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Forum Replies Created

Viewing 15 posts - 1 through 15 (of 580 total)
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  • in reply to: JULY – Historical Astronomy Dates #16339

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    Ah, but Galileo told people about it 😉

    in reply to: Detailed Images of Mars #16181

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    xkcd.com

    in reply to: Asteroid near miss! #16083

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    just one Lunar distance away

    Away from us and not from the Moon, I hope!

    in reply to: Asteroid near miss! #16077

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    That’s some peanut!

    in reply to: Jupiter and Moon conjunction and my week of stargazing #16034

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    Focus the telescope by eating the doughnuts

    Tej, you should write an astronomy travelogue book with that as the title!

    in reply to: M13 Hercules Cluster from ahem…my Living room window #15983

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    Wow! Amazing, Tej!!

    in reply to: Star Gazing Live #15937

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    Didn’t see it at all, but TBH I haven’t rushed to watch it on iPlayer. I always feel a bit as though Dara O’Briain is trying to be Brian Cox and Brian Cox is trying to be Dara O’Briain. And only one of them is coming close to succeeding.

    in reply to: Clear Skies!…So whats on sky? #15784

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    The astrophotography video we show at the beginning of our lectures. You can send it to Flamsteed@rmg.co.uk – file size shouldn’t be a problem. Thanks!

    in reply to: Clear Skies!…So whats on sky? #15781

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    here is the result.

    Cool! Care to send a copy to me for the video?

    in reply to: MARCH – Historical Astronomy Dates #15703

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    Frederick William Herschel discovered a new planet, Uranus

    Thereby doubling the size of the solar system, from 9.5AU to 19AU. Not a bad day’s work!

    in reply to: National Geographic's top places for dark skies #15468

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    You got image 3 and 2 out of image 1??? Wow!!!

    Rupert, could I ask you to send those to me please and I’ll figure out a way of incorporating them into the video in an effective way? Thanks! Wow.

    in reply to: Johannes Kepler – Almost Isaac Newton #15445

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    Well, there’s a coincidence!! Two of the contestants on tonight’s Mastermind had as their specialist subjects (i) Johannes Kepler and (ii) Isaac Newton!!

    in reply to: ISS seen from Galloway #15415

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    Thanks for that, Mike. I eventually remembered that there’s a ‘show satellites’ option on Stellarium, too, though the dataset on the mobile app seems more complete than the desktop app which doesn’t seem to have this particular piece of space hardware.

    in reply to: Holographic Principle #15029

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    *brain hurts*

    in reply to: Johannes Kepler – Almost Isaac Newton #14999

    Andy Sawers
    Moderator
    Topics: 113
    Replies: 588

    how did Kepler know Mars orbital period in the first place

    A bit of brilliance on Copernicus’s part, I believe.

    Imagine that a planet is at opposition – so it culminates/appears due south at midnight. Then wait for the next time it’s at opposition. Suppose that’s 456 days (1.25 years) later. So in the time it has taken the Earth to travel one-and-a-quarter orbits, the other planet has done only a quarter of an orbit (you know it’s a quarter of an orbit because Earth and the other planet are in alignment with the Sun again). Earth has caught up with and aligned with that other planet.

    So if a quarter of that other planet’s orbital period is 1.25 years, then its actual orbital period is 5 years.

    Here’s the figures for Mars:

    • It takes 780 days for Mars to go from one opposition to the next – its synodic period. That’s 2.137 years, or 2.137 orbits by the Earth around the Sun.
    • In that time, Mars will have gone around 1.137 times (the .137 has to match so that the two planets are aligned at opposition again).
    • 2.137 divided by 1.137 is 1.879. So Mars’s orbital period is 1.879 times as long as the Earth’s. Multiply that by 365 is 687 days – Mars’s orbital period!

    Now go back to that figure 1.82, the ratio of Mars’s orbital period (T) to the Earth’s. Square that number and take the cube root to get 1.52 – Mars’s orbital radius (R) in AU!

     

Viewing 15 posts - 1 through 15 (of 580 total)