New Moon & Night When moon does not rise - Difference?

[Pingster]

Maybe a pro can help me out here. Being a DSO fan i like to observe when theres no moon.

Looking at a moon calendar. I have noticed theres 1 day of new moon a month, but there can be many days when theres a partual moon, yet the moon either never rises, or sets early in the evening at 8pm. Or it rises late in the morning at sat 6am.

So my question is, is it still darker at new moon than when the moon is partual, yet is not in the night sky at all during our observation session :/

[JimStan]

I would suspect that the question would be mostly academic, since almost every civilized corner of the earth is beset with Urban light pollution. Maybe back in the years before electric lighting became so pervasive, there might have been a difference. I think of how Messier was able to see his famous "M objects" with a scope of less than 50 mm effective aperture ! ( equivalent to a set of nightime binoculars ).

See this Wiki article on the topic of "Astronomical Twilight", which might help to answer your question.

Twilight - Wikipedia, the free encyclopedia

Frankly, here in Western Maryland, USA, there is so much light pollution due to Urban sprawl, that we hardly ever see skies darker than "Astronomical Twilight" anyway. It's a darn shame. At one time, the Milky Way could be seen brightly arching across the Summer sky from the center of our town. Now one has to drive miles out into the countryside to see it at all, and the views from about 30 degrees, down to the horizon, are fairly well lit up by light domes from towns scattered in all directions!

[acey]

So my question is, is it still darker at new moon than when the moon is partual, yet is not in the night sky at all during our observation session :/

The sky is dark as long as the moon is below the horizon, even if it's a partly illuminated moon. Time your observing sessions so that you'll be able to view before moonrise or after moonset, whatever the phase.

In theory you would get a certain amount of refracted light from the moon when it's below horizon (analogous to twilight from the sun) but in practice this would only be observable at an ideally dark site with zero light pollution.

As well as timing sessions to avoid moonlight, you also want to maximise observing time when there is no refracted light from the sun. This is the period given by "astronomical twilight" times.

It can still be possible to do useful observing with a low, partially illuminated moon, so it can certainly be worth beginning a session before moonset.

All the above, of course, refers to dark-site conditions. At a light-polluted site the moon makes little difference - it's just another streetlight.

[JimStan]

For our club's "star parties", we try to schedule the events somewhere between "waxing crescent" and 1st quarter. The public LOVES to view the moon, and yet, during that phase of the lunation, it sets soon enough in the evening that a lot of "faint fuzzies" can also be pointed out to the guests.

As mentioned in my earler post regarding light pollution, getting away from man-made light domes is a bigger problem than observing with a partial moon in the sky. It does get a bit dicey between 1st and last quarters, especially around full, because the brightness increases many-fold during those phases.

Jim S.

[m.tweedy]

try this moonrise and moonset calendar

Moonrise, Moonset and Moonphase for United Kingdom – England – London – coming days

you can use this to calculate when to observe before the moon rises

[Pingster]

Great replies, will be very useful to many newbies like myself. Thank you. And as JimStan said, says where theres a part moon that sets early is a bonus for moon observing