Partial Lunar Eclipse 19 November 2021

WAITING FOR THE SHADOW

Astronomical Observing, Eclipses, and Photography - Joseph Cali

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Partial Eclipse of the Moon - Syzygy at Sunset on November 19^th, 2021

On November 19th, 2021, a partial lunar eclipse occurs in the afternoon and early evening. Half of the eclipse will already be over by the time the Moon rises. In fact maximum eclipse and moon rise are only minutes apart and the remainder of the eclipse occurs during twilight. The eclipse is classed as partial but is very nearly a total eclipse with the Moon grazing the edge of the Earth's umbra much as it did last May where it was classed as a total but one limb remained bright. The eclipse is at greatest eclipse just as the Moon is rising and the sun is setting. The Moon is going to be very difficult if not impossible to see at this time. the atmosphere will dim the already faint Moon and the sky will still be bright.

There are three officially named and defined twilights, Civil, Nautical and Astronomical Twilight. An understanding of these will help understand the observation limits.

The brightness of the sky obviously varies during each twilight and varies depending what part of the sky you are looking at so the following descriptions of sun altitude are accurate but the appearance descriptions are necessarily approximate.

Civil twilight is when the Sun is between 0^o and 6^o below the horizon. The sky is a fairly light blue. It is still easy to see the landscape.
Nautical twilight is when the Sun is between 6^o and 12^o below the horizon. The sky becomes dark or deep blue. The landscape becomes more difficult to see.
Astronomical twilight is the period when the Sun is between 12^o and 18^o below the horizon. The sky becomes quite dark to the human eye and the ground difficult to see in the absense of artificial lighting but long exposure astrophotography will pick up the sky glow.
Long exposure full spectrum astrophotography can begin at the end of evening astronomical twilight and continue in the absense of the Moon and artificial light pollution until the beginning of morning astronomical twilight.

So as time passes and the Moon rises, the twilight sky is continually dimming and at some point, the sunlit crescent of the Moon will become visible and at a later time, the eclipsed (red) part of the Moon may become visible against a darker blue sky. The Moon may be visible right from moonrise. If you saw the lunar eclipse around sunrise on July 28, 2018, this event will be somewhat similar. In the photo below, the faint outline of the totally eclipsed Moon is visible setting on the western horizon during the July 2018 eclipse.

I can't say for sure whether or not it will be visible at moonrise due the the sky brightness. Even if it's possible to see it as the Moon rises, if you don't know exactly where to look, you probably won't see it even if it's visible at moonrise.

The Moon rises at an azimuth of 66^o east of north at 19^h46^m eastern daylight time in Canberra. On a magnetic compass, the deviation in and around the ACT varies from 12^o - 12.5^o depending where you are observing from around the ACT/NSW border zones. So 66^o east of north corresponds to a bearing of about 78.5^o magnetic east.

Lunar Eclipse Contacts , Sunset, and twilight times

Eclipse Event	Contact Label / Description	Time [EDT]
Penumbral Begins	P1	17:02:09.0
Partial Begins	U1	18:18:42.7
Sunset / Moon rise	Bright sky	19:50
Greatest Eclipse	GREATEST	20:02:55.5
Civil Twilight	Light Blue Sky	20:20
Nautical Twilight	Dark Blue Sky	20:54
Astronomical Twilight	Dark Sky	21:32
Partial Ends	U4	21:47:06.9
Penumbral Ends	P4	23:03:43.8

This photo above shows the faint dim red disc of the totally eclipsed setting Moon taken about 20 mins before sunrise and during civil twilight. It gives some indication of how difficult it may be to see the rising eclipsed Moon. On Nov 19, the Moon will have a brighter sunlit white cusp. As the twilight sky darkens and the sunlit crescent grows, the Moon should fairly quickly become easier to identify. In the table below I have listed in chronological order, the various lunar eclipse phases as well as sunset and moonrise and the twilight times.

No doubt, the click baiters will be out in force with pictures of giant bright red Moons, artificaially perched on various skylines. Don't be fooled, this won't be easy to see but that's the fun of the observing challenge. As the eclipse progresses it will quickly become more visible.

In the illustration below, I have attempted to depict the lunar visibility against background sky brightness and colour graphically with estimated brightness of sky background. This is not easy to predict or illustrate even though I have observed many sunrise/sunset lunar eclipses. The entire event takes place bewteen rise ENE, and end of eclipse NE so make sure you have a good view to the north east!

Good luck and clear skies!

Joe