Results 1 to 27 of 27

Thread: Naked eye Venus crescent

  1. #1
    Join Date
    Apr 2007
    Posts
    4,467

    Naked eye Venus crescent

    I saw this on the Sky and Telescope website:

    Friday, May 15

    A naked-eye Venus challenge! All week, the large, thin crescent shape of Venus is easy to discern with even a very small telescope or good, steadily braced binoculars. But can you resolve its crescent with your unaided eyes? Mere 20/20 vision isn't good enough; success may await the eagle-eyed with 20/15, 20/12, 0r (rare) 20/10 vision. Try during different stages of twilight before the sky is too dark and Venus's glare becomes overwhelming. Look long and carefully and report your results to Sky & Telescope's Bob King, nightsky55@gmail.com, as told in the May issue, page 49.

    You may improve your chances by sighting through a clean, round hole in a stiff piece of paper 1 mm or 2 mm in diameter (try both). This will mask out optical aberrations that are common away from the center of your eye's cornea and lens.
    Has an eagle-eyed observer here been able to see Venus as a crescent with the naked eye? If my vision was better I might try, but my vision is pretty poor, corrected to 20/20 with eyeglasses or contacts.

    Link (scroll down to Friday May 15): https://skyandtelescope.org/observin...ce-may-8-16-2/
    Last edited by Tucson_Tim; 2020-May-14 at 04:19 AM.

  2. #2
    Join Date
    Jul 2005
    Location
    Massachusetts, USA
    Posts
    22,077
    It shouldn't be possible. The maximum angular size of Venus is about 1.1 minutes of arc, and it is impossible for the human eye to resolve better than 3 or 4 minutes.
    Forming opinions as we speak

  3. #3
    Join Date
    Apr 2007
    Posts
    4,467
    From wiki (https://en.wikipedia.org/wiki/Phases...observations):

    Naked eye observations
    The extreme crescent phase of Venus can be seen without a telescope by those with exceptionally acute eyesight, at the limit of human perception. The angular resolution of the naked eye is about 1 minute of arc. The apparent disk of Venus' extreme crescent measures between 60.2 and 66 seconds of arc,[7] depending on the distance from Earth.

    Mesopotamian priest-astronomers described Ishtar (Venus) in cuneiform text as having horns which has been interpreted as indicating observation of a crescent. However, other Mesopotamian deities were depicted with horns, so the phrase could have been simply a symbol of divinity.[1]
    From astonomy.com:

    Naked-eye sightings of the crescent have long been disputed, with opinions strong on both sides. Chaldean sightings date to 3000 b.c. Some naysayers, however, tout the golden rule that the eyes’ angular resolution is 1' (60") — roughly the apparent size of Venus when largest, making sightings of a crescent impossible.

    But rules are made to be broken, especially given that Dawes’ limit (a formula that gives the resolution of optics) does not apply to planetary observing or daytime/twilight observing, when the resolving power of our eyes’ cone cells are still employed. It applies only to stars of similar magnitude and color seen against a dark sky. Besides, not everyone’s visual acuity is the same, so it’s hard to judge what your results will be.

  4. #4
    Join Date
    Nov 2001
    Posts
    174
    My vision is way worse than 20/20 and Venus does not look like a star to me. My vision problems include astigmatism.

    When I look at the moon, especially a crescent moon, I see several ghost moons stacked side by side as well as a tail on the bottom. When I look at stars, I see them kind of like asterisks with lots more points. So now when I look at Venus I do not see the asterisk like with stars, instead I see a blurry doubled up kind of image with a little tail.

    So I can't see a crescent Venus but it doesn't look like a star either.

  5. #5
    Join Date
    Jul 2005
    Posts
    19,264
    Foveal cones are clustered tightly enough to give a resolution of about half a minute of arc, if the optics are good enough. So at best we'd be looking at a "crescent" rendered in four pixels. Enough to discern that the image of Venus wasn't a disc, and maybe get a sense of its approximate orientation, but no more than that.

    Grant Hutchison

  6. #6
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    9,016
    I can read the 20/20 chart with my rebuilt eyes and glasses, but I cannot come close to resolving Venus.

  7. #7
    Join Date
    Apr 2007
    Posts
    4,467
    Quote Originally Posted by Hornblower View Post
    I can read the 20/20 chart with my rebuilt eyes and glasses, but I cannot come close to resolving Venus.
    The article states:

    Mere 20/20 vision isn't good enough; success may await the eagle-eyed with 20/15, 20/12, 0r (rare) 20/10 vision.

  8. #8
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    9,016
    Too bad that baseball Hall of Famer Ted Williams is no longer with us. During World War II the Navy flight surgeons pegged him at 20/10, and pitchers insisted he could count the stitches on the ball as it came toward him.

  9. #9
    Join Date
    Apr 2007
    Posts
    4,467
    I read in Chuck Yeager's biography that he had 20/10 vision which gave him a distinct advantage -- he could see the enemy fighter planes before they saw him.

    My dad had 20/10 vision -- he could see things I never could. While duck hunting (from a blind on the Mississippi River) he could see the flights of ducks approaching way before I could.
    Last edited by Tucson_Tim; 2020-May-17 at 02:35 AM.

  10. #10
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    15,526
    I tried a couple of nights ago and couldn't really resolve a crescent even with 10x binoculars. I was actually out looking for Mercury, which I still haven't managed to catch.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  11. #11
    Join Date
    Jul 2005
    Posts
    19,264
    20/10 vision sits at the limit of foveal cone density. You can't get any better without redesigning the retinal light receptors. And it only gives you a four-pixel Venus.

    Grant Hutchison

  12. #12
    Join Date
    Apr 2007
    Posts
    4,467
    Quote Originally Posted by Trebuchet View Post
    I tried a couple of nights ago and couldn't really resolve a crescent even with 10x binoculars. I was actually out looking for Mercury, which I still haven't managed to catch.
    10x binocs are hard to hold steady. You will probably need to prop them on something (like the roof of your car) or better yet, a tripod. Good seeing is also a requirement.

  13. #13
    Join Date
    Sep 2004
    Posts
    4,891
    My vision is 20/?? x 1,000 plus without glasses, so if the Moon is a crescent it still looks like a blob in the sky. However, with our cleaned-up telescope.... we will see.
    Do good work. —Virgil Ivan "Gus" Grissom

  14. #14
    Join Date
    Apr 2007
    Posts
    4,467
    For those not familiar with observing Venus thu binocs or telescope, here is an image of the phases from full Venus (close to superior conjunction) to thin crescent Venus (close to inferior conjunction):

    VenusPhases.jpg

    Many, many of these images can be found by doing an internet search for "phases of Venus".

  15. #15
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    15,526
    Quote Originally Posted by Tucson_Tim View Post
    10x binocs are hard to hold steady. You will probably need to prop them on something (like the roof of your car) or better yet, a tripod. Good seeing is also a requirement.
    Yes, good point. I also have trouble getting both eyes to work together.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  16. #16
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    15,526
    I've just been out and seen Mercury! Couldn't quite make it out with the naked eye, but got it with the binocs and little telescope.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  17. #17
    Join Date
    Apr 2007
    Posts
    4,467
    Quote Originally Posted by Trebuchet View Post
    I've just been out and seen Mercury! Couldn't quite make it out with the naked eye, but got it with the binocs and little telescope.
    Congrats! Look again in a few days . . .

    This is from the Sky and Telescope website:

    THURSDAY, MAY 21

    Venus and Mercury are in conjunction in the west-northwest in evening twilight, as shown above. Venus outshines Mercury by 30 times, something the illustration does not convey. Although they look close together, Mercury is on the far side of the Sun from us while Venus is now on the near side. So Mercury this evening is 3.5 times more distant. It's 9.1 light-minutes from us, compared to Venus's distance of 2.6 light-minutes.


    Mercury.jpg

  18. #18
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    15,526
    Cool! I hope it'll be clear, which is no safe bet in these parts.
    Some years back there was a triple conjunction of Venus, Mercury, and Saturn. I was sort of surprised that Saturn was the dimmest of the three, because it was very, very far away.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  19. #19
    Join Date
    Apr 2007
    Posts
    4,467
    The Sky and Telescope website is great. I look at it most every day. Especially the "Sky at a glance" sections: https://skyandtelescope.org/observing/sky-at-a-glance/

    For example, this week's "sky at a glance": https://skyandtelescope.org/observin...e-may-15-23-2/

  20. #20
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    15,526
    Clouds have, of course, descended upon us.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  21. 2020-May-20, 11:55 PM
    Reason
    Not relevant to topic. Just OTB which is not polite.

  22. #21
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    15,526
    I expect there's a good reason why no major observatories are located around here. Although I can see the Dominion Astrophysical Observatory from my house. Weather permitting, of course, which it is not at the moment.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

  23. 2020-May-21, 12:50 AM
    Reason
    Not relative to topic.

  24. #22
    Join Date
    Dec 2006
    Location
    Canberra
    Posts
    2,189
    Venus went retrograde last week so it will now plummet out of sight. Being so close to the June solstice point at the moment, Venus is near the northernmost point of the ecliptic, meaning that in northern latitudes it is high at sunset, while in the Southern Hemisphere it is already low in the sky at dusk. The heliacal setting date in the north is likely to be about 29 May.

  25. #23
    Join Date
    Sep 2004
    Posts
    4,891
    Quote Originally Posted by Trebuchet View Post
    Clouds have, of course, descended upon us.
    Same here, plus rain. No telescope time.
    Do good work. —Virgil Ivan "Gus" Grissom

  26. #24
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    9,016
    Last night I got a glimpse of Venus and Mercury in bright twilight with my Celestron 8. The difference in surface brightness was striking, with Venus being dazzling white and Mercury dull orange. It was during a brief break in a stubborn cloudy pattern over the past week.

    I looked at the sidereal stationary point mentioned by Robert on Stellarium. Venus came close to conjunction with the bright star Elnath (Beta Tauri) about May 12 but did not quite make it. As reckoned relative to the Sun, the star plodded along at constant speed while Venus went faster and faster and started pulling away on that date.

  27. #25
    Join Date
    Jun 2015
    Location
    Houston
    Posts
    1,384
    FWIW I tried looking at Venus crescent last night and the night before with my eyes and could not discern a crescent, but it is still a nice bright object in the sky.

  28. #26
    Join Date
    Nov 2001
    Posts
    174
    Quote Originally Posted by bknight View Post
    FWIW I tried looking at Venus crescent last night and the night before with my eyes and could not discern a crescent, but it is still a nice bright object in the sky.
    Like I said before, I do not see the crescent, but I can tell it is not a star. because, sort of like the way I see the moon, Venus is a blurred dot with a little tail.
    so maybe perfect vision isn't all it's cracked up to be. lol

    although I do miss the seven sisters, i can only see five of them now.

  29. #27
    Join Date
    Jun 2004
    Location
    The Great NorthWet
    Posts
    15,526
    I had great fun last evening watching Venus and Mercury dance in and out of the scattered clouds, despite the inadequacies of a) Meade's finder scope, b) the tripod the telescope is on, and c) my eyeballs. I think I'll try the older tripod tonight.
    Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •