Posts Tagged ‘Twilight’

05/07/2018 – Ephemeris – Twilight

May 7, 2018 Comments off

Note:  Sorry for the delay.  I was hit with a fast developing cold Sunday.  So I was unable to post this at my normal time, and was unable to record my next Tuesday through Monday programs.

Ephemeris for Monday, May 7th. The Sun rises at 6:24. It’ll be up for 14 hours and 30 minutes, setting at 8:55. The Moon, at last quarter today, will rise at 3:14 tomorrow morning.

We are in the time of year when it appears that twilight doesn’t seem to end. There are three definitions of twilight, Civil, Nautical and Astronomical. Each ends in the evening when the Sun is 6, 12, and 18 degrees below the horizon respectively. Astronomers don’t really care about civil twilight, the sky is too bright. Sailors using a sextant for star positions can usually see the horizon for star sighting up to the end of nautical twilight. Astronomers consider the skies dark at the end of astronomical twilight, barring he Moon being up. The brightest stars and planets become visible a half hour after sunset. We begin to pick out constellations at the end of nautical twilight. For instance, for tonight, nautical twilight ends at 10:10 p.m., while astronomical twilight ends at 10:57.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Categories: Concepts, Ephemeris Program Tags:

06/27/2016 – Ephemeris – Astronomical twilight lasts till after midnight… Bummer!

June 27, 2016 Comments off

Ephemeris for Monday, June 27th.  Today the Sun will be up for 15 hours and 33 minutes, setting at 9:32, and it will rise tomorrow at 5:59.  The Moon, at last quarter today, will rise at 1:57 tomorrow morning.

Here we are a week into summer and we find that the latest sunset was already last night.  That means that the last vestiges of twilight* don’t end until just after midnight.  It wouldn’t be so bad if the Sun was in the south at noon instead of 1:43 in the afternoon, due to being in the extreme western part of the eastern time zone and the imposition of daylight time.  For latitudes north of 48 ½ degrees, twilight currently doesn’t end.  That latitude will move northward as the Sun heads south.  As it is now we in the Grand Traverse region are currently getting only 4 ½ hours of darkness Moon willing.  And it won’t for the next few days at least.  Our darkness situation will start to get better in about a month from now.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

*Astronomical twilight begins and ends when the Sun is 18° below the horizon.

05/19/2016 – Ephemeris – Daylight Saving Time in West Michigan

May 19, 2016 Comments off

Ephemeris for Thursday, May 19th.  Today the Sun will be up for 14 hours and 59 minutes, setting at 9:09.   The Moon, 2 days before full, will set at 5:49 tomorrow morning.  Tomorrow the Sun will rise at 6:08.

It is nearing summer and the powers that be have bequeathed on us daylight saving time, even starting it before the end of winter since 2007.  It is a thing that amateur astronomers hate.  This time of year through the end of July the Sun just sets too late, and if one has a day job, it’s nearly impossible to stay up long enough to start observing at 11 p.m. or midnight, and be bright-eyed and bushy-tailed the next morning.  Nautical twilight, when the sea horizon is no longer discernible ends at 10:28 p.m. tonight, and astronomical twilight, when it’s pitch dark, ends at 11:19.  It gets worse the farther north and west you go in the Eastern time zone.   At least this year we have three planets to entertain us in the evening twilight.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.


Time Zone Map

Our place in the Eastern Time Zone. Source  If you are using Firefox right-click on the map and select View Image to enlarge.

We are near longitude W 86°.  Our Eastern Standard time meridian is W 75°, which runs through Philadelphia, which I’ve added to the map, southwest of New York.  With 15° per hour that makes that 44 minutes behind Philadelphia.  Theoretically time zones should extend 30 minutes on either side of a standard time meridian.

During daylight time our time meridian is W 60°, which is off the map.  That meridian just ticks the eastern end of Nova Scotia in Canada.  For us near 45° north latitude astronomical twilight ends shortly after midnight.

08/29/2014 – Ephemeris – Twilight is shorter now than it was in June

August 28, 2014 2 comments

Ephemeris for Friday, August 29th.  The sun will rise at 7:01.  It’ll be up for 13 hours and 22 minutes, setting at 8:24.   The moon, half way from new to first quarter, will set at 10:09 this evening.

Here we are at the end of August already.  We have one more night to view the Milky Way in darkness after the moon sets, because the Moon sets at the very end of astronomical twilight.  By the way, astronomical twilight starts and ends when the sun is 18 degrees below the horizon, and the actual twilight glow is completely gone.  The sun sets more than an hour before it did in late June, which means that it gets dark much earlier.  Twilight lasted much longer in June than it does now because the Earth’s rotation now drops the sun below the horizon at a steeper angle.   As a matter of fact while the sun sets an hour earlier now than in June, twilight ends two hours earlier.  It sneaks up on you if you’re not paying attention to it.

Times are for the Traverse City/Interlochen area of Michigan.  They may be different for your location.


Tonight's end of astronomical twilight

Distance the Sun must travel from the horizon to 18 degrees below tonight, August 29, 2014. Created using Stellarium.

 Solstice end of twilight

Distance the Sun must travel from the horizon to 18 degrees below, the night after the June solstice, June 22, 2014. Created using Stellarium.

Categories: Ephemeris Program, Twilight Tags: