A star has been found that may be a sister of our Sun, born in the same cloud of gas and dust in our galaxy, the Milky Way. The Sun, the Earth and the other planets coalesced some 4.54 billion years ago within a such a cloud, probably with thousands of other stars. This age comes from radiometric measures of radioactive isotopes and their decay products in meteorites, the oldest rocks we can handle, while there is plenty of observational evidence for ongoing star formation elsewhere in the galaxy.
Only last week, news emerged of more than 300 previously-unrecognised clusters of young stars, still largely obscured by dust. In time, and usually within a few hundred million years, such stars emerge from their dusty cocoons and drift apart to follow their own orbits about the centre of the galaxy. Being built from the same raw material gives each of the stars precisely the same chemical makeup, while their orbits too can point to a shared origin.
These clues have been used by a team of astronomers led by the University of Texas to identify the Sun's potential sibling. Still unnamed but known as HD 162826 or by a number of other catalogue designations, it is plainly visible through binoculars high in our summer night sky. Our chart depicts a band of sky more than 50° wide and centred some 70° high in our SSE at midnight at present. Vega in Lyra is by far the most obvious star, though the equally-bright Arcturus in Bootes stands another 15° beyond the chart's right-hand border.
HD 162826, truncated to HD on our chart, lies 110 light years away in NE Hercules 9° to the W (right) of Vega and at the W end of a curving row of three stars. These are shown in the circle which is a magnified view of an area slightly larger than the Moon – star 90 is 90 Herculis which shines at magnitude 5.2, while HD is 6.5 and the star between them is 6.0. HD is 15% more massive than the Sun but whether it, too, hosts planets and life remains to be seen.
Very much more distant in Hercules are the globular star clusters M92 and, even more spectacular, M13. Appearing as fuzzy balls of light of mag 6.3 and 5.8, they lie about 16,000 and 25,000 light years away respectively and contain hundreds of thousands of ancient stars.
Further W lies Corona Borealis, the Northern Crown, and two very different variable stars. R usually shines near mag 6, the limit of naked-eye visibility. Since 2007, though, it has been some 1,500 times fainter near mag 14 because of soot forming in its atmosphere. T, a recurrent nova, is currently a dim 10th mag telescopic object has been known to flare to mag 2 – the last time in 1946.
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