About Star Pointer
What Is It?
Welcome to Star Pointer, the site that tells you where to point your
telescope for any Messier, Caldwell, or Herschel 400 object that is currently
visible. In addition, it can present a collection of double stars that make
good targets for small telescopes. Star Pointer displays a page like the page
segment shown above. It presents visible all targets in a chosen catalog that
are currently at an elevation of 25 deg or more. You'll need a telescope with
setting circles, like the capable Orion
09007 SpaceProbe 130ST Equatorial Reflector Telescope. Or, you can take your simple Altazimuth telescope
and add setting circles, as illustrated on the Pipe Fitting Tripod.
Star Pointer is
a handy observing utility, especially for your next Star Party, as it
gives you ready access to multiple star-object catalogs on your Smart
With a bit of luck and a well aligned telescope, it lets you dispense with charts,
at least when looking at objects contained in any of the selectable catalogs.
How Do You Use it
To use the utility, simply select the catalog and type of coordinate frame
you wish to see, and the current list and position of all visible items in the
selected catalog will be listed for your current observing location.. The
objects are listed in azimuth order, starting with the Southwest. That way
setting objects that might drop off of the chart are shown first, and moving
from item to item causes the least telescope movement.
Even if you use a telescope that already has a computer driven mount,
the Star Pointer utility is handy because it shows at a glance what's
currently up for any of the selected target lists. I use it to select
targets when using my Celestron NexStar 5 SE Telescope. First, it lists what
is visible, and if I enter them into my NexStar hand controller in the
order shown, the telescope can move from object to object quickly, as they
are in azimuth order.
The utility displays on a plain black screen with red lettering so as to
have the least impact on your night vision. Not fancy, but hopefully
more useful that way. Messier and Caldwell objects are listed just by their
catalog sequence numbers. At least some computer driven telescopes, like my
have both the Messier and Caldwell lists in their memory, and entering just
the respective list's target number is sufficient. But at least for my
NexStar, the Herschel 400 list is not specifically included, though all of the
objects are by other names. That's why the Herschel 400 list includes the
Herschel 400 sequence number, and each object's Messier or NGC id.
Location Is Necessary
The utility does need to know your Latitude and Longitude in order to make
the necessary object position calculations. If coordinates are entered
manually, they are saved in year-long cookies so that the next time you use the
utility on the same computer or device, it will already know your observing
location. You can select the Enter Lat/Lon button at any time to enter
new coordinates. You can enter either degrees, like 45.52, or
hours:minutes:seconds, like 45:30:10. The displayed position is always
Star Pointer's Location Method Sequence:
If no Cookies, use Geolocation if user allows it. *
If error on Geolocation or not allowed, ask user, then save in cookies.
* - Note, if your device doesn't have GPS, it's probably better to
block auto-geolocation and enter a manual value. It avoids Google's
geolocation routines, which often aren't that accurate anyway.
Works For Both Alt/Az And Equatorial Mounts
If using an Altazimuth mount, just select your desired catalog and begin
picking objects. Point your leveled and North-aligned telescope to the
indicated coordinates and enjoy. North aligned for an altazimuth mount
basically means that the azimuth setting circle reads zero when pointing at
Polaris. If not in the telescope FOV, the object should be just outside of the
FOV. A little searching may be required, depending upon the accuracy of your
alignment. When ready for the next object, just select it from the displayed
list, as the object coordinates are automatically updated about every 30
seconds or so.
If using an Equatorial mounted telescope, first use the Init
button to see a list of calibration stars. Find one that is visible, point
your North-aligned telescope at it, and position your setting circles to
read the values displayed for that star. Right Ascension is displayed in
hours:minutes:seconds format, and Declination is displayed in Degrees, which
is most convenient for most small telescopes. Once you've set your
telescope setting circles as per the Init table, proceed to selecting
targets of your choice for telescope pointing coordinates.
I've found that some users can't easily adjust their telescope's Right
Ascension indicator. For those users, the Init selection provides
another option. You can point your telescope to one of the listed guide stars,
and insteading of trying to adjust your Right Ascension indicater to match
the chosen star, you can select the Set RA Reading button that is
This allows you to select the index of the selected start (0 thru 10), and then enter your Right Ascension indicators reading. Enter it in
hours-colon-minutes, like 13:25. The app will then calculate a bias between
the proper reading and your telescope's RA reading. It will add this bias
to the displayed Right Ascension values for each presented object.
Note that when listing RA/DEC coordinates, the Right Ascension values
are biased values, not static star chart values. That is, the Right Ascension
values are adjusted to reflect the amount of Earth rotation since the
Init button was pressed. This allows you to set your RA setting circle
only once, and from that time on you can point your telescope by the recently
updated coordinate list and be pointed at or near the object of your choice.
If you have trouble, be sure that your location is entered properly. Also
note that the computer time must be correct for the Altazimuth coordinates,
but is less important for the RA/DEC coordinates. What's important with the
RA/DEC coordinates is to set your setting circles to the right position
according to the guide star that you pick, and that you do that shortly after
using the Init button.
Hopefully the periodically updated star lists will work for you, though
I cannot guarantee that they will. I've used the results of the equations
in other forms however, and have had good luck with them.
Use Star Pointer as an Observing Planner
While the original intent of the utility was to give real-time pointing
coordinates for favorite star targets, by using the Time Bias feature,
one can force the utility to advance the time so you can see what might be up
later in the evening. For example, say it's only 4 in the afternoon and you
want to see what objects will be observable at 9 in the evening (21:00). You
can select the Set TmBias button and then select 5 to bias the
local time by 5 hours. That way the charts will be presented for a time 5 hours
from your current time, letting you see what's up around your expected viewing
Just remember to reset the time bias back to zero when trying to use the
coordinates real time. It always defalts to a time bias of zero when started,
so you'll generally be just fine.
If the positions listed by Star Pointer don't seem to be accurate, there's a
few things you can check.
First, is your location correct? It's listed under the
control buttons. If it's not correct, you can select the Enter Lat/Lon
button and re-enter it.
Next, is your computer time correct? If you're using Equatorial coordinates, then
the computer time isn't important, but it's very important for Altazimuth
Finally, is your telescope properly aligned?
For equatorial mounts, the polar axis must be aligned with Polaris (for
Northern Hemisphere observers). Be sure to use the Init EQ Mount list of
alignment stars to pick one, and set your setting circles to the reference star
values. This only needs to be done at the beginning of your observing session.
For Altazimuth mounts, the vertical axis must be plumb (or the base level). Also,
the azimuth setting circle should read zero when pointing at Polaris.