IOtMN occurs annually in September or October, when the Moon is around first quarter ― a great phase for evening observing. A first-quarter Moon offers excellent viewing opportunities along the terminator (the line between night and day), where shadows enhance the Moon’s cratered landscape. This year’s event is officially Saturday, September 19th, one day after first quarter.

Follow the first link above to visit the NASA IOtMN website with a rich selection of resources, viewing tips and detailed maps of the lunar surface highlighting the best targets for viewing. For a detailed map of the moon on that night, check out this interactive page. There is also a downloadable map set with specific easy to view surface features and locations of the six Apollo landing sites.

You can enjoy the magic if viewing the moon by yourself at home or in one of many events hosted by  organized groups. And the resources above are all usable every month for your own personal exploration of the Moon!

Published Sep 2, 2024, Updated Sep 12, 2026

One such detail that is only revealed at two specific times in the cycle is the so-called “Lunar Straight Wall“. This feature is one of the best examples of a linear fault, also called a rille. It measures about 110 km in length and stands about 300 meters tall. When you’re looking anywhere near Mare Nubium, it’s quite prominent as an almost straight line. However, it turns out that it is easy to see ONLY on the first day past 1st Quarter or 3rd Quarter. The reason why it’s only visible around this time is because of the shadow that it casts when struck with the sunlight at just the correct angle. For the rest of the month, it’s mostly hidden because it doesn’t create a good shadow.

I have found several references online, like the one from Wikipedia in my previous post. The Lunar Straight Wall is also known by it’s Latin name Rupes Recta. I’ve included another link below from Sky and Telescope magazine with more great images of the feature. Here, lunar observing authority Charles Wood has a great article about Rupes Recta with some very fine images of this feature.

You can find it easy enough with a small telescope of perhaps 50 mm or more. That also puts this object within reach of binoculars though you’ll need to steady your hold by bracing against something or using a tripod. Use the resources above so you know where to find it and look for it on the day after first quarter or third quarter. That’s only two nights per month, making it a little more precious of a view.

Good luck with the weather! Clear Skies! (hopefully)

Published Feb 29, 2020; Updated Sep 4, 2026

NASA has information on all of the lunar eclipses for 2026, into 2027. Their Daily Moon Guide also has details on this coming event. This NASA link has details on how and why an eclipse occurs in the first place. You will learn about our Moon’s orbit and the penumbra and umbra shadows that we can witness during an eclipse.

In-The_Sky is a very sophisticated site for observers and has a very useful guide with a simulation of the event from our local Atlanta skies. You can also get an active sky map from SkyViewCafe and you can plan your observation towards the south for the evening.

Of course an eclipse is far easier to predict than the weather but hopefully we’ll be “in the clear” for the duration of the eclipse. Keep an eye on the forecast starting late the preceding week (and keep your fingers crossed!). Assuming that sky conditions open up, make sure you have read the articles above to get the timing charts and some tips for preparation. You don’t need a telescope or even binoculars to enjoy this event.

Enjoy the time under the sky. Remember that howling is perfectly allowed, too! Good luck with the weather.

One of the most recognizable patterns in the sky is the Summer Triangle. Unlike many other asterisms that are confined to one constellation, with the Summer Triangle, you get three for the price of one! The key stars in The Triangle are as follows: Vega in the constellation Lyra (The Lyre), Deneb in Cygnus (The Swan) and Altair in Aquila (The Eagle). Vega is the brightest of the three and easy to find through the summer into early Fall. Once you get to know how the Triangle is placed in the sky, you can also use it as a guide to other prominent stars. This month, you can catch this fairly bright asterism clearing the tree tops after about 10:00PM in the eastern sky and it will stay flying overhead into October.

Follow the links above to get details on these different objects. You’ll find that the three constellations have long been associated with birds of some kind, no matter what culture is gazing up. If you’re keen to investigate the star names and their connection to ancient sky watchers, check out these two great books on star mythology Julius D.W. Staal’s “The New Patterns in the Sky” and  Richard Hinckley Allen’s “Star Names: Their Lore and Meaning”. They are two of the great modern resources for ancient astronomy.

Regardless, you can revel in the magic of the Three Mythical Birds of Summer!

Originally published 6-12-15, revised 7-15-26

Well, it’s in the North sure enough but it’s not as bright as one might think with such an important name to all of us living the northern hemisphere. However, we can use several other stars as pointers to easily find Polaris. If we can find one of the two constellations Ursa Major or Cassiopeia, we can get to Polaris easily.

Below are some links that will help you find your way to the North Star.

links:

Wikipedia - The Big Dipper as Guidepost

See how you go finding North and also finding Polaris, the North Star.

Published Feb 26, 2019; Updated May 15, 2026

As twilight progresses after sunset, the individual stars of the celestial bears gradually come into view. The brighter stars appear first of course, but the main stars in the Big Dipper are within a fairly small range of magnitude - about 1.8 down to about 2.4. In order of magnitude, you have Dubhe, Alioth, Alkaid, Mizor, Merak, Phecda. Megrez, where the handle connects to the bowl is 3.3 magnitude, but still bright enough to catch in suburban skies.

If you can see all of the Big Dipper, then you should be able to easily see Polaris at the end of the Little Dipper. It’s the brightest star in the constellation. You will also be able to see the end of the bowl of the dipper and the next brightest stars Kochab and Pherkad. The remaining stars are dimmer than 4.3 magnitude so they are much dimmer than most suburban nights will allow. But you never know your luck!

If you create a chart with these two constellations and write in the magnitudes, you will have a very useful reference to use to gauge the sky. Wikipedia has good information on all the constellations and the Celestial Bears are no exception. Follow the links below to get a lists of these stars with their magnitudes and charts that you can print to make a field reference - Big Dipper & Little Dipper. As with all the Wikipedia constellations pages, there’s also a lot of detail on the mythology and star lore of the heavens.

Published on Feb 7, 2020; Updated Apr 29, 2026

Starting with Sirius, the brightest star in the heavens, we can work around counter clockwise to Rigel, Aldebaran, Capella, Pollux, and Procyon. These are all prominent stars whose brightness shines through even a light veil of clouds. The circuit takes in the major constellations of Canis Major, Orion, Taurus, Auriga, Gemini and Canis Minor.

These stars range in magnitude from -1.5 with Sirius down to Pollux at mag 1.1. So, they are peeping out early and high overhead this time of year. As the night deepens, one can easily make out the figure of Orion, easily spotted by it’s belt of three stars. The ring of Auriga is usually next to become clear, forming it’s own circle of stars. The triangle of the face of Taurus slowly takes shape as the great expanse of the Big Dog about Sirius moves up into the southern sky like a big meat cleaver.

All these objects shine through even moderate light pollution. So, whether you’re in the suburbs or the country, you can practice your geometry using these fine beacons of the winter night, as in six, half dozen or the other! Enjoy!

first published 1-3-24; updated 3-1-26

There are different ways to describe Earth’s orbit and the orbit of the moon around our planet. Its related to the geometry and timing of those orbits. The method for describing the complete cycle of the moon phases is known as the synodic month. This is the view of the moon from Earth’s perspective and is relative to our point of view. The other method has a more general and wider viewpoint and it is known as the siderial month.

In order to get a better feel for these two concepts, it’s handy to have some kind of diagram or, even better, an animation to show the Moon phases as it orbits the Earth. If you can get your mind around the geometry from your perspective and the solar system perspective (as in the animation), it’s easier to see how “the month” is defined in both of the methods above.

Ultimately, we are talking about lunar calendar systems and there are actually quite a few. The ancient astronomers weren’t just moon gazing but trying to understand what they were looking at. Their persistence lead to what is now a very refined but kind of crazy way of showing what month it is. After all, we want everyone to know our Birthday in time or maybe we just want to take a month off!

First published 3-19-2016; Updated 2-1-26

On Jan 7, 1610, the discovery of three of Jupiter’s moons by Galileo Galilei and a fourth one on Jan 15, provided the evidence that the heliocentric theory proposed by Copernicus was indeed valid. As the details were actually put in print in Galileo’s book Siderius Nuncius (The Starry Messenger), the simple fact of this discovery was not only a wonderful revelation of nature but a complete rebuttal of the idea that the Earth was the center of … well, everything!

This so-called geocentric hypothesis had held sway since the days of Ptolemy (c. 100 – c. 170 AD). However, what Galileo clearly saw, magnified in the telescope, was another world in our solar system that had not been revealed like this before. And since the moons could be shown to orbit the planet, it meant they were NOT orbiting the Earth!! One might say that this discovery shook things up a little!

He might have seen something like this representation on January 7th through his homemade 20 power telescope. From left to right, the objects in the view are Ganymede, Jupiter, Europa, Io & Callisto.

In the simulation above, Callisto and Ganymede are the farthest out but Io and Europa are very close together. So, Galileo may not have been able to split them that first night. Nevertheless, his persistence and continued observations over the next few nights showed clearly how the moons were shifting position in relation to Jupiter itself and the entire collection was drifting against the background star field. To him, this movement of the objects were the clincher in concluding this was not just a planet, but one with orbiting moons.

This set of observations comprised one of the most consequential discoveries in the history of science. Due to Galileo’s keen sense of the importance of the observation and the empirical method he was indeed a giant of the age of modern science. Einstein himself in 1933 referred to Galileo as “the father of modern physics and in fact of the whole of modern natural science.”

That is powerful inspiration indeed.

originally posted on Jan 7, 2025

]]> http://ceastronomy.org/sbieger/posts/153/feed http://ceastronomy.org/sbieger/posts/55 http://ceastronomy.org/sbieger/posts/55#comments Thu, 01 Jan 2026 22:58:21 +0000 sbieger http://ceastronomy.org/sbieger/?p=55 It’s now well after the Winter Solstice and shorter days are still the rule; sunsets coming earlier paving the way for evening viewing and just in time for the return of Jupiter in the mid evening skies. So the shift grants even more time for catching the king of planets.

Now would be a good time to begin this season’s Jupiter viewing, coming off of the eastern horizon at 5:30 PM, EST. By late January, Jupiter will be rising much earlier and easier to catch in the evening hours.

Jupiter will be with us in the evening sky through early June. Plenty of time to explore the moons and features of our largest planet.

More on Jupiter in the coming weeks as the King of the Solar System brings another great season of Big Planet views. Stay tuned!

originally posted on 12-13-14