PROJECT DAPPER (Dedicated Amplitude and Period of Polaris Elementary Research) will monitor the variability of what we in the northern hemisphere normally refer to as “the North Star”. The correct astronomical designation is Alpha Ursae Minoris, also known as Polaris. It's the brightest star in the constellation the Little Dipper (the Lesser Bear), in contrast to the Big Dipper (the Greater Bear). The variability of Polaris was discovered by Enjar Hertzsprung in 1911.

To the naked eye, Polaris looks as constant in position and brightness as Shakespeare noted in “Julius Caesar”…

“I am as constant as the norther star
of whose true-fixed and resting quality
there is no fellow in the firmament...”

Polaris sits very close to the North Celestial Pole, which means that the entire night sky seems to rotate around it if the viewer is in the northern hemisphere. The southern sky has no "pole star" as such.

Under close scrutiny, Polaris turns out to be a classical Cepheid variable. Cepheid-type variable stars are hardly rare, but Polaris shows some unusual characteristics.

Polaris stands out from other Cepheid variable stars because of its erratic behavior. Before the early 1960’s the amplitude of its variability was over 0.1 magnitude and was steadily decreasing. In the mid 1960’s the amplitude very rapidly decreased to 0.05 magnitude. Since that time the amplitude has changed in an inconsistent manner. In 2008 an article in The Astronomical Journal indicated that the amplitude is increasing again.

The period of variability also seems to be slowly increasing. It’s now just shy of four days.

While the above is curious enough, an article in Science (2004) points out that Polaris is one magnitude brighter then when Ptolemy observed it sometime around 150 CE. If so, most theories of stellar evolution can be thrown out, as such a dramatic change in magnitude in such a short period can’t be explained by current ideas.

Polaris is also a multiple stellar system. The largest component, the one we can see with the naked eye, is Polaris Aa. Polaris B, the second largest of the trio, and finally Polaris Ab.


The goal of DAPPER is to provide The American Association of Variable Star Observers (AAVSO) with accurate analysis of the amplitude and variability of Polaris. Observations of Polaris are lacking, it's been over a year (as of this writing, 30 December 2018) since any observations of Polaris have been submitted to the AAVSO.

The AAVSO is the clearinghouse of variable star observations in the U.S. and for a large part of the world. The AAVSO then makes the data available to other researchers.


PROJECT DAPPER will use NIMROD (North star Imaging and Magnitude Recording Optical Device) to observe Polaris on every night that weather permits. NIMROD uses a cooled CMOS camera imaging through a Johnson-Cousins V-band filter through a 400mm focal length f/8 lens. NIMROD is dedicated to Project DAPPER and for the foreseeable future with have no other targets.

Images will be vetted for photometric suitability, dark subtracted, flat-fielded and analyzed with MPO Canopus software. Results will be passed to the AAVSO and published on this web site.

NIMROD is complete. Observations should have begun in mid-January 2019, however mother nature hasn't seen to cooperate, and it's been cloudy since January 6th. Hopefully March will bring some clear sky.

NOTE: The acronym NIMROD was inspired by another NIMROD project, the National Intesive Meteorolotical Research on Downbursts, also known as the Northern Illinois Meteorological Research on Downbursts. The author shares an equal passion for astronomy and meteorology.

Back to the top

Questions/comments, E-mail me at john at theastroimager dot com