Steve’s Virtual Planet

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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Naked Eye Lunar Observing Pt 2

In this post, we’ll continue the discussion of naked eye targets on our Moon. In the first post, we looked at some of the larger mare that present themselves during the week from new moon to 1st quarter. Let’s “follow the terminator” and look for some more challenging objects to be found during the week up to 1st Qtr. We’ll use some of the so called “Pickering Dozen” to add to the hunt. I’ll call them “P12″ for short.

When the moon is illuminated “half way” on the right side, there are fewer of the prominent craters that appear later on. However, if you have located Mare Serenitatis and Mare Tranquillitatis, you can use these to find some more challenging mountains and regions on their edges. Between these two large features is a thinning kind of peninsula known as the Plinius Region, named for the crater in its vicinity, Plinius. You should be able to make out this feature to the left of the field at the juncture of both of these large features.

Another of the P12 is immediately to the left. Mare Vaporum, The Sea of Vapors. At first quarter, this feature will be just to the right of the terminator just above the equator. It’s a smaller mare that looks a bit like an extension of Serenitatis to the south west.  That will be our reference point next time when we hike the Apennine Mountains!

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Naked Eye Lunar Observing Pt 1

This is the first of (hopefully) several posts that discuss naked eye targets on our Moon. Instead of a map or a geographical approach, I’ll “follow the terminator”, the shadow line that progresses across the moon’s surface as the phases advance.

For some easy targets, why not start with the Lunar Mare (maria is singular), those dark and typically large areas on the lunar surface. Before the time of Galileo, most people thought these dark areas were “seas”, hence the name. Now we know they are large flat (dry) plains of fairly smooth basalt that formed 3-4 billion years ago from early volcanic activity.

It’s best to get a small moon map in front of you so you can get oriented. The are downloadable ones like this one from S&T with a printable map on page 10 or this image with different sizes for different screens.

With map in front of you, work from the right back towards the left. This is the way the moon will be revealed as the phases progress from New Moon to Full Moon. It is also the first half of the moon’s full cycle that is visible in the evening. The first obvious object you can see even within the first week is Mare Crisium. As the nights pass, you will then see more of the Mare (The Sea of) - Fecunditatis (fertitility), Tranquillitatis (tranquility), Serenitatis (serenity). By the time of the First Quarter, you will be able to see all of those features.

In the next post, we’ll look for some more challenging objects to be found during the week up to 1st Qtr.

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How long is a month?

If you check deeper into the meaning of “month”, you quickly find Earth’s moon right at the center of the explanation. It turns out that the ancient Babylonians pretty much started this examination in the years around 500BC. These early mathematicians and astronomers took extra care in watching and noting the movement of the moon. They came up with several methods and terms to show how the moon tracked around the Earth and how long it took.

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!

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Autumn targets sans planets

These last couple of months have seen the gradual westward track of Saturn. It’s way too early in the year for observing Jupiter. Uranus and Neptune are up later but they aren’t easy to get in a small scope. The evenings are getting dark a little sooner now, so, why not work on finding other nice objects to look at.

Well, check the Messier catalog first. A few choices there. Maybe a planetary nebula or two. Check. Galaxies? Yep. How ’bout stars with color. Yep. Several of those to enjoy. Of course, there’s always the standby - double stars! You never run out of them. The links below will take you to Wikipedia for more details. So, here goes.

First, the Messier objects - M57, the Ring Nebula still one of the best planetary nebula; M11, The Wild Duck (open) Cluster in Aquila, a good wide angle object for binoculars or low power scopes; M45, The Pleiades, another great open cluster, is up later in the evening. For galaxies, there is of course M31, The Andromeda Galaxy. And if you look lots of stars in one view, you can’t go wrong with two of the best globular clusters - M13 in Hercules and M15 in Pegasus.

Two other planetary nebula are in the NGC Catalog and high overhead - The Blinking Planetary (NGC6826) in Cygnus and The Blue Snowball (NGC7662) in Andromeda. Both are slightly brighter than M57, but they benefit from averted vision. So look off to the side slightly in your field of view to get a better view.

For colorful objects, you’ll be seeing red! There’s Herschel’s Garnet Star in Cepheus, a very nice red super giant star; there’s also Antares in Scorpius, and also Arcturus in Bootes, both a very noticeable orange.

Finally, for doubles, there’s Albireo, in Cygnus and Kappa Her in Hercules. Enjoy!!!

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