Polaris

Polaris (α Ursae Minoris, α UMi, commonly the North Star or Pole Star) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star.

It is a multiple star, comprising the main star, α UMi Aa, which is a supergiant; two smaller companions, α UMi B and α UMi Ab; and two distant components, α UMi C and α UMi D. α UMi B was discovered in 1780 by William Herschel.

The revised Hipparcos parallax calculates the distance to Polaris at about 434 light-years (133 parsecs). Many recent papers derive distances up to 30% closer, particularly by assuming that its pulsation is in the fundamental mode. Deriving an accurate distance is especially important because Polaris is the closest Cepheid variable to Earth, so its physical parameters are critically important to the whole astronomical distance scale.

History of observations

Polaris in stellar catalogues and atlases

Star system

α UMi Aa is a 4.5 solar mass (M_☉) F7 yellow supergiant (Ib). This is the first classical Cepheid to have a dynamical mass determined from its orbit. The two smaller companions are α UMi B, a 1.39 M_☉ F3 main-sequence star orbiting at a distance of 2400 AU, and α UMi Ab (or P), a very close F6 main- sequence star with an 18.8 AU radius orbit and 1.26 M_☉. There are also two distant components: α UMi C and α UMi D which have been shown to not be physically associated with the other three stars.

Polaris (convention)

Polaris (formerly Toronto Trek) is an annual science fiction and fantasy convention held in Toronto, Ontario, Canada in the past and now held in Richmond Hill, Ontario, Canada.

It began in 1986 as a relaxacon as Toronto Trek Celebration. Two years later, in 1988, Toronto Trek Celebration 2 took place. In 1989 it dropped the word "Celebration" and became simply "Toronto Trek". For its twenty-first convention in 2007, the name was changed to "Polaris". At Polaris 26, held July 5–7, 2012, it was announced Polaris had come to an end and that a new convention would replace Polaris in 2013.

The convention had a focus on media guests from science fiction, fantasy movies and television series and novel authors such as Star Trek, Babylon 5, Stargate, Doctor Who, Buffy the Vampire Slayer, Jericho, Lost and Battlestar Galactica. Photo opportunities, autographs and Question & Answer sessions feature the media guest, who sometimes come to other programming and after hours events.

USS Periwinkle (1864)

USS Periwinkle (1864) was a steamer procured by the Union Navy during the final months of the American Civil War. She served the Union Navy’s struggle against the Confederate States of America as a patrol gunship.

After the war, this ship was retained by the U.S. Navy to support the Hall Scientific Expedition to the Arctic Ocean, and during this voyage – under her new name Polaris – she proceeded into Arctic waters, only to have her hull crushed by the ice.

Construction

America, a heavy screw tugboat built at Philadelphia, Pennsylvania, in 1864, was purchased by the Union Navy 9 December 1864 from John W. Lynn; renamed Periwinkle; and commissioned early in January 1865, Acting Master Henry C. Macy in command.

Assigned to river patrol in the Potomac River

The two-masted, schooner-rigged, white oak tug joined the Potomac Flotilla 15 January 1865 as a gunboat, and operated primarily in the Rappahannock River.

In mid-March, a fleet of oyster schooners operating in the area was threatened by a Confederate enemy force, and Periwinkle with USS Morse, blockaded the mouths of the Rappahannock and Piankatank rivers to protect them. The Flotilla also interrupted contraband business between lower Maryland and Virginia, and cleared the rivers of mines, and fought guerillas ashore.

Aurora

An aurora, sometimes referred to as a polar light, is a natural light display in the sky, predominantly seen in the high latitude (Arctic and Antarctic) regions. Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere), where their energy is lost. The resulting ionization and excitation of atmospheric constituents emits light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes. Different aspects of an aurora are elaborated in various sections below.