U Orionis is one of our long-period variables, with a usual range of 6.3 – 12.0. It is due to reach maximum brightness in April/May, but observations by Don Matthews show U Orionis is increasing in brightness and may become visible in binoculars over the course of this month. Orion will remain visible, low in the west, for the next few weeks, so hopefully there will be some opportunities for visual observers to see this star before Orion disappears behind the Sun.
Below is a light curve, produced by Don Matthews, which shows the past behaviour of U Orionis.
R Leonis, in the constellation of Leo the lion, reaches maximum this month.
R Leonis, a long-period variable, easily found near the bright star Regulus will reach maximum brightness this month. Like all long period variables, R Leonis is a red giant star and the variations in brightness are due to pulsations in the star’s outer layers.
R Leonis has an extreme range of 4.8 – 11.0, but a more usual range is 5.4 – 10.5. The exact behaviour of the star is never the same from one cycle of variation to the next. R Leonis is currently visible in binoculars and it will be interesting to see just how bright it becomes over the next few weeks.
Below is a light curve produced by Tracie Haywood showing the behaviour of R Leonis last year.
Weather permitting, astronomers in the UK can start the new year by observing both RZ Cassiopeiae and U Cephei on the same night.
There will be two eclipses visible from the UK on the evening of January 1st 2019. RZ Cassiopeiae will be in mid-eclipse at the start of the evening, mid-eclipse is at 17:30 UT, so you can watch RZ Cassiopeia brighten as the evening progresses. The duration of a RZ Cassiopeiae eclipse is almost five hours.
U Cephei will be in mid-eclipse at around 23:00 UT, so you can watch the eclipse over the course of the night, if it stays clear. The duration of an U Cephei eclipse is around nine hours.
These two light curves, produced by Tracie Heywood will give you some idea of what to expect.
For observers in the UK, the 14th of November will be an opportunity to observe two eclipsing variable stars in one night. RZ Cassiopeiae will be in mid-eclipse at approximately 22:00 UT; as will Beta Persei.
The duration of RZ Cassiopeiae’s eclipse is approximately five hours and the duration of Beta Persei’s eclipse is nine and a half hours. You can start observing these stars as soon as it gets dark; using the charts on the SPA’s website. Try and make estimates every half-hour and report any observations you make to the SPA VSS.
Three of the long-period variables (LPV) on the sections observing program are now visible in binoculars. T UMa, S UMa and Chi Cygni (Mira) are now all visible in binoculars.
All three stars are typical LPV and show a variation of several magnitudes over the course of several hundred days. For most of their period they are two faint to be seen in anything other a large telescope. So, this is a good opportunity for binocular users to make some useful observations.
All LPV are cool, red giant stars in the later stages of their life. These stars can be thought of as consisting of two parts; a high density core surrounded by a low density outer layer. Shock waves emanating from deep within the star’s interior, coupled with the star’s low surface gravity, means that these stars can pulsate. It is these pulsations, these variations in the star’s radius, that cause the star’s variation in brightness.
In about five billion years from now, our own Sun will become a red giant star. It’s something to consider, that when observing these stars, you are looking at the Sun’s future.
Over the last month several members have been kind enough to send in their variable star observations. I’ve received observations from Bob Steele, David Buehler, Don Matthews, Jonathan Shanklin and Tracie Heywood. All member’s observations will be published in the annual VSS report next March. In the meantime, here are a couple of light curves sent in by Tracie Heywood.
Over the course of October, several of the long-period variables in our program will be on the rise. Omicron Ceti (Mira) and Chi Cygni are rising and due to reach maximum in December. While T Ursa Majoris and S Ursa Majoris are also expected to rise and reach maximum in November. Both Mira and Chi Cygni have the potential to reach naked eye visibility; but Chi Cygni will be low in the west by December and may be tricky for some people to obverse. When at maximum, T Ursa Majoris and S Ursa Majoris will reach about the seventh magnitude; so should be easily seen in binoculars. Of course with long-period variables, it is impossible to say exactly when they will reach maximum and how bright they’ll be, each cycle of variation is unique. However, it’s the uncertainty in the behaviour of long-period variables that makes them so interesting to observe.
There is also a couple of opportunities to observe Beta Persei (Algol) and RZ Cassiopeiae in October. For the night owls among you, RZ Cassiopeiae will be in mid-eclipse on the evenings of the 22nd and 27th of October, at 00:00 UT and 23:30 UT respectively. Algol will also be in mid-eclipse on the evening of the 22nd at 23:50 UT.
The charts for all of these stars are available on the website.
As we move into autumn, the nights are rapidly getting longer and darker, which means for many, the observing season starts anew. This makes September the perfect time for adding new variable stars to your observing program.
Despite the fact that it’s autumn, it is still possible to observer many of the summer constellations still visible in the west. Although Hercules is often regarded as a summer constellation it won’t be setting until after midnight and is therefore well placed for observing in the early evening sky.
Even under moderately light polluted skies the ‘keystone’ of Hercules is easy to find below Vega and once it is identified you can use it to locate two variable stars suitable for binoculars: G Herculis and UW Herculis.
For more information about these stars follow this link: this link
After spending the summer close to minimum, both Chi Cygni and Omicron Ceti (Mira) are on the rise. Both stars are expected to reach maximum brightness in early December. At their faintest, both stars are only visible in large telescopes, but over the course of the next couple of months they should be observable in binoculars. At maximum brightness, both stars can be seen with the naked eye from a dark site. Chi Ceti has a typical maximum brightness of around the fifth magnitude, while Mira usually reaches the third magnitude, so both stars should be visible in binoculars, even from a light polluted site.
Looking to the north-east the eclipsing binaries RZ Cas and Beta Per (Algol) are visible. There will be a favourable eclipse of RZ Cas on the 20th; with a mid-eclipse time of approximately 22:00 UT. Each eclipse lasts five hours; so the eclipse should be well underway by the time it gets dark. RZ Cas varies between magnitudes 6.4 and 7.8, so its variation can be followed with a modest pair of binoculars. There are no favourable eclipses of Algol in September.
If you want to try and observe any of these stars, the charts are on the website.