<p> On August 21, 2017 a total solar eclipse occurred over the United States commencing on the west coast moving across to the east coast providing an opportunity to observe how the rapid day-night-day transition changed the ionosphere&rsquo;s D-region electron density and how very low frequency (VLF) electromagnetic wave propagation was affected. To observe the solar obscurity effects, VLF receivers were deployed in two locations: one in the path of totality in Lakeside, Nebraska and another south of the totality path in Hugo, Colorado. The locations were chosen to achieve an orthogonal geometry between the eclipse path and propagation path of U. S. Navy VLF transmitter in North Dakota, which operates at 25.2 kHz and has call sign NML. VLF amplitude and phase changes were observed in both Lakeside and Hugo during the eclipse. A negative phase change was observed at both receivers as solar obscuration progressively increased. The observed phase changes became positive as solar obscuration reduced. The opposite trend was observed for the amplitude of the transmitted signal: growth as max totality approached and decay during the shadow&rsquo;s recession. The Long Wave Propagation Capability (LWPC) code developed by the US Navy was used to model the observations. LWPC is a modal solution finder for Earth-ionosphere waveguide propagation that takes into account the D-region density profile. In contrast to past efforts where a single ionosphere profile was assumed over the entire propagation path, a degree of spatial resolution along the path was sought here by solving for multiple segments of length 100-200 km along the path. LWPC modeling suggests that the effective reflection height changed from 71 km in the absence of the eclipse, to 78 km at the center of the path of totality during the total solar eclipse and is on agreement with past work.</p><p>

It is generally believed that molecular clouds are clumpy. In clumpy molecular clouds the large scale spatial distribution of the emission from the ionized, neutral, and molecular carbon species is significantly different than it would be in a cloud with a smooth density distribution. Thus it should be possible to derive some general properties of the clumps (i.e. size, volume filling factor, kinematics, etc.) by observing these species, even if individual clumps are not spatially resolved. We have built a receiver capable of observing both the J = 3 $\to$ 2 transition of $\sp{12}$CO and $\sp{13}$CO and the $\sp3$P$\sb1$ $\to$ $\sp3$P$\sb0$ transition of neutral atomic carbon, and a filterbank of novel design that acts as its backend. We have used this instrument to obtain a map of $\sp{12}$CO J = 3 $\to$ 2 in the Orion A region. The observed line shapes, and a comparison of the intensity of this line to that of the J = 1 $\to$ 0 transition, strongly suggests that this region is clumpy, that a kinetic temperature gradient exists within each clump, and that the source of the heating is situated on the surface of the cloud. Furthermore, an analysis of the smoothness of very high signal-to-noise $\sp{12}$CO and $\sp{13}$CO J = 1 $\to$ 0 spectra in the region indicates that the volume filling factor of the clumps increases from the surface to the core of the cloud. We develop a model of an edge-heated clumpy molecular cloud that takes into account the chemical and thermal effects of the UV photons on the density and temperature structure of the clumps. We show that this model can reproduce the observed $\sp{12}$CO intensities and line ratios in the region, and is in qualitative agreement with other characteristic features observed in this and other similar regions (i.e. widespread presence of warm CO, of neutral carbon, and of high dipole moment species). We discuss the implications of these results on the general properties of the clumps in the Orion region.