Acceleration of Coronal Mass Ejection Plasma in the Low Corona as Measured by the Citizen CATE Experiment

The citizen Continental-America Telescopic Eclipse (CATE) Experiment was a new type of citizen science experiment designed to capture a time sequence of white-light coronal observations during totality from 17:16 to 18:48 UT on 2017 August 21. Using identical instruments the CATE group imaged the inner corona from 1 to 2.1 RSun with 1 43 pixels at a cadence of 2.1 s. A slow coronal mass ejection (CME) started on the SW limb of the Sun before the total eclipse began. An analysis of CATE data from 17:22 to 17:39 UT maps the spatial distribution of coronal flow velocities from about 1.2 to 2.1 RSun, and shows the CME material accelerates from about 0 to 200 km s−1 across this part of the corona. This CME is observed by LASCO C2 at 3.1–13 RSun with a constant speed of 254 km s−1. The CATE and LASCO observations are not fit by either constant acceleration nor spatially uniform velocity change, and so the CME acceleration mechanism must produce variable acceleration in this region of the corona

Sky Brightness at Zenith During the January 2019 Total Lunar Eclipse

Lunar eclipses occur during the full moon phase when the moon is obscured by Earth’s shadow. During these events, the night sky brightness changes as the full moon rises and then passes first into the penumbral and then the umbral shadow. We acquired sky brightness data at zenith using a Unihedron Sky Quality Meter during the 20–21 January 2019 total lunar eclipse as seen from Morehead, Kentucky. The resulting sky brightness curve shows an obvious signature when the moon enters the umbral (partial) eclipse phases and the total eclipse phase. During the total eclipse phase, the brightness curve is flat and measures 19.1 ± 0.1 mag / arcsec2. The observed brightness at totality is close to typical new moon in January night at our location, which measures 19.3 ± 0.1 mag / arcsec2. The partial eclipse phase is symmetric on either side of totality. The penumbral phase is more difficult to identify in the plot, without comparison to a typical full moon night. There is a clear asymmetry in the curve just before and just after the umbral phase. This asymmetry is probably due to changes in terrestrial atmospheric conditions, such as high altitude clouds

Estimating the size of Earth’s umbral shadow using sky brightness light curves during a lunar eclipse

We present a simple method to estimate the size of Earth’s umbral shadow in a classroom setting. The method uses the published sky brightness curves obtained during a total lunar eclipse and requires only a conceptual understanding of lunar eclipses and simple geometric considerations. It is suitable for use in introductory and upper level astronomy courses

Worldwide variations in artificial skyglow

Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope, and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ~5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program

Contemporaneous Observations of Direct and Raman Scattered O VI in Symbiotic Stars

Symbiotic stars are binary systems consisting of a hot star, typically a white dwarf, and a cool giant companion. The wind from the cool star is ionized by the radiation from the hot star, resulting in the characteristic combination of sharp nebular emission lines and stellar molecular absorption lines in the optical spectrum. Most of the emission lines are readily identifiable with common ions. However, two strong, broad emission lines at $\lambda\lambda$ 6825, 7082 defied identification with known atoms and ions. In 1989 Schmid made the case that these long unidentified emission lines resulted from the Raman scattering of the O VI resonance photons at $\lambda\lambda$ 1032, 1038 by neutral hydrogen. We present contemporaneous far-UV and optical observations of direct and Raman scattered O VI lines for nine symbiotic stars obtained with the Hopkins Ultraviolet Telescope (Astro-2) and various ground-based telescopes. The O VI emission lines are present in every instance in which the $\lambda\lambda$ 6825, 7082 lines are present in support of the Schmid Raman scattering model. We calculate scattering efficiencies and interpret the results in terms of the Raman models. Additionally, we measure the flux of the Fe II fluorescence line at $\lambda$1776, which is excited by the O VI line at $\lambda$1032, and calculate the first estimates of the conversion efficiencies of this process.Comment: 48 pages, 5 figure

Demonstrating Fluorescence with Neon Paper and Plastic

An article written by Jennifer J. Birriel and Clarissa Roe and published in the August 2015 issue of The Physics Teacher, pages 328-329

Period and pulse duration with “strobe” lights

Strobe lights have traditionally been discussed in The Physics Teacher in the context of stop action strobe photography. During the Halloween season most department and hardware stores sell inexpensive, compact “strobe” lights. These lights generally sell for under $10 and usually employ LED lights. Most such devices have a rotary switch to adjust the rate at which the LED bulbs flash. This rotary switch is not calibrated—i.e., it has no markings to indicate the rate, but in general the greater the rotation of the switch from the off position, the faster the rate of flashing. We show how these simple devices can be used with a light sensor to study both the frequency of flashing and the duration of the light pulse. We briefly discuss if these devices are truly strobe lights