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Using the Big Dipper as a Stargazing Signpost

Part of the Stargazing For Dummies Cheat Sheet (UK Edition)

One of the great signposts in the northern hemisphere sky is the Big Dipper, also known as the Plough, an asterism in the constellation of Ursa Major. If you can find the Big Dipper, then you’re well on your way to finding lots of other constellations.

‘Dipper’ is an American word for a large ladle for scooping liquid. The Big Dipper asterism has three stars in a curve representing the handle, and four stars at the end of the handle representing the scoop.

  • Pointers to Ursa Minor: The two brightest stars in Ursa Major, α Ursa Majoris and β Ursa Majoris, lie at one end of the Big Dipper asterism. If you picture this dipper lying down, with the base of the scoop on the ‘floor’, draw a line up from β Ursa Majoris through α Ursa Majoris and keep going until you get to the next bright star, which is Polaris, α Ursa Minoris, the North Star. Polaris lies at the end of the tail of Ursa Minor and the end of the handle of the Little Dipper asterism. The rest of Ursa Minor curves from the North Star towards the four stars in the scoop of the Big Dipper.

  • Carry on to Cassiopeia: Draw a line from α and β Ursa Majoris through α Ursa Minoris, the North Star, and go the same distance again on the opposite side of Ursa Minor, and you arrive near the distinct zigzag shape of Cassiopeia (which often looks like a W, an M or an E shape, depending on which position the constellation is in when you’re observing it).

  • Little Dipper pointers to Draco: After you find the North Star using the pointers of the Big Dipper, and once you’ve found the asterism of Ursa Minor, then lying between the Big and Little Dippers is the curve of stars making up part of the constellation Draco. Locate the head of Draco using the four stars that make up the scoop of the Little Dipper. Imagine the Little Dipper lying down, with the base of the scoop on the ‘floor’, with its handle rising up and to the left. The head of Draco sits ‘below’ the scoop.

  • Arc to Arcturus: Go to Ursa Major, to the handle of the Big Dipper. The three stars in this handle form an arc, and if you continue this arc, it will lead you to the bright orange star Arcturus, α Boötis. This pointer is easy to remember: just arc to Arcturus.

  • Spike to Spica: After you arc to Arcturus, continue in that direction in a straight line, driving a spike down to the next bright star, Spica, α Virginis. So remember arc to Arcturus and then drive a spike to Spica.

  • Little Dipper arcs to Camelopardalis: Another signpost in this part of the sky uses the tail of Ursa Minor, the handle of the Little Dipper, to arc to Camelopardalis. It’s not nearly as catchy as arcing to Arcturus, but Camelopardalis is a very faint constellation that’s hard to find, so having a signpost is very handy.

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