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Photometry
Published in C. R. Kitchin, Astrophysical Techniques, 2020
Gravitational microlensing arises because gravity affects the paths of light beams passing near to the surface of a star. For a light (or radio, microwave, IR, UV, X-ray or γ-ray) beam just skimming the surface of the Sun, the deflection is about 1.7ʺ, and this deflection decreases as the distance of the light beam from the Sun’s surface increases. Thus, when we have a star hosting an exoplanet that, as seen from the Earth, is in front of a more distant star, the light from the latter is bent by the gravitational field of the former. Because both stars will be in relative motion with respect to the Earth, the gravitational lensing effect changes on a timescale of a few days to a few tens of days. The observed effect is that the brightness of the more distant star increases (sometimes by a factor of ten or more), as the nearer star passes between it and the Earth. If the nearer star has an exoplanet, then the gravitational field of the exoplanet will also distort the light variations of the distant star; adding brief, sharp brightening or dimming to the ‘normal’ light curve.15 Microlensing is the only (current) technique capable of detecting exoplanets outside the Milky Way galaxy. In this way, in 2018, several free-floating exoplanets were found some 1–2 Gpc away in the quasar system RX J1131-1231, which is gravitationally lensed by a closer elliptical galaxy.
Comparison of Rutherford’s atomic model with the Standard Model of particle physics and other models
Published in Journal of the Royal Society of New Zealand, 2021
In 1994 a joint decision was made to re-direct our skills in a new direction, notably the hunt for dark matter and exoplanets (known then as extra-solar planets) using the then-new technique of ‘gravitational microlensing’. The collaboration was rebranded ‘Microlensing Observations in Astrophysics’ or MOA, and moved from windswept Black Birch to the University of Canterbury Mt John Observatory in Canterbury. Thus was born the MOA project, which is described in the following section. As described later, the MOA project utilises a technique comparable to that used by Rutherford in the gold-foil experiment.