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QUESTION: Hi,

Unfortunately a fellow expert, Patrick Weiler, could not help, maybe you can, please.

We are told Merak is 79 ly away from earth and Phekda is 84 ly away. But how far from Merak is Phekda ? Each measurement of the star in question is measured from earth, and 'though to us on earth all stars are brighter or dimmer to our eyes, we do not see the third dimension of how far apart from each other are they. Ideally I would love to know how far apart each of the stars of the Plough are from each other. I am hoping to do a three dimensional scale model of the Plough, and of course the Pole star, but without this information, approximate as it might be, I cannot proceed. So, the real question is : how far from Alpha is Beta, how far from Beta is Gamma, How far from Gamma is Delta, how far from Delta is Epsilon, how far from Epsilon is Zeta, how far from Zeta is Eta. Now, it would help too if I knew how far Alpha is from Delta, and how far Eta is from Delta as this would give me approximate angles for my construction. To add finally, if the above information can be found, how far from Mizar is the "rider" Alcor. And, as I forgot, sorry, how far from Dubhe (Alpha) is the Pole star ?

Many thanks, with real appreciation,

Aidan.

ANSWER: In order of distance from Earth:

Megrez 58 light years

Mizar 78 light years

Merak 79 light years

Alioth 81 light years

Phecda 84 light years

Alkaid 101 light years

Dubhe 124 light years

The distance between Alcor and Mizar is estimated to be 74,000 AU's (+/- 39,000 AU's) and the Pole Star is 434 light years from Earth.

Hopefully this will enable you to determine how far from each other each star is.

---------- FOLLOW-UP ----------

QUESTION: Thank you for the information on Alcor/Mizar, and the approximate distance the earth is from the Pole star. This information is quite helpful thank you, But............. How far apart are the stars within the Plough from each other ??? Megrez being 58 ly is interesting, but I have read that while it is 58 ly from the solar system, it is also 78 ly from earth, so I am confused about that. But to the main quest, how far apart from each other are the Alpha through Eta stars ? Many thanks for your almost immediate response. Aidan

Because all the measurements of the distances of the stars are from earth, you simply take one from the other (so that means that Megrez is 20 light years from Mizar, but Merak is only one light year away from Mizar). Unfortunately, I do not have access to the information about the Alpha to Eta stars though.

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Comment | Very quick response thank you all. Unfortunately nobody can tell me how to measure the stars latterly, that is from star to star left to right or right to left or whatever as in how far Dubhe is from Megrez etc. But thanks for trying. |

Astronomy

Particular expert in eclipses (both solar and lunar), but able to answer most questions about astronomy or refer to a website that can help

Have been interested in eclipses since August 1999 and hope to see the annular eclipse in Scotland next year