- In 2007, Mira was photographed by the Galaxy Evolution Explorer (GALEX) spaceborne observatory, in the ultraviolet light. These photos revealed, as a big surprise, that Mira possesses a comet-like tail of about 13 light-years length. This tail is probably composed of material that was once ejected by Mira, over the past 30,000 years. While it is not immediately certain, the formation of a tail may have to do with Mira’s comparatively high velocity with respect to the surrounding stars and part of the Milky Way galaxy: Mira moves at about 130 km/s.
- Mira is about 350 light-years from Earth.
- Hold out your right hand at arm’s length with thumb and little finger outstretched. Put your thumb on Jupiter in the evening sky and tilt your hand clockwise a little; your little finger will be near Mira.
- For about five months Mira is invisible, then in the next six months it gradually increases in brilliance, until finally it shines with the beautiful sparkle of a star of the second magnitude. This peak of brilliance lasts for about a fortnight, after which time it again starts slowly to fade. At various times it has not been seen at all with the naked eye for several years consecutively, — and its maxima and minima are even more irregular.
- Each pulse lasts a decade or more, and an amount of time on the order of 10,000 years passes between each pulse. With every pulse cycle Mira increases in luminosity and the pulses grow stronger. This is also causing dynamic instability in Mira, resulting in dramatic changes in luminosity and size over shorter, irregular time periods.
- From northern temperate latitudes, Mira is generally not visible between late March and June due to its proximity to the Sun. This means that at times several years can pass without it appearing as a naked-eye object.
- Mira is the only known star with a comet-like tail. It is also enveloped by a puzzling spiral structure.
- Mira is also the dominant component of a double star, which is separated by only 0.6 arc seconds. As the companion orbits Mira in about 400 years, it has now just once orbited the star since Fabricius discovered its variability. The linear distance was given as about 70 Astronomical Units, i.e. 70 times the distance between Earth and Sun. The companion is probably a white dwarf in interaction with Mira, which is surrounded by an accretion disc of material which it has captured away from the red giant Mira, and which may well be brighter than the companion star itself. This companion has a brightness which also varies, between 9.5 and 12 visual magnitudes (its variable star designation is VZ Ceti). Its variation is rather complicated: A slow variation of about 13 years period is superimposed by rapid fluctuations over minutes, and occasionally a rare flare of some minutes duration.
- The new high-resolution images reveal the close interaction between Mira and its companion. Despite their rather large separation, the two stars have had a strong effect on one another and the new images demonstrate how double stars can influence their environments and leave clues for what will be their future fate.
- The total swing in brightness from absolute maximum to absolute minimum (two events which did not occur on the same cycle) is 1,700 times. Interestingly, since Mira emits the vast majority of its radiation in the infrared, its variability in that band is only about two magnitudes. The shape of its light curve is of an increase over about 100 days, and a return twice as long.
5. 6. 10. http://en.wikipedia.org/wiki/Mira