pluto. They also resulted in an erroneous assumption of a fictional planet Vulcan within the orbit of Mercury (but the explanation of the precession of Mercury's orbit by Einstein is considered one of the triumphs of his general relativity theory).