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Old 23-08-2019, 12:26 PM
Brown.dog (Tony)
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Newbie question about the moon

Hi Fellow Amateur Astronomers,

Having just bought a Celestron Nexstar 8SE thanks to a nice tax return, I'm about to dip my toes into Amateur Astronomy and thought I better join a forum like this to ask questions and gain knowledge. Thanks to the recent 50th anniversary of Apollo 11 I've watched a lot of docos and movies and I noticed that in all the shots of the moon, Tycho is on the lower hemisphere of the moon rather than the upper hemisphere as we see it. I'm smart enough to deduce that this is because the Americans are photographing it from the northern hemisphere and our orientation is upsidedown (for want of a better word) to them. But my question is, what if you were at the equator, would tycho be sitting somewhere around the equator of the moon? and which direction would it rotate to its new position as you travelled in a straight line from say the north pole to the south pole?


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Old 23-08-2019, 02:13 PM
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Up -v- down, left -v- right etc?

Hi Tony

Welcome to the world of amateur astronomy -- I hope it gives you as much pleasure for many years as it has for me.

Rather than using the term upper and lower, or right and left (as these are all related to which direction you are facing when looking), it is best to use north, south, east and west.

If you look at our moon (naked-eye) not long after it has risen (ie you are facing roughly east), the bottom of the disc is roughly east, the top is west, north is to the left and south the right. This orientation changes as it moves across the sky relative to the observer. By the time the moon is almost ready to set (and you are now facing roughly west), west is at the bottom of the lunar disc, east is at the top, north is at the right and south at the left. Having said that the features on the moon are stationary relative to these directions, as it always keeps one side facing us here on Earth (it is in a tidally locked orbit) which is very common among other planets and their moons too. (Apart from the effects of libration that allows us to see fractionally around the edge to the "far-side" at various points during the month). I'll leave you to go and research what libration is and how it affects which bits of the moon we can and can't see. Search: lunar libration.

So, during the course of the moon crossing our sky here in the southern hemisphere (again naked-eye), not long after the moon rises, Tycho will be on the right-hand side (southern) of the disc. When the observer is facing roughly north and the moon is crossing the imaginary line in the sky that connects north and south here on Earth called the "meridian", Tycho will still be in the south, but is now near the top of the lunar disc as seen from here. When the moon is about to set, it is still (as always) in the south but is now on left-hand side of the lunar disc.

That all should allow you to nut-out where Tycho will be if viewed from the equator or the northern hemisphere during the course of it crossing the sky.

Of course, all this is naked-eye. The view in the eyepiece will differ to naked eye according to the number of refractions and reflections within your telescope. A Schmidt-Cassegrainian like yours, when used with a diagonal has three reflections/refractions and will show a right-side-up view (ie not inverted) but is mirror reversed. Without the diagonal (which is almost always not the case), the image is inverted (upside-down), but not mirror reversed. This inversion and mirror reversal is a normal and natural part of observing with an astronomical telescope and eventually, you will get used to it. It makes no difference once you have worked out which directions are in fact north, south, east and west in the eyepiece -- takes a bit of practice. There is no up, down, left or right, out in space -- these are all man-made arbitrary terms.

As you move the 'scope around while looking through it, it will take some brain-training to comprehend (with many 'scopes -- and the finderscope) that when you move the 'scope "that way" the view seems to move "this way" -- don't worry a bit of persistence and you'll get used to it. All part of the "rights-of passage" into astronomy.


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Old 23-08-2019, 05:07 PM
Brown.dog (Tony)
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Hi L.

Thanks for the explanation, I can see I made a totally wrong assumption. Detailed observation of the next full moon will occur.


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Old 24-08-2019, 11:58 AM
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Allan_L (Allan)
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Hi Tony,
Just a tip.
Most people get more joy (and WOW factor) observing the moon (through a telescope) when it is just half illuminated (quarter moon if you prefer), like tonight, as the sun is at an angle to it and shadows depict the profiles of craters etc more dramatically. IMHO
Trouble is it won't rise until around midnight tonight.
So First Quarter is probably your best viewing time.
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Old 24-08-2019, 12:24 PM
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mental4astro (Alexander)

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Les has offered excellent advise on coming to terms with using an astronomical telescope.

Which is the best phase to view the Moon?

Every phase is!

Sorry Allan, but I will have to challenge you for once!

Tony, have a look through this following thread. It will take you through some of the ins and outs of using your scope with the Moon and planets, plus give you insight into what can be seen not just on the planets, but also the Moon at is different phases. Many people dismiss the full Moon as featureless, but if you know where to look then you will have found the full Moon's hidden treasure!

IIS thread: Observing the Moon and planets - the good juice and cheats

The Moon is also not just about craters. There is so much more. Most people are aware that the darker features are lava fields. What most people then don't consider is if there are lava fields, then there are volcanoes too! The Moon harbours literally hundreds of volcanic domes and long extinct vents, and a myriad of other volcanic features. As there is no air or water for erosion to take place, the Moon is an open and uninterrupted history book spanning some 4 billion years. And once you know that markers to look for, you will find features that are among the oldest and the newest right beside each other.

The thread also discusses lunar libration the Les mentioned, and how it can be used to advantage to observe features that are along the limb.

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Old 25-08-2019, 11:01 AM
Brown.dog (Tony)
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Thanks Alex and Allan,

Thanks for the link. I'm really excited to explore all the moon and see all those features you mentioned, I can't see it being boring at all. Also, I am really keen to view the areas that the Apollo missions landed and just muse on the fact that men have walked around there.


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