Keith Powell's Town Views of the Stars

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style 1 (8+1 views) and style 2 (one view) and style 3 (8 views)

Briefly...

This program shows the brightest stars in the sky which, if you have adjusted the settings accordingly, are the stars you should see at this moment if you look up from your screen and gaze out of a window. Naturally, this assumes that it it dark and that there are no clouds or objects to obscure your view.

The program is displayed differently on three web pages, and links to these are provided above. The first assumes you can display a wide window on your screen but it shows everything provided by the program and the third requires a slightly narrower window because it omits one of the views of the stars. The second is intended for a small screen because it only shows one view.

Each of the windows shows one or more tall rectangles, and under each rectangle is a compass direction. If the direction in which you will gaze allows you to see the stars to the North-East, you will use a rectangle which is annotated NE. Each rectangle shows the view through an angle of 25° to each side of the centre of your view. It shows the horizon at the bottom and, in the centre of the top of the rectangle it shows the point above your head, although the rectangle has been extended a little to show a tiny bit of the sky behind you. This can be quite convenient if you decide to go outside (and don't have a bad neck).

Origins

I wrote this program because I wanted to display in a clear way only the stars I could see when I was in a location having lots of street lighting. Because these lights illuminate the sky even on what seems to be a really clear night, I was able to see so few stars I couldn't identify most of them. Although I could see many more stars using binoculars, the field of view was inadequate and didn't help me with the identification.

I buy the annual guides to the stars each year but I find that the 12 monthly views of the stars they provide need a lot of thought before I can be certain which of the 12 star-maps applies best for say, 7pm in late November or 4.30am (during a disturbed night) in early February. The fact that some of the star maps take daylight saving time into consideration is a complication. Also, planispheres are difficult to use to identify the stars in, say, the South-West because of their inherent curved azimuthal distortion, and they show far too many distracting stars I can't see in the sky. I therefore wanted an application which would display only the brightest stars, and these in a clear way in directions other than North or South. Further, I wanted it to show the positions of the stars at the current instant of time, that is, the date and time displayed by my computer clock, suitably corrected.

Eventually, I achieved my aim. Using my prototype, I printed out the views in the 8 prime compass directions for the current time and dashed outside where the cloudless sky (misleadingly) appeared to be crystal clear. Unfortunately, only 10 metres away from my front door is a street light, and the whole sky was unobtrusively illuminated to some extent by the city lights.

I held up the printout to shield my eyes from the glare of the street light as I wandered around, searching for the best view in each of the 8 directions. (I got some strange looks from people walking their dogs.) I also had to go to the back of my house at one stage, of course. It took me about 35minutes to identify and tick on the paper every star I could see in the sky, apart from two. I didn't even need a torch for this operation! The two I hadn't identified turned out to be planets, and my prototype version didn't show these. I found I had identified every star shown on the (now damp) paper that was more than about 25° above the horizon, and some that were below that. I was 'over the moon' with excitement! (Well, actually, the printout didn't show the moon at that time, either.)

Since then, the application has been slowly enhanced. (I wanted to name it 'City Stars' but was disappointed to learn that in most people's minds this refers to the football stars who play for Manchester City.)

There are now 3 versions which use slider bars, buttons and even a little menu (I ran out of space for more buttons).

Description of the rectangular views

The bottom of each rectangle shows the horizon. The rectangle reaches up to your Zenith (the point directly over your head) and is extended a little way beyond, down towards the opposite point on the horizon. If you have a bad back or neck, use a deck-chair or lounger to see the stars up there. These views are 50° wide, including at the Zenith. The view at the bottom of each rectangle overlaps a little with the view of its neighbours and overlaps a great deal at the top. The two curves forming an arch in each rectangle show the points at which each view touches the matching points on the arches of its neighbours. Stars close to the Zenith appear around the Zeniths of all the views.

The stars shown are basically the hundred brightest stars in the sky, plus a few which I find useful in highlighting features of the constellations. The Sun, Moon and 5 brightest planets are also shown, these being drawn as black circles filled with red. The almost straight dotted lines show the position of the Celestial Equator, angles along it from the First Point of Aries being shown. Incidentally, to find the Right Ascension (RA) of a planet, imagine a line through the planet at right-angles to the dotted line. Its RA is the point where the imagined line meets the Celestial Equator. The planet's declination is roughly proportional to its distance along that imagined line.

The arches drawn in the 8 prime views indicate the azimuths which are 22.5° to each side of the central direction of the view. Thus, in the Northern view, they represent azimuths of NNW and NNE. The equivalent curves in the single view show the azimuths extending from the horizon in directions marked under them. These azimuth curves all meet at the Zenith, which is the point at the top of the main part of the rectangle, although the rectangle has been extended a little above this which allows stars just on the other side of the Zenith to be shown. This allows the stars overhead to be more clearly depicted. Consequently, stars within 20° of the Zenith appear in every view.

Although the stars are shown here right through the day, they can only be seen when it is dark and when clouds do not obscure the view. When the Sun and Moon are above the horizon, they can almost always be seen, if the clouds allow. Historians will note how well the Moon, which, during the first quarter, can be seen both during the afternoon and, a few hours later, during the evening, was used as an intermediary when determining the position of the Sun along the circle of the zodiac.

The Three Versions

Three versions of the application are provided here. The first version is intended for equipment which can display a very wide applet. The third version is intended for a slightly narrower display. The second version requires only a narrow display which is not very high. Hopefully, one of these will adequately serve your needs, and I hope you will forgive me for describing the three versions in reverse order.

The Third Version

The third version (newindex3.html) shows 8 different rectangular views, each in a different compass direction. However, because I wanted to display the views from West through North to the East at the top, and from East through South to the West under these, that meant duplicating the East and West views, so I actually display 10 rectangular views.

The long slider-bar to the left contains a red spot indicating the currently selected latitude, and clicking in this rectangle elsewhere alters the setting. Conversely, you can drag the spot to any latitude from 89° away from the equator, North or South, to about 2° from it. The resolution of the setting is 1°.

Underneath this is a button allowing you to change the hemisphere, so that the selected latitude can be to the North or South of the equator.

There are also longitude adjustment buttons which allow you to set your distance from the longitude used for your time-zone.

The Second Version

The second version (newindex2.html) only shows one view and therefore it uses the smallest window of the three. However, the direction of this view can be changed using the long slider-bar below it. There are buttons above this slider-bar indicating different directions, and the compass directions annotated in these buttons indicate the positions of the compass directions of the red spot in the long rectangle beneath them. You can click on a button to select a direction, or you can click in the slider-bar to select a different one. You can also drag the spot along, the spot moving in 3° steps.

The setting can be seen directly underneath the rectangle showing the view of the stars. You can adjust the other features - latitude, hemisphere, longitude adjustment - in the same way as was described above.

The First Version

The first version (newstars.html) is merely a composite of the other two versions. It has the 10 rectangles showing the views of the stars in the prime compass directions and to the left of these is the rectangle showing the view in any selected direction. The slider-bar on the left selects the latitude in conjunction with the hemisphere button, and the slider-bar under the rectangle selects the compass direction of its view.

The first version is probably the most fun. Experiment by dragging the latitude red spot up and down, and click on the hemisphere button. Then try dragging the direction red spot from end to end, Try the three buttons which switch the names of the constellations, stars and planets on and off. You will also find that altering the Longitude adjustment in 1° steps seemingly alters the apparent time in 4minute steps. That is, a star or planet which has just set will set in 4minutes' time for an observer 1° to your West.

Comments and Limitations

If you are lucky-enough to live close to the meridian that is used for the clocks in your area of the world, you needn't worry about the longitude setting. Otherwise, there are buttons which allow you to make a longitude adjustment.

For instance, if you live in Eastern Spain, the time indicated by your watch is based on the meridian which runs through The Czech Republic so you will need a longitude adjustment of -15°. If you live in Central Spain, whose longitude is a further 4° from The Czech Republic, you need a setting of -19°. Similarly, in the West of Spain, you need an adjustment of yet another 4°, meaning an adjustment of -23°. During Daylight Saving Time, the program automatically adjusts for it, subtracting the equivalent of 15° longitude.

Curiously, the time indicated by an old sundial in Western Spain is about 2.5 hours in error compared with the time indicated by your watch when it is showing Spanish Summer Time. (This sundial error also varies by up to about a quarter of an hour according to the Equation of Time.)

When these settings suit your location, the views in the rectangles show the brightest stars and planets in the sky (assuming it is dark-enough, and the sky is seemingly clear) when looking in the 8 prime compass directions or in the selected direction. Thus the rectangle marked SE shows the stars which are above - and up to 25° to each side - of the south-eastern point on your horizon. As indicated above, the stars shown are only the brightest stars in the sky, and if you live in a town or city these are probably the only stars you can see (without binoculars) because of your street lighting. Each star is identified with its common name, if it has one, and one of the stars in each constellation has the constellation name alongside it. When a pair of stars in a constellation are both shown in the same rectangle, a line joins them. The Sun, Moon and the 5 planets visible without binoculars are highlighted by using a large black circle filled with red, and their names are initially shown alongside. Buttons are provided which allow the names of the stars, constellations and/or planets to be switched on and off.

The latitude slider-bar allows you to set your latitude quite accurately. However, the limited accuracies of the algorithms used in the program do not warrant a setting of better than 1°. You may notice that this program can't display the views for latitudes within a degree or two of 90°North, 0° or 90°South. (Typically, the program can't cope with zero divided by zero.) If you try to select one of these three settings, the program automatically adjusts your latitude selection accordingly. Unfortunately, that limitation still doesn't eliminate one occasional 'bug' so I am thinking of drawing little bushes all around the horizon, which should hide the problem.

I find it irresistible to experiment by selecting latitude settings of 89°North, 89°South and latitudes close to the Equator, so that I can see the stars visible from those locations. Together, the first two show all the bright stars in the sky. When you select a latitude of, say, 2°, you can see a half of the visible stars at any time, but over the course of a full night, you see virtually every star in the sky. Of course, it is difficult to see the stars close to the horizon.

Should you wish to use the applet often, you may be interested in the html files which load it. If you make a copy of the one of these you prefer to use, you can change the parameter values according to the latitude and the longitude difference of your location. These settings will then be used whenever the program is first loaded.

Keith.

You can email me at (Sorry, you can't click on this.)