Analysis of historical records of eclipses of the Sun and Moon between 720 BC and AD 1600 gives a measure of the time difference, TT − UT = ΔT. The first derivative in time along a smooth curve fitted to the values of Δ T measures the changes in the length of the day (lod). The average rate of change of the lod is found to be significantly less than that expected on the basis of tidal friction. Fluctuations on a time-scale of centuries to millennia are mainly attributed to the effects of post-glacial uplift and core-mantle coupling.

With the rapid developments in the exoplanet field, more and more terrestrial exoplanets are being detected. Characterizing their atmospheres using transit observations will become a key datum in the quest for detecting an Earth-like exoplanet. The atmospheric transmission spectrum of our Earth will be an ideal template for comparison with future exo-Earth candidates. By observing a lunar eclipse, which offers a similar configuration to that of an exoplanet transit, we have obtained a high-resolution and high signal-to-noise ratio (SNR) transmission spectrum of the Earth's atmosphere. This observation was performed with the High Resolution Spectrograph at Xinglong Station, China during the total lunar eclipse in December 2011. We compare the observed transmission spectrum with our atmospheric model, and determine the characteristics of the various atmospheric species in detail. In the transmission spectrum, O2, O3, O2 · O2, NO2 and H2O are detected, and their column densities are measured and compared with the satellites data. The visible Chappuis band of ozone produces the most prominent absorption feature, which suggests that ozone is a promising molecule for the future exo-Earth characterization. Due to the high resolution and high SNR of our spectrum, several novel details of the Earth atmosphere's transmission spectrum are presented. The individual O2 lines are resolved and O2 isotopes are clearly detected. Our new observations do not confirm the absorption features of Ca II or Na I which have been reported in previous lunar eclipse observations. However, features in these and some other strong Fraunhofer line positions do occur in the observed spectrum. We propose that these are due to a Raman-scattered component in the forward-scattered sunlight appearing in the lunar umbral spectrum. Water vapour absorption is found to be rather weak in our spectrum because the atmosphere we probed is relatively dry, which prompts us to discuss the detectability of water vapour in Earth-like exoplanet atmospheres.

The NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA), a 2.5-meter infrared telescope on board a Boeing 747-SP, will conduct 0.3 - 1,600 μm photometric, spectroscopic, and imaging observations from altitudes as high as 45,000 ft., where the average atmospheric transmission is greater than 80 percent. SOFIA's first light cameras and spectrometers, as well as future generations of instruments, will make important contributions to the characterization of the physical properties of exoplanets. Our analysis shows that optical and near-infrared photometric and spectrophotometric follow-up observations during planetary transits and eclipses will be feasible with SOFIA's instrumentation, in particular the HIPO-FLITECAM optical/NIR instruments. The airborne-based platform has unique advantages in comparison to ground- and space-based observatories in this field of research which we will outline here. Furthermore we will present two exemplary science cases, that will be conducted in SOFIA's cycle 1.

Aspects of the solar corona are still best observed during totality of solar eclipses, and other high-resolution observations of coronal active regions can be observed with radio telescopes by differentiation of occultation observations, as we did with the Jansky Very Large Array for the annular solar eclipse of 2012 May 20 in the US. Totality crossing Antarctica included the eclipse of 2003 November 23, and will next occur on 2021 December 4; annularity crossing Antarctica included the eclipse of 2008 February 7, and will next occur on 2014 April 29. Partial phases as high as 87% coverage were visible and were imaged in Antarctica on 2011 November 25, and in addition to partial phases of the total and annular eclipses listed above, partial phases were visible in Antarctica on 2001 July 2011, 2002 December 4, 2004 April 19, 2006 September 22, 2007 September 11, and 2009 January 26, and will be visible on 2015 September 13, 2016 September 1, 2017 February 26, 2018 February 15, and 2020 December 14. On behalf of the Working Group on Solar Eclipses of the IAU, the poster showed the solar eclipses visible from Antarctica and this article shows a subset (see www.eclipses.info for the full set). A variety of investigations of the Sun and of the response of the terrestrial atmosphere and ionosphere to the abrupt solar cutoff can be carried out at the future eclipses, making the Antarctic observations scientifically useful.

Background and purpose: This study examined the effect of varying the X–Y smoothing values on the average Leaf Pair Opening (LPO), MUFactor and total number of monitor units (MU) in a cohort of 20 prostate and head and neck (H&N) patients treated with dynamic intensity-modulated radiotherapy (IMRT).

Material and methods: Plans were created using Varian Eclipse™ Treatment Planning System (TPS) version 8.9.09 (Varian Medical Systems, Palo Alto, CA). Clinically approved and dosimetrically verified plans were used as a reference plans. These were re-optimised varying the X and Y smoothing parameters from 0 to 100 in various combinations.

Results: For the prostate patients, at X = 0 and Y = 0, the average LPO was 2.4 cm (σ = 0.20 cm) and 3.5 cm (σ = 0.35 cm) for X = 100 and Y = 100. For H&N, the LPO averaged over all fields increased from 1.7 cm (σ = 0.17 cm) at X = 0 and Y = 0 to 2.3 cm (σ = 0.27 cm) at X = 100 and Y = 90. The MUFactor decreased from 1.81 (σ = 0.19) at X = 0 and Y = 0 to 1.38 (σ = 0.11) at X = 100 and Y = 100 for prostates and from 1.50 (σ = 0.14) at X = 0 and Y = 0 to 1.24 (σ = 0.09) for X = 100 and Y = 90 for H&N. Total MU for prostates decreased from 1028.0 (σ = 244.6) at X = 0 and Y = 0 to 688.4 (σ = 159.3) at X = 100 and Y = 100 and from 913 (σ = 267.2) at X = 0 and Y = 0 to 696 (σ = 214.03) at X = 100 and Y = 90 for H&N.

Conclusions: Increasing smoothing decreases MUFactor, decreases total MU and increases average LPO but does not greatly enhance organs at risk (OAR) sparing. The Homogeneity Index (HI) and Paddick Conformity Index (CIPAD) appear to vary little after increasing smoothing up to approximately X = 80 and Y = 70.