Use a diagram to explain what is meant by the parallax angle, p, for a star observed twice from Earth, with a 6-month interval between each observation. Hence define the parsec, and calculate its value in astronomical units and metres. The star Betelgeuse is observed to have a parallax angle p = 4.5 × 10−3 arcseconds. State the distance of Betelgeuse in units of parsecs and light years.

Use a diagram to explain what is meant by the parallax angle, p, for a star observed twice from Earth, with a 6-month interval between each observation. Hence define the parsec, and calculate its value in astronomical units and metres. The star Betelgeuse is observed to have a parallax angle p = 4.5 × 10−3 arcseconds. State the distance of Betelgeuse in units of parsecs and light years.