Guide to U Orionis

A Mira type variable, near the Taurus/Gemini border, that currently reaches maximum brightness in the mid spring. Gaps occur in the light curve each year from May to August when U Ori is not observable in the might sky

A 2-year light curve for U Orionis

U Orionis is a red giant star. Its brightness variations are primarily due to pulsations in the star’s outer layers that not only cause the star to expand and contract, but which also lead to corresponding changes in its surface temperature.

The surface temperature changes also allow simple molecules to form as the surface cools and then disassociate when it warms again – and these also affect the star’s brightness – it doesn’t rise and fall in brightness at a constant rate.

Extreme brightness range 5.3 – 12.6
More typical range 6.3 – 12.0
Period of variation 372 days ( a week longer than a year)
Frequency of observation Worth checking a few times per month
Observe using 50mm binoculars will suffice for most of the time, but 50-80mm binoculars will be needed to cover the middle of its range. A telescope will be required to follow it all the way down to minimum
Visibility Can be observed from mid August to early May
Dates of maxima late April 2017, early May 2018, mid May 2019

The two charts which follow show the location of U Orionis.

The first shows the wider area around U Orionis – note that it is well north of the main pattern of Orion.

U Ori
Chart for U Ori

The second shows the binocular view. You can follow the changes in U Orionis by comparing its brightness with that of the lettered comparison stars.

U Ori
Chart for U Ori