by BDanielMayfield » Sun Feb 01, 2015 5:07 pm
rstevenson wrote:I've been trying to work out (or find out) how far apart the two galaxies are -- their approximate center to center distance. I have figures for their distance from here -- about 290 ly or 89 Mpc -- and for their angular size -- about 2′.3 × 0′.7 for one, and 2′.2 × 0′.8 for the other. But my memory is not stirring when it comes to changing their angular size to ly, and therefore to be able to estimate their distance from each other. (Also, I'm not sure how much of each tail is included in the given angular sizes.) Any number crunchers able to help?
Rob
Since as you point out the tails make us unsure about the lengths of these galaxies I'd use their widths, which are about the same, 0.7' and 0.8' to come up with a scale. But again, where are the endpoints even for the widths to be taken? Just as a guess I estimate the center to center angular distance to be about 1.5' Rob, but this could be way off. Using trig we have Opposite side = Adjacent side x Tanget (adjacent angle) = 290 ly x tan(1.5') = 7.6 ly. Hey, that can't be right. How about 290 million ly which would give 7.6 million light years, plus or minus several million.
Bruce
Edit: shame on me I used 1.5 degrees of arc, it should have been 1.5 minutes: 290,000,000 x tan(1.5/60) = 126,500 light years.
[quote="rstevenson"]I've been trying to work out (or find out) how far apart the two galaxies are -- their approximate center to center distance. I have figures for their distance from here -- about 290 ly or 89 Mpc -- and for their angular size -- about 2′.3 × 0′.7 for one, and 2′.2 × 0′.8 for the other. But my memory is not stirring when it comes to changing their angular size to ly, and therefore to be able to estimate their distance from each other. (Also, I'm not sure how much of each tail is included in the given angular sizes.) Any number crunchers able to help?
Rob[/quote]
Since as you point out the tails make us unsure about the lengths of these galaxies I'd use their widths, which are about the same, 0.7' and 0.8' to come up with a scale. But again, where are the endpoints even for the widths to be taken? Just as a guess I estimate the center to center angular distance to be about 1.5' Rob, but this could be way off. Using trig we have Opposite side = Adjacent side x Tanget (adjacent angle) = 290 ly x tan(1.5') = 7.6 ly. Hey, that can't be right. How about 290 million ly which would give 7.6 million light years, plus or minus several million.
Bruce
[i]Edit: shame on me :facepalm: I used 1.5 degrees of arc, it should have been 1.5 minutes: 290,000,000 x tan(1.5/60) = 126,500 light years.[/i]