Steve’s Virtual Planet

SVC Tip #6 - Preferential treatment!

As you may have figured out by now, I have been using Sky View Cafe for quite a while. Occasionally, I find something new (or quirky) so I thought I would bring a few things to your attention.

First, I like to set the calendar tab as my default view since I want check the moon phase and to choose the day first anyhow. This can easily be done using the blue button up on the right hand corner marked “More …“. When you click it, you get … more (of course), including a set of “preferences”, Just select the little gear icon and click. The second field allows you to set the Default view. Easy.

Next, I found a couple of quirks, one being that even though there seems to be some printer settings I have had no luck with any printing feature at all. So, you may have to look for other tools for this. Finally, even though the built-in Help is really good, you may need help finding it. The help link up in the right hand pane seems broken. So, instead, use the Help ? link up in the very top center or the one in the More … button. Viola! More easy!

I hope you are enjoying SVC as much as I am. If so, check out the other tips here SVC Tip #1 & SVC Tip #2 & SVC Tip #3, SVC Tip #4 and Tip #5.

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Viewing the Lunar Straight Wall

One of the interesting aspects of observing our Moon is that many features are only visible during certain times within the full cyclic phasing of the moon. Details come and go depending on the angle of sunlight reflecting off the lunar surface and coming back to Earth. As Galileo noticed over 400 years ago, the shadow line (known as the Terminator) moves across the lunar landscape and illuminates the surface differently as it progresses across. He even used this phenomena as a tool for measuring the height of lunar features.

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. 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 virtually 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. So, for the next two months, those dates are - March 3 and 17, April 2 and 15 and May 15, and a bonus view on May 30.

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

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Gauging the sky with the Great Dippers

This time of year is a great time to reconnect with The Big Dipper in Ursa Major and it’s cousin the Little Dipper, in Ursa Minor. Even though Daylight Savings Time is going push dusk well into the evening, you will still be able to follow these great asterisms into early night as they climb over the trees.

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.

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Moon tools Pt 1 (The Intro)

I’m a tool kinda guy. You know .. Swiss Army knife, a good flashlight, some vice grips, and, of course, a good astronomy app. Web based tools and apps for astronomy and stargazing are really the good stuff. This series is going to delve into various tools I’ve found on the web that help understand our moon better. This is part one, which, implies additional parts, theoretically. So, we’ll see how my research goes and how many tools we find.

Bar none, my favorite web site is still Sky View Cafe (SVC). You can see some of my other posts with details on the features, but my main tip here is to set your SVC startup view to be the calendar instead of the default Sky view. This is easy to do using the “More…” button up in the right corner.  Click on more and then on Preferences. Change the second setting value to Calendar and then click OK. This will set the applet to go to the calendar whenever it starts. From here, the moon phases are in full display with a graphic for each day.

In one of my previous postings, I featured an animation to show the Moon orbiting the Earth. This is a great applet from The University of Nebraska that has three different views of the effect of lunar phases from Earth’s perspective. At the same website, I also found a really useful animation that shows how the effect of the moon’s gravity and our proximity to the sun sets up the tides.

See how far you get with these suggestions. You can even howl if you like!!

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Magnitude? Yes! (apparently)

Yes, indeed! Apparently! That’s how we see a star’s brightness form our perspective here on Earth. We use the term “magnitude” to describe the brightness of a star. We call the measurement of the brightness from Earth the “apparent magnitude“. The effect of this apparent brightness leads us to the more exacting method of using a numbered scale to quantify what we see. And this scale goes all the way back to the days of ancient Greece and is credited to a very clever mathematician named Hipparchus.

Hipparchus came up with a six level scale based on naked eye brightness that is still largely the same today. In this scale, the number 1 is given to the brightest stars, with a gradual decrease in brightness shown with a higher number from 2 to 6. Yes, the number gets higher as the stars gets dimmer. It’s a purely arbitrary system that has been the convention since about 150 BC.

When you use a typical sky map or star chart, look for the legend that shows a row of different diameter dots with a set of numbers on them. SkyMap uses a scale from -1 to 4 for its range. Other maps sometimes extend the range down to 6 or 7.

In one of my earlier posts, I examined several properties of stars such as mass and size. I will leave that line of research to you but it does have some relation to the topic at hand. However, from a star gazer’s perspective, we don’t have to delve too deep into astrophysics to work with this brightness scale. The value for apparent magnitude is found in star charts and tables of the stars as well. In some cases it is otherwise listed as “visual magnitude”, which means the same thing.

In any case, stellar brightness from -1 down to about 4 is the typical range in the suburbs. If you’re out in the country and have a really dark site, you will likely get down to around 6 magnitude, perhaps even to 6.5. And don’t forget to get your eyes adapted to the darker conditions for a better experience looking for these dimmer objects.

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Stellar size and magnitude

A while ago, I got a great question from one of my students in the Emory class - what does a star’s size got to do with its magnitude? And as she later explained, the words “size” and “magnitude” mean almost the same thing. They are similar, in our common usage, however, we talking specifically about their use in astronomy. It was clear this was a question more about semantics.

So I decided to dig further to come up with a better distinction between these two terms. But I have to start first with a third word, at the risk of further tangling this whole response. That word is mass. When we talk about stars, we start with mass. Stuff. What stars are made of, mostly hydrogen as it turns out.

The terms magnitude and size differ from the term mass. They are interrelated to some degree but in a straightforward linear way. But we always start with mass when considering a star’s properties and then go from there.

Astronomical magnitude, in the sense of what we see, actually refers to apparent magnitude. It is a measurement of the “apparent” brightness of the star as seen from Earth.In the days of the famous Greek astronomer, magnitude meant “bigness”. However, by the mid-nineteenth century it was determined that stars were so far away that no accurate measurement could be made of any starts size.

Sometimes the word mass is interchanged with size. But mass doesn’t always translate directly to the physical size of a star. Our sun, for example, is slowly loosing mass over it’s lifetime but once it nears the end of its life and becomes a red giant, it will be much larger in terms of its physical size, namely its diameter.

There is far too much to say about stars in this blog from the point of view of astrophysics, but if you wish indulge try any of these web pages below for further reading.

List of stellar angular diameters

Universetoday: Size-of-Stars

ClassZone: A Stars Size

Stellar Mass

Astronomical Magnitude

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Finding Polaris

A common question arises about sky watching that I wanted to address, namely, “How do I find Polaris, the North Star”? It’s a great question as well as it is often asked. For many people, the first assumption about Polaris is that it is a bright star so it should be easy to see. And, of course, it’s the North Star so it should be in the North, right?

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

FVAC - Finding your way in the sky

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

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Lunar Eclipse - January 20-21!!!

This year starts off nicely with a lunar eclipse on January 20. This is a Sunday night during the MLK 3 day weekend and it will be visible to all of North America. The first stage with the penumbra visible is starting Jan 20 at 10:10PM (22:11) EST and last visible at 2:15AM (02:15) EST Jan 21.

There are two great articles from Sky & Telescope and Astronomy with details on the event. Sky & Telescope has all of the solar and lunar eclipses for 2019. There’s lots of explanatory stuff before the details for the January eclipse, about half way down the page. Astronomy breaks down the event and places it among all the major objects in the southern sky during the entire evening. So the sky map in the article is worth a study before hand.

Of course all of that is grand stuff and 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 weather 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. A pair of eye balls, a thermos of hot tee and some warm layers should be sufficient. Remember that you will get a chill quickly just standing around in the winter night. Things progress slowly during a lunar eclipse so you can even run inside if you get cold and then reemerge later not having missed much.

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

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Back for another year!

Welcome all to a new year and a new perspective. I feel inspired to move forward and to share my passion for astronomy with the outside world again for another year. There is much to revel in this coming year including the lunar eclipse on January 20! Check my next post for details. I hope to get some of my astro projects up and running, especially with my research on ethnoastronomy and archeoastronomy.

I also plan (again) to take this astronomy blog site to the next level in the coming months. I’ll be focused on completing the series on naked eye lunar observing and moon tools. I am also gathering some external online content on Solar Dynamics and Space Weather as a bonus, ya know, in my spare time. Stick around and watch this space for more stuff soon.

In any case, here is wishing you Clear Skies!

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SVC Tip #5 - New Features

Here’s another update in the series on using Sky View Cafe (SVC) and some details on the recent upgrade of this tool. Kerry Shetline has released the latest upgrade as of July 2017 with a slightly different look but it replaces the legacy Java version. There have been some refinements but it’s still the very familiar tool compared to the old one. The current version as of this writing is 1.4.14.

Java is not used any longer (yay!) so this means you won’t have those annoying instances of the tool just dying because a new security fix is needed.

There is an extensive help page but use the link within the “More …” button. Most things are fairly intuitive but there are likely things you don’t catch without a lot of trial and error.

Have a great time with SVC and check out the other tips here SVC Tip #1 & SVC Tip #2 & SVC Tip #3 & SVC Tip #4

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