Event Date: June 12th
Time: 4:35(.47) AM
Brief
As mentioned at the end of yesterday's detailed section, I previewed for today's entry a bit, as a continuation. Now as seen below, we see the sky more blue than black in the image; sounds like an injury update, I know! Getting back to astronomy, the time shows the start of nautical twilight. Since the Sun rises only two seconds earlier and moves less than 4 arc-minutes further north, the beginning of nautical twilight is about the same as it would be yesterday if I did two journals on the same day. I kept the same deep sky objects labeled as yesterday, while some others are just beginning--or about--to clear the horizon. We will see lots of these much more clearly as they become further separated from the Sun during the summer, while they rise in the evening during the fall.
Time: 4:35(.47) AM
Brief
As mentioned at the end of yesterday's detailed section, I previewed for today's entry a bit, as a continuation. Now as seen below, we see the sky more blue than black in the image; sounds like an injury update, I know! Getting back to astronomy, the time shows the start of nautical twilight. Since the Sun rises only two seconds earlier and moves less than 4 arc-minutes further north, the beginning of nautical twilight is about the same as it would be yesterday if I did two journals on the same day. I kept the same deep sky objects labeled as yesterday, while some others are just beginning--or about--to clear the horizon. We will see lots of these much more clearly as they become further separated from the Sun during the summer, while they rise in the evening during the fall.
 | |
|
The start of nautical twilight happens 44 minutes later than astronomical. This makes sense...if you remember my numerous showings of the celestial graph of course, pointing near the north axis. As the Sun rises further north of east each day, that means that time time below the horizon has it approaching the horizon more and more gradually. As it gets closer to the horizon between nautical and civil twilight starts (12 and 6º respectively) and then civil to Sunrise, the times become shorter. That is why yesterday if you recall, I mentioned an average time of the twilight phase durations, rather than each individually at this time of year. I will remind with the celestial grid tomorrow, and put it in the image as we conclude this 3-part series of starting twilight in the northeast. With the Sun rising close to its most north-of-east azimuth mark and the earliest Sunrise happening at our latitude tomorrow, it will be a fitting time to show that.
No comments:
Post a Comment