Easy-to-read alt-az star chart customised for own location

[Andrew C]

Hello All,

Some time back, I attended an astronomy presentation session locally at which the presenter illustrated his talk with a set of four star maps that he had developed himself showing the easily visible stars and constellations for that month and approximate time in the evening in the four cardinal directions (N,S,E,W), from the horizon up to about 60 degrees altitude – i.e. ALT AZ star charts. He had sketched the positions on the maps by eye, and had included just the right amount of detail. Each person was given copies.

This approach worked well with the audience (an average bunch of interested but non-experienced locals), who would have struggled to use a planisphere because of the inevitable associated distortions and the clutter (or lack) of detail that always seems to be a feature of those charts.

I decided to see what I could find on the web to do a similar thing in software, and was unable to locate anything that came close to being readily usable, so I decided to develop my own.

The result is shown by way of example in the attached set of Excel spreadsheets and XY scatter charts, which are configured for my home location (Alice Springs) for 9.30pm local time at mid January. As I have an interest in video astronomy, I have included objects that suit that as well as eyepiece observation.

I have one set for each month (which effectively gives object positions to the nearest hour throughout the year - which is ample for bright objects visible by eye), and apart from tweaking the position of fast moving planets (or omitting them), or adding new objects, these are good from year to year. Name labels for individual objects are generated from the spreadsheet using a freeware add-on for Excel called XYChartLabeler after each chart is generated and scaled in the Excel XY scatter chart function. Icons, lines and other information labels are added manually to suit personal taste, and all labels are repositioned or resized within the chart as necessary to improve readability.

Distortion of shapes and distances is largely confined to the higher altitudes (much like high latitude shapes and areas on typical maps that attempt to project most of the world on one map), and I have reduced the effect of that by copying some shapes from low altitude to high altitude in a few cases.

Without going into detail at this stage (I can do that later if people are interested to modify to suit their own needs), the charts work well, and can be customised for any location, time of day or set of objects. The spreadsheets could also be adapted for charting much smaller parts of the sky at an appropriately larger scale. In the example, I have included the underlying formulas for all the months, but derived the charts only for January. They make deciding what is worth looking at on a given night, and actually finding it, and conveying some sense of what is in the night sky to others, a whole lot easier.

Cheers,

Andrew

[alistairsam]

Hi Andrew,

thats an excellent chart.
I was able to understand it to a certain extent, but it would be easier if you had a simple guide on using it.
also possibly a sheet and instructions to enter one's latitude, longitude, and the current year.

is it possible to assign the current system time as a variable and the HA and positions are then recalculated when refreshed?
that way position info would be realtime or accurate when refreshed.

[Andrew C]

Hi Alistair,

Many thanks for the comments. I am certainly happy to put some time into preparing a guide if there are some people like yourself who think they could make use of it, either for their own personal use or for sessions with friends or the public.

Having put the formulas into spreadsheet form, the core calculation part is now easy to modify - I have flagged the three places where that is needed on the first sheet in red - LAT, LONG and DISPLAY TIME (UT).

However, the charting step in Excel is a manual one, so it would be up to people to generate the charts for their location and time and add whatever labels they wish to enhance the readability of the chart.

In my case for example the constellation lines and boundaries are mostly a nuisance on a chart, but there are some (such as the Taurus triangle, the false cross in Carina/Vela, Crux, the Sagittarius 'teapot' and the Orion 'saucepan') that are instantly recognisable and are helpful both to me and people less familiar with the night sky. This part is very much a matter of personal preference.

When it comes down to it, I suspect (or at least hope) there is a category of astronomy buff who like me is familiar with spreadsheets, though not in the league of designing and programming a fully fledged star application, but happy to spend the time creating and customising a set of easily readable charts for their location and set of 'interesting objects'.

I do have another version of the spreadsheet that calculates the ALT AZ for any member or pair of members in my table of objects in real time just by plugging in the object numbers should that be of interest for other purposes (such as calculating separation angles), but my main purpose in starting the thread here was to see what interest there is in the charting option.

Cheers,

Andrew

[alistairsam]

Hi Andrew,

that second spreadsheet you mentioned would also be very good.
what I was looking for was to get a list of objects that are say above a certain magnitude of brightness and are visible after dark in a certain location at a date and time.

alt/az co-ordinates would be useful for users with dobsonian mounts and manual setting circles on the Dob mounts as we could then look at the list, look it up in stellarium or your second chart for its current alt/az position and try and point the dob to that location.
eg, I was in the snake valley camp night before last, had some dark skies, but was'nt sure at what i could see at that time even though I had stellarium, so a chart/list from a spreadsheet like yours would have been very useful.

[Andrew C]

Hi again Alistair,

I have modified and attached the second spreadsheet tonight to allow the LAT and LONG and TIMEZONE to be changed at will, so that you can try it out. It was previously loaded with my local data as absolute values so I had to make some adjustments.

The way to use it is to open the 'interesting objects' sheet, set your LAT and LONG (replacing the Alice Springs ones in red in rows 2 & 3), and read off the row number for one or two objects of interest (e.g. beta centauri is 129). Then switch to the 'alt az calculation' sheet, and plug in the row numbers for the object(s) inthe blue cell(s) in rows 17 (& 60). Then set your CURRENT TIMEZONE in red in row 25. The date and current local time are both automatic, but you can change the date manually if you want to calculate for other than the current day. Make sure your computer is showing the correct local time to match these settings by the way.

You should then be able to read off the true ALT and true AZ from rows 47/58 and 88/99. If you subsequently hit the F9 key these will recalculate each time.

The 'angular difference' sheet shows the sky separation angle between the two objects.

Once LAT, LONG and TIMEZONE are set, you only need to change the object numbers for new object calculations.

You can add your own objects to the list to customise it.

Please let me know how it goes.

Cheers

Andrew

[alistairsam]

Hi Andrew,

thanks again. appreciate the effort. what I was looking for was a list of objects that can be viewed for a particular date/time from a location, and their magnitudes. that way, I can draw up a list of objects for an observing session for a night.

is it possible to add the alt/az colums next to the objects, and by refreshing, it recalculates co-ordinates of all the objects relative to current LST rather than choosing one at a time.

your formulae look quite complex, but I'll play around with it a bit as well.

is it possible to combine objects from the major catalogs and filter them between the Dec ranges -90 to +30 for our hemisphere if I'm correct.

[Andrew C]

Hi Alistair,

I think for that you would need to customise the first spreadsheet workbook.

You will see towards the right side of the INT(ERESTING) OBJ(ECTS) sheet in this workbook a series of columns CR through DJ whose formulae are used to determine those objects in the full list that are visible in each quadrant and overhead at the nominated time and place (in the demo 9.30pm January 15th in Alice Springs). e.g. TUC47 is visible in the south at ALT 31, AZ 199.

If you were to change the LAT and LONG to Melbourne
(say -38/145) and the DISPLAY TIME UT to 11.00 (which = 22.00 EDST) on the LSTCALC sheet, TUC47 changes to ALT 45, AZ 202. You will also notice that some of the entries in the south display jan column (such as NGC 6397 at row 183) have changed from 0 to 1, indicating that this object is now visible where it wasn't before. Conversely, others have disappeared from view, such as NGC1316/1317 at row 33. In fact this latter one has disappeared upwards, and is now visible in the adjacent zenith column and chart.

For clarity in the demo, I had removed the formulae from the alt and az columns DA & DB for objects that are not visible or 'active' in the south at that time and place (and similarly for the other quadrants) but they are easily reintroduced by copying the az and alt formulae from an active object above or below (don't copy across).

If you are not interested in generating the charts, you can also change the formulae for example so that all quadrants are included in the one set of columns. If you look e.g. at the south SCP entry (cell CZ2) you will see that I am only setting this entry to active ("1") if the altitude is between 0 and 70 degrees, and the az is between 135 (southeast) and 225 (southwest). You could remove the az test altogether, and change the alt to accept the range 0-90, or say 20-90 if you want to exclude objects that are close to the horizon.

Note that e.g January 15th at a particular time is nearly equivalent to December 15th at the same time plus 2 hours, so you can use the chart for any date by adjusting the time. The columns AN to CP take account of the 'nearly' which I use for the other months charts, but you could skip worrying about using those if you are not looking for a precise altitude and azimuth.

For magnitudes you could add a further column, and introduce a magnitude test into the formula as well if you want to show only those above a certain brightness.

Cheers,

Andrew

[ballaratdragons]

Andrew,

I appreciate your effort, and thank you, but when I went to open your link I had to click on too many things for my liking.

I am not computer savvy and when I get asked to participate in a Microsoft survey thingy just to get into your maps that's when I gave up.

Can't you just attach them as images like everyone else does, or link to somewhere I don't have to get involved in some Microsoft thing?

[Andrew C]

Sorry Ken,

I had to convert the file to a zip file since it was too big to upload otherwise because of the (sensible) Ice In Space file size limits. This may have had consequences for you if you are not running the standard Microsoft stuff. Others may be able to shed some light on this. I don't know why you have been asked to do a Microsoft survey, but usually such requests can simply be closed off with no ill effects.

Anyway, I'll send you an unzipped copy by email - I have your address from your message to me the other day about the A2333. You'll still need the Excel program on your computer to open it though.

I didn't think there was a lot of point in just uploading the charts as images, because the examples in the demo are unique to my particular location and time, and the spreadsheet files and Excel program and some changes are needed to generate versions that present the object positions as they would appear somewhere else.

You would need a level of knowledge of the Excel spreadsheet program/application to be able to generate charts for your location, and we haven't gone down that track yet - so far, I have been responding to Alistair's request, which in effect is taking my basic idea and object location data and generating something other than sky charts.

Cheers, Andrew

[ballaratdragons]

Thanks Andrew, I appreciate the effort to get them to me :thumbsup: