A personal blog by George Gladfelter

Occultations

03/02/2019

Occultations for March

**
All dates and times are MST
Elevation above the horizon (and azimuth) in degrees.**

**
Events when the object is below the horizon,
or the Sun is not, are omitted.**

**Occultation of Saturn 03/01/2019
09:11 to 13:41:32 not visible in N.A.**

**Occultation of Saturn 03/28/2019
21:59:19.5 to 03/29/2019 00:18:54.1**

**not visible from North America**

**Occultations in March of stars
brighter than 5.5 magnitude and visible from S. Dakota: None.**

Notes about occultations:
The timing is very specific to your
exact location. Few clocks can be relied on to be accurate at the
sub-second level, including the inexpensive radio-controlled clocks which are
typically corrected once per day around midnight, and the clock display on a
computer or phone (the correction process typically runs infrequently).
The accuracy of a clock can be verified by time signals broadcast on shortwave
frequencies, or by using a GPS receiver, or by accessing a network time server
on the Internet if you have software specifically designed for this purpose.
However, it is very
difficult to visually determine the exact time when a star appears or disappears
at the illuminated limb of the moon. Photography, therefore, is very
helpful. No lunar occultations of __a bright star__ will be visible this year
from Rapid City.

Note that at the time the angle center-of-object to center-of-Earth to center-of-Moon is minimal, the center of the Moon's shadow normally strikes the surface of the Earth at a specific location. That location is listed as "Mid-occultation observing point". If the center line misses the surface of our planet, the location listed is where the observer on the surface of Earth should be in order to be closest to the center line of the shadow.

If you need data for your particular location, please send me an email with the latitude, longitude, and preferably also your altitude above mean sea level in meters or feet, for your observing location. Please specify the units you use, such as degrees and meters and specify North or South, East or West for your coordinates.

High Precision Daily Polynomial Coefficients for Lunar Coordinates

02/17/2019

The Astronomical Almanac lists the apparent right ascension, apparent declination, and true distance (light time not factored in) of the moon at zero hours Terrestrial Time for each day of the year. The online web site at http://asa.usno.navy.mil/SecD/LunarPoly.html gives daily polynomials for apparent right ascension, apparent declination, and horizontal parallax for any desired time during the day listed. However, there are a few points to consider: (1) the polynomials for 2019 are not yet posted as of February 15th. (2) The coefficients for horizontal parallax do not have the required number of significant figures to match the distance information listed in the Astronomical Almanac. (3) The daily polynomials are never given for years beyond the current year.

Posted here is a text file for 2019-2020 giving the daily coefficients for R.A., Dec., Dist., and H.P. The distance is the true distance in kilometers (light time not factored in). The others are in degrees. Each quantity is to be computed as:

quantity = A_{0} + A_{1}f
+ A_{2}f^{2} + ... + A_{5}f^{5}

where f = h/24, with h = time in hours **(TT)**

and 0.0 <= f < 1.0

The results for the angular coordinates should agree very closely with the apparent coordinates in the Astronomical Almanac, section D, and the distance should agree within a few meters.

If you have any questions, comments, or needs concerning these polynomials, please send me an email.

My email address: g e o r g e 0 7 @ r a p . m i d c o . n e t (omit the spaces).