(meteorobs) Lyrid lunacy

[Bruce McCurdy]

    Happy International Astronomy Day, everyone! Bob L. wrote:

> During this period the moon reaches its first quarter phase on Tuesday 
> April
> 24. At this time the half illuminated moon will set near 0100 local 
> daylight
> time and will not interfere with observing the remainder of the morning.

    Typically a waxing crescent Moon doesn't interfere much with pre-dawn 
meteor observing; *on average*, a first quarter Moon sets at local midnight 
(0100 LDT), and anything younger than that might be expected to set 
commensurately earlier. Not so at this time of year, and esp. at this stage 
of the 18.6-year cycle of the nodes.

    On April 22 in Edmonton (~ 53.5° N., 113.5° W.) the Moon will be less 
than five days old and just 30% illuminated as it sets at the ridiculous 
hour of 03:14 MDT! That's ~100 minutes *after* local midnight.  A five-day 
old Moon will always be high at Lyrid time as it's fairly near 6h R.A., at 
the top of the ecliptic in Taurus-Gemini. This one is particularly so 
because the maximum of the cycle of the nodes -- a.k.a. the Lunar 
Standstill -- was reached just last year. Tomorrow the Moon will be at  > 
+27° declination, close to the maximum possible.

    The good news for observers is that the Moon will be almost 180° in 
azimuth removed from the radiant, and of course it won't be nearly as bright 
as a Moon that is typically setting at such an hour.

> The [Lyrid] radiant would reach
> thirty degrees elevation earlier for locations further north and later for
> locations further south. The best time to view this activity is just 
> before the start of morning twilight, when the radiant lies highest in a 
> dark sky.

    Even in a "normal" year the advantage we northerners enjoy from the 
earlier rising of the radiant is more than offset by the earlier onset of 
morning twilight. This year that is further exacerbated by the (much) later 
setting of the Moon at more northerly latitudes.

    Just for fun I did Guide simulations for a few chosen latitudes along 
the Mountain (Daylight) Time meridian of 105° W.

Lat.    radiant =30°     moonset       morning twilight
-------------------------------------------------------
30°     ~ 00:15              00:41            05:02
38°     ~ 00:00              01:11            04:40
46°     ~ 23:45              01:48            04:08
54°     ~ 23:30              02:43            03:14
62°     ~ 23:10          circumpolar     perpetual
-------------------------------------------------------

    So the window to observe meteors in a truly dark sky -- between moonset 
and twilight -- narrows rapidly as our virtual observer heads north. 
Especially this far north.

    Alas, virtual observing is all I will likely be doing as we have been 
socked in under a 300m ceiling for days. Prospects of clearing are non-zero, 
but I'm not confident. I guess I can console myself that I'd only be missing 
a half-hour window of true darkness on Sunday morning, and none at all on 
Monday.

    Bruce
    *****