at 9 p.m. on June 10 being visible during the late northern spring or the southern autumn. From the northern hemisphere, an easy way to find Arcturus is to follow the arc of the handle of the Big Dipper (or Plough). By continuing in this path, one can find Spica, "Arc to Arcturus, then spike (or speed on) to Spica". Together with the bright stars Spica and Denebola (or Regulus, depending on the source), Arcturus is part of the Spring Triangle asterism. With Cor Caroli, these four stars form the Great Diamond asterism. Ptolemy described Arcturus as subrufa ("slightly red"): it has a B-V color index of +1.23, roughly midway between Pollux (B-V +1.00) and Aldebaran (B-V +1.54). η Boötis, or Muphrid, is only 3.3 light-years distant from Arcturus, and would have a visual magnitude −2.5, about as bright as Mercury from Earth, whereas an observer on the former system would find Arcturus as bright as Venus as seen from Earth. In 1984, the 90 cm (36-inch) reflecting Yapp telescope at Herstmonceux was tested with an echelle spectrograph from Queen's University Belfast and a CCD camera. Observations of the stars Arcturus and Deneb (Alpha Cygni) were conducted in the summer of 1984. Physical characteristics Based upon an annual parallax shift of 88.83 milliarcseconds as measured by the Hipparcos satellite, Arcturus is from the Sun. The parallax margin of error is 0.54 milliarcseconds, translating to a distance margin of error of ±. Because of its proximity, Arcturus has a high proper motion, two arcseconds a year, greater than any first magnitude star other than α Centauri. Arcturus is moving rapidly () relative to the Sun, and is now almost at its closest point to the Sun. Closest approach will happen in about 4,000 years, when the star will be a few hundredths of a light-year closer to Earth than it is today. (In antiquity, Arcturus was closer to the centre of the constellation.) Arcturus is thought to be an old-disk star, and appears to be moving with a group of 52 other such stars, known as the Arcturus stream. With an absolute magnitude of −0.30, Arcturus is, together with Vega and Sirius, one of the most luminous stars in the Sun's neighborhood. It is about 110 times brighter than the Sun in visible light wavelengths, but this underestimates its strength as much of the light it gives off is in the