Saturn reaches opposition on February 23rd! Rather than prattle on about it for paragraphs and paragraphs I’ll point you to the Universe Today blog site. The Universe Today is one of the better astronomy blogs. They also publish regular and very interesting podcasts. Check them out!

Since last post I’ve had to back off a tad from new developments with Star Atlas. Reason:- My Sidereal Clock wasn’t keeping proper time! Now, it wasn’t just out a constant few seconds or even a constant few minutes. No, my Sidereal Time seemed to be further and further off the mark the longer my program ran! Not a great amount but enough to make the star positions inaccurate after just a few minutes.

Now, I’m glad you’re asking, “What is Sidereal Time and why is it important?”. Sidereal Time is time measured by the stars. The time we use everyday (the time kept by our watches) is called Local Mean Time (LMT) and is derived from Local Apparent Time and… well, its all based on the position of the Sun. Sidereal Time, on the other hand is time based on the position of the stars. If you were to look at a bright star in your night sky (say Alpha Orionis or Betelgeuse in Orion) and record it’s altitude and azimuth (position in the sky) at a given time you would find that on the next evening the star would reach that same point 4 minutes earlier (by your LMT or your “watch” time). So, your Sidereal Clock is running approximately four minutes faster than your LMT clock.

Now, to calculate the instantaneous position of a star in your night sky you need to know the Right Ascension and Declination (sort of the Lat and Long) of the star, your Longitude, your Latitude, and your Sidereal Time (derived from your Coordinated Universal Time (UTC) and your Julian Date). In computer speak, here are the formulas:-

Julian Date = 367 * CurrentUTC.Year – Math.Floor(7 * (CurrentUTC.Year + Math.Floor((CurrentUTC.Month + 9) / 12)) / 4) + Math.Floor(275 * CurrentUTC.Month / 9) + CurrentUTC.Day – 730531.5 + (CurrentUTC.Hour + CurrentUTC.Minute / 60 + CurrentUTC.Second / 3600) / 24

Mean Sidereal Time = 280.46061837 + 360.98564736629 * Julian Date + Longitude

(Math.Floor simply means take the nearest integer (non-decimal) value.

So, you can see why I might have goofed a bit on originally coding them. Anyway, all is well now; well, almost. This particular version of the Mean Sidereal Time formulas will keep my Sidereal Clock accurate to within 0.001 seconds for the next 10 years but will only be accurate to 0.1 seconds a hundred years from now. Such is life; more accurate formulas are needed. Stay tuned.

So, after fixing up the Sidereal Time issue I added one new feature and one new improvement. I redesigned my splash screen (the screen that displays on program start) to look a tad niftier and I coded the feature that allows the program to be used from anyplace on the face of the earth! Yep, you can now select one of 850 cities (facilities for user defined locations and locations read from a GPS will be added soon) and you will see the night sky configuration for the current time in that city.

The latest updates added to my Star Atlas Planetarium sofware:-

User Selectable Date and Time

The time and date can now be changed by the user. Up until now the application would read the system time and display the position of the stars, in real time, based on the time offered by the system clock. The user can now select any date/time combination from January 1, 1753 to December 31, 9998. The caveat being, of course that for dates far from the epoch date (year 2000) of the stars in the star catalog the less accurate the star positions are. But, for reasonable deviations from the year 2000 this is not a problem. Future versions of Star Atlas will recalculate the epoch date if the deviation from the default epoch is too great. Once the user date has been selected the sky will, of course, change in real time as if it were actually that day and time.

The usefulness of this feature is that the user can now choose to see the sky at the time of their choosing. Its really cool, for e.g., to look at the sky on the date and time you were born, or to create a star chart based on some evening next month, etc, etc.

Sky Animations (Time Warping)

This feature is really cool. From the currently selected date and time the user can choose to advance the sky any number or combination of years, months, days, hours, and minutes. The refresh rate of the display is selectable from a fast update setting of 10 milliseconds to incremental update settings from 1 to 10 seconds. The upshot is that the user can advance (or reverse) time as the need arises. So, for example, the user may be viewing the sky on January 22, 2008, at 5:00 PM but might be interested in finding out when the belt stars in Orion cross the southern meridian. The user would simply configure and run an animation to advance the sky in say 4 minute steps every 1 second and then watch for the time when Orion’s belt crosses the meridian. Running the animation would cause the sky display to change every second with the time (and the star positions) advancing by 4 minutes with each display refresh. Its hard to describe in words but essentially the operation gives an animated view of the stars moving through the sky in “sped up” time.

I tried to make some movies of these new features but, alas, YouTube strips out too much detail and makes the videos to small for full screen views of Star Atlas to be meaningful. You’ll just have to wait for the first beta release of Star Atlas to experience the joy and elation brought on by Sky Animations!

Clear Skies!

Things are moving along nicely with my planetarium software project. Some improvements since last post:-

• Constellation names are now being displayed and can be turned on and off.
• Constellation lines can be turned on or off.
• The local horizon can be turned on or off and can be displayed separately from the Alt/Az grid.
• The local meridian can be turned on or off (with 10 degree tick marks) and can be displayed separately from the Alt/Az grid.
• Zoom in and zoom out are enabled.

Following is a screen shot of Star Atlas looking south from Halifax at approx. 1:45 AM on December 29. The Local horizon (curved green line at the bottom) and the local meridian (vertical line, very faint in the screen capture, with the tick marks) are visible.

A beta release may soon be available for friends and family!

(Click for a larger image)

Well, I’ve been away from my blogs for a bit. Reason:- I’m writing a planetarium application and, bloody hell, its taken over my life!! The following is a picture of the opening screen. What are you seeing? Well, you’re looking West into the night sky from Halifax, NS. Above the green line are stars that are visible above our horizon (at the moment this screen capture was taken) and below the line are stars below our horizon and, therefore, not visible from our location at the moment. The green lines, including the dark green horizon line are lines of Altitude and Azimuth (ALT/AZ); they indicate a stars position above the horizon and its angular distance around the horizon from North. The white lines indicate Right Ascension and Declination (RA/DEC) lines. RA/DEC is like Latitude and Longitude for stars. The bright white RA/DEC lines indicate zero hours RA (the one going up at 45 degrees in this image) and(the smiley faced one) zero degrees DEC. The ALT/AZ position of a star will change in real time whereas the RA/DEC position of a star will not change appreciably over the span of human lifetimes.

So far I have limited features enabled. I can turn any of the grids (or constellation lines) on or off, display the stars in real time (their positions will change with respect to the local horizon in time with the computer system clock), I can choose to look North, South, East, or West or scroll the globe 360 degrees in any direction or even display the Zenith (the point directly overhead) in the center of the globe. This is a useful feature in that it puts the local horizon around the perimeter of the globe and effectively creates an instantaneous star map of the stars and constellations in the night (or daytime) sky for any instant of time.

There’s still loads of work to do on this project. When completed, the user will be able to zoom in on any area of the sky, will be able to track planets, comets, satellites, view the positions of galaxies, globular clusters, planetary nebulae, etc, etc. At the moment the application uses only the Yale Bright Star Catalog (9,110 objects) as its data source but I have plans of adding at least the 2.5 million object Tycho Star Catalog. Oh, of course, it will eventually display the stars as they would look from any point on the Earth’s surface (I may even enable GPS capabilities to make this feature more accurate). So far its been engrossing, educational, and just plain lots of fun!

(Click the image for a larger view. It looks infinitely better when its not a JPG image!!)

There are billions and billions of galaxies in our universe and they come in all shapes and sizes. I kinda like the shape of this one known commonly as the Pizza Dough Galaxy or formally as ESO 510-G13. The Galaxy is located in the constellation Hydra, the largest of the 88 constellations.

Open this post and click for a PDF of Jupiter Ephemerides 2008

Alas, I post this only as a teaser! Tonight (November 11, 2007) at 23:38 LMT (ADT) two of Jupiter’s Moons, Io and Europa, will pass across the face of the giant gas planet. Jupiter will have long set in the Western sky by the time the event happens but, if the planet were visible, we would not only see the moons crossing the face of the planet but also the shadows of each of the moons.

So, why post this if we can’t see it? ‘Cause I think these events are so awesomely cool! Shadow transits are quite common and fun to watch. You’ll need a telescope of at least 100 mm (4 inches) in aperture, a dark sky, and good seeing conditions to observe the event but after you’ve seen your first one, you’re hooked. Unfortunately, Jupiter will reach superior conjunction (on the other side of the sun from Earth) on December 23 so for the rest of this year the planet will either be to close to the sun (visually) for optimal viewing or will not be visible at all. The planet won’t return for optimal viewing until late spring, summer, and early fall of 2008. Even then, Jupiter will reach a max altitude above the Southern horizon of only slightly more than 20 degrees (as observed from mid northern latitudes).

But, if we could see this evenings event it would look something like the following video. The clip is about 2 minutes long with the first minute in real time and the second minute sped up 300 times. The entire event from Io’s shadow becoming visible to Io’s shadow disappearing takes slightly more than two hours in real time.

The video was created with Starry Night Digital Download 6 from Imaginova.

Solar System in November has been updated. Click on “WhatsUp” under Categories in the left panel to see the entire post.

I’ll be editing and adding to this post over the next few days so stay tuned!

Observations are for roughly Nova Scotia, Canada (Time in AST and roughly 45 deg N Latitude)

Sun

On November 1 the sun is just inside the western border of Libra and will move through Libra, through Scorpius and come to rest, on November 30, on the boundary between Scorpius and Ophiuchus (o-phee-ooo-kus). Yes, all you astrologers, the sun actually passes through 13 constellations not 12; deal with it!

Mercury

Mercury orbits very close to the sun and at the best of times is a difficult planet to observe. However, early in November Mercury will reach its greatest western elongation (the angle between the sun and the planet as viewed from earth) of 19 degrees. The planet will be visible just above the east-southeast horizon just before sunrise. I would caution inexperienced observers from searching for this planet with binoculars or a small telescope; you don’t want old Sol to pop up over the horizon and appear in your field of view!

Venus

At mid-month Venus will rise at about 3:00 AM, will transit (be in the south and reach its highest point in the sky) at about 9:00 AM (at which time it will be about 44 degrees above the due south horizon) and will set at roughly 3:00 PM. For those who rise before sunrise (roughly 7:15 AM), Venus should be easily visible in the south eastern sky. You can’t miss it; save for the moon, it will be the brightest object in the sky at that time of day. The planet will reach perihelion (closest approach to the sun) on November 30 at which time it will be about 66.8 million miles (107.5 million kms) from from old Sol.

Mars

Something very special is happening with Mars this month but you’ll have to be vigilant to see it. Planets normally move from West to East across the starry background but at about mid month Mars will appear to stop its West to East motion and begin to move East to West! The planet will continue to move East to West until the end of January 2008 at which time it will stop briefly and then resume its normal West to East movement. The phenomena is easily observed but will require that you observe Mars and note its position against the stars over a period of time. So, at the beginning of the month, Mars will be in the Western side of Gemini heading for the center of the constellation. Then, at about the 15th of the month, Mars will appear to stop briefly then start off in the other direction – towards Taurus. When it reaches about the middle of the horns of Taurus (January 31, 2008), Mars will pause again then reverse its direction and head, once again, towards the East. The following video illustrates the movement of Mars against the stars from about September 1, 2007 until about mid May 2008. (The white object you see flashing through the field is the Moon; just ignore it.)

So, what’s happening here? The phenomena is called Mars Retrograde Motion and the explanation is fairly simple. Mars is a superior planet (further away from the sun than earth) and therefore orbits the sun a bit more slowly than the Earth. It takes Mars approximately 686 Earth days to get around the sun as compared to Earth’s 365 days. So, about every 26 months or so we catch up to and pass Mars in its orbit and thats what we’re seeing here. Think of the Earth and Mars as two race cars going around a circular track with the faster car (Earth) on the inside lane overtaking the slower car (Mars) on the outside lane.

Where do we find this beautiful planet, you ask? At my location in Eastern Canada, Mars will rise in the North East at about 8:30 PM ADST and will not set until after sunrise the next morning. Look for the constellation Orion (he’ll be lying on his side at that time of the evening) and just follow a straight line from his upraised right arm to Gemini and Mars! (Of course, if you look for Orion later in the evening he’ll be standing up!). Click the image to see it full size.