Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Venus in daylight in southern latitudes
    From: Frank Reed
    Date: 2021 Oct 21, 20:21 -0700

    The phase of Venus this week, as seen through a backyard telescope is approximately half full. You won't see that through a sextant scope (or in any wide-angle photo) since the angular diameter of Venus is only about 0.4 minutes of arc. Jupiter right now is twice that size, and that's only barely recognizable as a disk in a sextant with a high-power scope. As Venus approaches inferior conjunction, passing within a few degrees of the Sun in the sky, its angular diameter will increase but the crescent will become thinner. This is part of the reason that we reach a point of maximum brightness in early December. 

    On the last day of December Venus will be a thin crescent just 13° from the Sun. By then Venus will have an angular diameter slightly greater than 1.0 minute of arc. Though on that date, Venus is really too close to the Sun to use for navigation, it would be possible two weeks earlier when the elongation is near 30°. There's a debatable question here for sextant sights. If your magnification is too low to resolve the disk of the planet, then should you use the "center of light" for Venus? This is basically the limb of that thin crescent which is about 0.5 minutes from the center of the disk. But then again, if your magnification is so low, does half a minute of arc make a difference in the first place? And if your scope's magnification is higher, you should be able to make out the little crescent visually, and then you can easily shoot the center of the disk, as is normal.

    Frank Reed

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site