Sky And Telescope August 2017 Pdf
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This activity is related to a Teachable Moment from Aug. The "Pi in the Sky" math challenge gives students a chance to take part in recent discoveries and upcoming celestial events, all while using math and pi just like NASA scientists and engineers. In this problem from the set , students use the mathematical constant pi to measure the approximate size of the shadow that will fall on Earth during a total solar eclipse.
- When Sky & Telescope Had No Limit
- August 2017 night sky audio guide, transcript and sky chart
- Inside the August 2018 Issue
When Sky & Telescope Had No Limit
Our experiment was performed with a much more sensitive detection system, and with better spatial resolution, than on previous occasions and eclipses , allowing fine details of quiet coronal loops and an active-region loop system to be seen.
The camera pixel size was 1. A total of images were recorded during a In the analysis, we searched particularly for short-period intensity oscillations and travelling waves, since theory predicts fast-mode magneto-hydrodynamic MHD waves with short periods may be important in quiet coronal and active-region heating. We also searched for travelling waves along some 65 coronal structures.
However, we found no statistically significant evidence in either. This negative result considerably refines the limit that we obtained from our previous analyses, and it indicates that future searches for short-period coronal waves may be better directed towards Doppler shifts as well as intensity oscillations. Despite many years of theoretical and observational investigations, the basic physical mechanism or group of mechanisms responsible for the global coronal heating remains the subject of much debate see, e.
However, the most widely recognised candidates for the dominant heating mechanism are a direct current DC type and alternating current AC type. Such local reconnections could be triggered by the random shuffling of flux-tube footpoints, forced by macroscopic motions of dense plasma in the convection layer and photosphere Levine, ; Parker, Generally, the efficiencies and occurrence of both mechanisms are defined by local plasma parameters, field topology, and the evolution of numerous small flux tubes filling the solar corona.
Numerous searches for intensity or velocity oscillations in the solar corona at low frequencies have been made. In addition, eclipse and coronagraph observations e. Porter, Klimchuk, and Sturrock, Nevertheless, an extended wavelet analysis of the data set showed some evidence of a travelling wave with frequency 0. Some 11, individual locations were examined using both classical Fourier and wavelet software; no statistically significant period, in the range 0. However, the CCD cameras employed in both the and eclipses, although state-of-the-art when manufactured in , had effectively only a ten-bit capacity giving a dynamic range of only Although much more sophisticated space instrumentation is now available than was the case for the and eclipses, it remains true that space-based imaging cadences e.
Hence there is a need to obtain high-quality, high-cadence imaging data with ground-based instruments. In addition, the solar corona is far better observed from the ground during total solar eclipses than with a ground-based coronagraph, since for the latter there remains significant atmospheric scattering of light from the solar disk.
All components were connected by a rigid optical bench installed on a SkyWatcher EQ-8 drive mounted on top of a heavy tripod. An image of the solar corona, formed by the telescope, was projected into the SECIS optical box, which consisted of a collimating lens, a pellicle beam splitter, narrow-band green-line and neutral-density filters, and two output lenses see, e.
The maximum filter transmittance was measured to be at a wavelength of The effective spatial sampling in the green-line channel was 1. The effective temporal cadence was 0. This beam passed through a neutral-density filter with transmission 6. The spatial dimensions in the white-light channel were 1.
Thus, a larger portion of the corona was imaged as compared with the green-line images. Optical components of both the direct-line and reflected paths were installed in a rigid, light-tight aluminium box, and both CCD cameras were fixed directly to the box. The spatial resolution of the white-light channel, which is nominally marginally better than that of the green-line channel, was in fact comparable, as there was slight degradation due to atmospheric seeing.
The lower frame rate of our images led to intensity levels of the emitting structures that were higher by a factor of over 50 than those obtained with the eclipse version of our instrument. This observing site was pre-selected as a region having a high probability of clear sky, and with easy access and convenient living quarters. Apart from a few trees and bushes, there were no local obstacles in front of the instrument, and the horizon was defined by the distant Rocky Mountains.
The level of solar activity on 21 August was generally low. The contrast of the green-line image is enhanced to better display the filamentary coronal structures. After delivery to the observing site, the whole system was assembled and adjusted, and the equatorial drive was aligned the night before the eclipse using stars as light sources.
The computers and monitors were protected from direct solar illumination before and after totality using the shade of the transportation container, which was also employed as our observing station.
During the days preceding the eclipse, the weather at the observing site was perfect, and forecasts for the eclipse-viewing conditions were good. On the day of the eclipse and during totality, the sky to the northwest of the observing site was partially covered with scattered clouds.
In addition, a transparent layer of fairly uniform mist was just perceptible above the observing site towards the Sun. Observations of the eclipse started just after first contact and continued until fourth contact. A pre-programmed solar tracking rate of the drive was applied. Before and after totality, the Sun was observed through a Baader filter Mylar foil to evaluate the long- and short-period stabilities of the telescope, as well as to collect flat-field and dark-current data.
Data recorded by both cameras during totality were displayed in real-time, allowing a coarse inspection of the telescope pointing. Exposure parameters selected for the green-line channel during the pre-eclipse trials on the full Moon were applied. As a result, well-exposed images of the solar corona in the green coronal line were recorded during a The unprocessed images show a rather diffuse green-line corona over the eastern limb. An electronic gain of 3. This accuracy is still considerably better by a factor of ten than for the camera used in our previous eclipse observations.
The theoretical spatial resolution of our instrument is defined by the pixel size of the camera rather than the telescope aperture. Incidentally, as with our previous observations, it was noticeable that coronal structures crossing each other resulted in enhanced intensities, as expected for optically thin plasmas.
Although a very reliable equatorial telescope mount was employed, the pointing showed small-scale imperfections, which consisted of two components. The main one was a slow drift caused by errors in an adjustment of the drive axes, while the second was random sub-pixel and quasi-stochastic variations of the pointing in both axes.
As a result, fine adjustments had to be applied to achieve stationary images, so that a photometric analysis could subsequently be applied. After dark-current subtraction and flat-fielding, two different methods for image stabilisation were applied.
Following this, we numerically shifted the images to positions consistent with the calculated expected one for the Moon with respect to the solar corona in the FoV of the camera. The second method is based on two-dimensional correlations of the sub-images of the bright coronal structures re-binned to ten-times-smaller sub-pixels, i. This method gave better stability of the resulting series of images, despite being very sensitive to, for example, the selection of the correlation fields and the image enhancements applied.
The slightly non-linear drift across the FoV shown in the first and third panel from the top was caused by the imperfect adjustment of the rotation axes of the equatorial drive. The variations of the positions were calculated using two-dimensional correlations of the observed coronal structures. Upper panels : relative translations with black lines and without red curves a general linear trend.
Lower panels : wavelet power spectra of the relative translations without the general linear trend. No high-frequency periodic translations were detected. No indications of any instrumental oscillations were found in the frequency range above 0.
To detect macroscopic displacements of the bright coronal structures viewed against the sky, we analysed series of differential images. Although the averaged images have a lower temporal resolution, their decreased noise levels enable very small differences in a time sequence to be detected.
After a thorough analysis of the differential images, we did not detect any macroscopic displacements of the observed coronal structures during the totality. Some very faint differences, barely visible on some images, are caused by under-corrected instabilities of the pointing rather than real motions of the coronal structures.
To search for any evidence of fast-mode magneto-acoustic waves travelling along coronal loops in our coronal images, we analysed variations of the local brightness measured at numerous points selected along the bright structures. The paths were selected manually, following visible coronal structures, although some were chosen that did not do this.
The selected paths appear to be representative of all visible structures. For one path in particular No. To enhance the statistical quality of the light curves, the data are smoothed using a ten-point running average. No systematic time shifts between the light curves along any path examined, and no propagating brightness variations along any path, were detected.
Magnitudes of the detected local intensity variations, calculated as ratios of a standard deviation to a mean value of the smoothed signal, were of the order of 0. Left panel : locations of the 65 paths selected to search for any fast-mode magneto-acoustic waves in the loop-like and pillar-like magnetic structures observed above the east limb during eclipse totality the arrow with N indicates solar North.
Selected paths are indicated as chains of white dots in the enhanced-contrast image of the solar corona recorded in the green line. The red arrow shows path number 25 see text. Right panel : light curves every third one is shown for clarity for points along the path. The lowest signals are for the points farthest from the limb. The data are smoothed using a ten-point temporal running average, while the contrast of the coronal image is numerically enhanced. Short-period variations of coronal emission in the green line were searched for in the bright coronal structures, and within the entire FoV of the instrument.
To detect short-lived periods of local oscillations, as well as search for a broad spectrum of frequencies, starting from 1. Wavelet power spectra were calculated for numerous points located along randomly selected paths, following obvious loop-like coronal structures. The wavelet power spectrum is over-plotted with the cone of influence, i. Left panel: an enhanced image of the corona with over-plotted path, and the analysed pixel marked with a white dot and labelled A the arrow with N indicates solar North.
Right panels : upper variations of the measured signal in point A; middle left the wavelet power spectrum with an over-plotted cone of influence; middle right global power vs.
These always had low signal levels, and it is clear that the apparent rapid variations can invariably be attributed to noise. Wavelet analysis is resistant to variations in the mean signal level. The clipped time series become shorter, but with a uniform signal level. Once again, we found no obvious evidence of periodicities within coronal structures in these regions. From the foregoing, wavelet analysis shows that any apparent periodicities from locations along coronal features have only marginal significance.
We made an additional search for periodic behaviour in pixels regardless of whether they are along specific coronal structures. Some , pixels were examined in this way using intensity measurements, one for each image taken. Wavelet spectra were calculated for 71 frequencies from 1. A more detailed analysis of the maps involves a four-dimensional data cube, with dimensions of two space, one time, and one frequency, with a practically unlimited number of time spans.
Their random distribution, without any alignment to particular coronal structures, shows clearly that they have no physical significance.
All maps were examined by eye in the same way but only random distributions of apparent detections were found, uncorrelated with coronal structures. The arrow with N indicates solar North.
August 2017 night sky audio guide, transcript and sky chart
Ever since people first wandered the Earth, great significance has been given to the celestial objects seen in the sky. Throughout human history and across many different cultures, names and mythical stories have been attributed to the star patterns in the night sky, thus giving birth to what we know as constellations. When were the first constellations recorded? Archaeological studies have identified possible astronomical markings painted on the walls in the cave system at Lascaux in southern France. It is thought that the Pleiades star cluster is represented alongside the nearby cluster of the Hyades. Was the first ever depiction of a star pattern made over seventeen millennia ago?
To help you learn about the southern night sky, Sydney Observatory provides an audio guide, transcript of that audio, and a sky map or chart each month. Mel suggests stars and constellations to look out for this month include Scorpius, with the red star at its heart, Antares; Sagittarius which looks more like a teapot than a centaur ; Crux — more commonly known as the Southern Cross; and Ophiuchus, the 13th sign of the zodiac! Mel also tells us the best times and dates to see the planets Venus, Saturn, Jupiter and Mercury. We provide an August night sky chart PDF which shows the stars, constellations and planets visible in the night sky from anywhere in Australia. Read the Guide Hello and welcome to the night sky guide for August. Before we start our night sky tour, make sure you download the August sky map from our website. Remember that the Sun rises in the east, moves through the northern sky during the day and sets in the west or a small compass will also point you in the right direction.
You can unsubscribe anytime. America's Eclipse: One Year Later. Learn about the results of research done during the Moon's transit across the Sun. Discover how a planet-scale smash managed to make a moon so like Earth. Explore the planetary nebulae within the celestial Eagle, Aquila. Visit an Hawaiian mountaintop for a stellar view.
In the August issue of Sky & Telescope, we look back on last August's eclipse. Learn about Total solar eclipse of August Few natural Sky & Telescope / Sean Walker Dear Greg, We are looking into the PDF download issue.
Inside the August 2018 Issue
On 23 Feb. The video of this Duologue is available on this YouTube page. The intent of the publisher is to show that Nature is " fully committed to open research and the benefits this brings for researchers, institutions, funders and the wider public. Hybrid journals operate on a subscription basis, but provide researchers with the opportunity to make their individual articles OA for a fee. They emphsize their commitment to OA, but focus on the in their view continued need for hybrid journals i.
Phone or email. Don't remember me. The readers page. Le coin des lecteurs. All posts 12,
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