762 research outputs found
Magnetospheric influence on the Moon\u27s exosphere
[1] Atoms in the thin lunar exosphere are liberated from the Moon\u27s regolith by some combination of sunlight, plasma, and meteorite impact. We have observed exospheric sodium, a useful tracer species, on five nights of full Moon in order to test the effect of shielding the lunar surface from the solar wind plasma by the Earth\u27s magnetosphere. These observations, conducted under the dark sky conditions of lunar eclipses, have turned out to be tests of the differential effects of energetic particle populations that strike the Moon\u27s surface when it is in the magnetotail. We find that the brightness of the lunar sodium exosphere at full Moon is correlated with the Moon\u27s passage through the Earth\u27s magnetotail plasma sheet. This suggests that omnipresent exospheric sources (sunlight or micrometeors) are augmented by variable plasma impact sources in the solar wind and Earth\u27s magnetotail
Celestial Images: Antiquarian Astronomical Charts and Maps from the Mendillo Collection
This is the catalogue of the exhibition "Celestial Images" at Boston University Art Gallery
Periodicities in the occurrence of aurora as indicators of solar variability
A compilation of records of the aurora observed in China from the Time of the Legends (2000 - 3000 B.C.) to the mid-18th century has been used to infer the frequencies and strengths of solar activity prior to modern times. A merging of this analysis with auroral and solar activity patterns during the last 200 years provides basically continuous information about solar activity during the last 2000 years. The results show periodicities in solar activity that contain average components with a long period (approx. 412 years), three middle periods (approx. 38 years, approx. 77 years, and approx. 130 years), and the well known short period (approx. 11 years)
Determinants of Usage of Age-Appropriate Child Safety Seats in Connecticut
In the United States, motor vehicle crashes are one of the leading causes of unintentional injury death and disability for children ages 1\u2715 years. Despite local, state, and federal legislative and educational efforts, children continue to be restrained improperly and thus face harm. Identifying behaviors and barriers that place child occupants at risk is crucial for implementing focused, injury-prevention programs and policies. The purpose of this study was to evaluate the effectiveness of Connecticut\u27s child passenger safety law that was strengthened in 2005. This study involved a multifactorial approach to predicting child seat use, guided by Roger\u27s diffusion of innovations as the theoretical framework. The analysis determined if there was a difference in the prevalence of car seat use before as compared to after law implementation and identified variables that best predicted the use of car seats and premature transition to a seat belt. Using Connecticut\u27s Crash Data Repository, a logistic regression analysis indicated that car seat use was 1.3 times more likely post law (OR 0.75; 95% CI: 0.65-0.86) and that in particular, children ages 4, 5, and 6 (combined) were most positively affected by the law (OR 0.67; 95% CI 0.54-0.82). Driver sex, crash time of day, child age, and child seating position were all determined to be significant predictors of whether or not a child was in a child safety seat. Additionally, these variables were also determined to be predictors of early transition to use of a lap/shoulder belt (versus child seat). The social change implication of this study is that identifying predictors of car seat use and early transition helps to formulate and implement injury prevention measures that could in turn help to decrease medical costs, save lives, and prevent injuries
Investigator Perspectives
A detailed presentation is given in the form of viewgraphs on principal investigator requirements ranging from simple to complex payloads. It is stated that the program was very important to the US science community, and that there was already concern that its funding was under stress, impacting the number of missions flown, down from around 44 to 25 or so. It is also stated that the program needs more help at NASA HQ
Scattering properties of dust in Orion and Epsilon Eridani exoplanetary system
Dust grain properties were investigated in two very different Galactic environments: the interstellar medium and an exoplanetary system. Two sounding rocket missions were developed to study these regions.
Wide-field observations of the Orion OB stellar association were performed in the far-ultraviolet using the Spectrograph for Photometric Imaging with Numeric Reconstruction (SPINR) sounding rocket. These observations reveal the diffuse signature of starlight scattering off interstellar dust grains. The spectral-imaging data were used along with a three-dimensional radiative transfer model to measure the dust scattering parameters: the grain albedo (a) and the scattering asymmetry (g). The measured parameters are consistent with previous measurements made toward Orion. A sharp increase in albedo was measured at 〜1330 A. This feature is not explained by current grain models.
The constructed three-dimensional model of Orion includes a two-component dust distribution. The foreground distribution is responsible for the small amount of visible reddening measured toward the bright stars in the Orion constellation.The background distribution represents the Orion Molecular Cloud, which dominates observations of dust emission in the infrared. This model was used to show that backscattered light from the molecular cloud alone cannot produce the observed scattered light distribution. The foreground dust, though optically thin in the visible, significantly contributes to the scattered light in the far-ultraviolet. This suggests that observations of Orion in the infrared and far-ultraviolet may probe entirely different dust populations.
The Planetary Imaging Concept Testbed Using a Rocket Experiment (PICTURE) sounding rocket was developed to characterize dust grains in the nearby Epsilon Eridani exoplanetary system. This is a young, dusty system with a Jupiter-massed planet orbiting at 〜3.4 AU (astronomical units). PICTURE sought to capture a direct, visible-light image of dust-scattered starlight in this system with the aid of a high-contrast nulling coronagraph. The design and laboratory testing of the PICTURE science payload is presented. Although the mission returned no science data, several important technological advances were made to enable future direct imaging missions. Most notably, PICTURE demonstrated 5.1 milliarcsecond pointing stability using a fast optical tracking system
Ionospheric storms at geophysically-equivalent sites – Part 2: Local time storm patterns for sub-auroral ionospheres
The response of the mid-latitude ionosphere to geomagnetic storms depends
upon several pre-storm conditions, the dominant ones being season and local
time of the storm commencement (SC). The difference between a site's
geographic and geomagnetic latitudes is also of major importance since it
governs the blend of processes linked to solar production and magnetospheric
input, respectively. Case studies of specific storms using ionospheric data
from both hemispheres are inherently dominated by seasonal effects and the
various local times versus longitude of the SCs. To explore
inter-hemispheric consistency of ionospheric storms, we identify
"geophysically-equivalent-sites" as locations where the geographic and
geomagnetic latitudes have the same relationship to each other in both
hemispheres. At the longitudes of the dipole tilt, the differences between
geographic and geomagnetic latitudes are at their extremes, and thus these
are optimal locations to see if pre-conditioning and/or storm-time input are
the same or differ between the hemispheres.
<br><br>
In this study, we use ionosonde values of the F2-layer maximum electron
density (<I>Nm</I>F2) to study geophysical equivalency at Wallops Island (VA) and
Hobart (Tasmania), using statistical summaries of 206 events during solar
cycle #20. We form average patterns of Δ<I>Nm</I>F2 (%) versus local
time over 7-day storm periods that are constructed in ways that enhance the
portrayal of the average characteristic features of the positive and
negative phases of ionospheric storms. The results show a consistency
between four local time characteristic patterns of storm-induced
perturbations, and thus for the average magnitudes and time scales of the
processes that cause them in each hemisphere. Subtle differences linked to
small departures from pure geophysical equivalency point to a possible
presence of hemispheric asymmetries governed by the non-mirror-image of
geomagnetic morphology in each hemisphere
Ionospheric effects of the solar flares of September 23, 1998 and July 29, 1999 as deduced from global GPS network data
This paper presents data from first GPS measurements of global response of
the ionosphere to solar flares of September 23, 1998 and July 29, 1999. The
analysis used novel technology of a global detection of ionospheric effects
from solar flares (GLOBDET) as developed by one of the authors (Afraimovich E.
L.). The essence of the method is that use is made of appropriate filtering and
a coherent processing of variations in total electron content (TEC) in the
ionosphere which is determined from GPS data, simultaneously for the entire set
of visible (over a given time interval) GPS satellites at all stations used in
the analysis. It was found that fluctuations of TEC, obtained by removing the
linear trend of TEC with a time window of about 5 min, are coherent for all
stations and beams to the GPS satellites on the dayside of the Earth. The time
profile of TEC responses is similar to the time behavior of hard X-ray emission
variations during flares in the energy range 25-35 keV if the relaxation time
of electron density disturbances in the ionosphere of order 50-100 s is
introduced. No such effect on the nightside of the Earth has been detected yet.Comment: EmTeX-386, 13 pages, 5 figure
The use of GPS-arrays in detecting shock-acoustic waves generated during rocket launchings
This paper is concerned with the form and dynamics of shock-acoustic waves
(SAW) generated during rocket launchings. We have developed a method for
determining SAW parameters (including angular characteristics of the wave
vector, and the SAW phase velocity, as well as the direction towards the
source) using GPS-arrays whose elements can be chosen out of a large set of
GPS-stations of the global GPS network. The application of the method is
illustrated by a case study of ionospheric effects from launchings of launch
vehicles (LV) Proton and Space Shuttle from space-launch complexes Baikonur and
Kennedy Space Center (KSC) in 1998 and 1999 (a total of five launchings). The
study revealed that, in spite of a difference of LV characteristics, the
ionospheric response for all launchings had the character of an N - wave
corresponding to the form of a shock wave, regardless of the disturbance source
(rocket launchings, industrial explosions). The SAW period T is 270--360 s, and
the amplitude exceeds the standard deviation of TEC background fluctuations in
this range of periods under quiet and moderate geomagnetic conditions by
factors of 2 to 5 as a minimum. The angle of elevation of the SAW wave vector
varies from 30 degree to 60 degree, and the SAW phase velocity (900-1200 m/s)
approaches the sound velocity at heights of the ionospheric F-region maximum.Comment: EmTeX-386, 23 pages, 6 figure
- …