BSIA 2021 February AstroNotes

Notes on what to see from the light polluted skies of Baker Street and elsewhere!

Sun and the Moon.

The Sun is waking up from its minimal activity reached in 2019. Last year there were 208 days (57%) when the Sun was spotless compared to 77% of spotless days in 2019. To date this year there has been less than half of January days without a sunspot to see, so it is worth getting out solar telescopes and white filtered binoculars to view the Sun’s disc during any breaks of sunshine. I use the website to see the sunspot sizes, names and numbers on the disc on any one day. Several Irregulars have imaged sunspots recently, posting on our Facebook page – I’m looking forward to there being more solar activity in the months to come as I continue to hope we may be allowed to meet for my annual solar observing picnic on SUNday, 20 June. The British Astronomical Association has a good primer on solar observing on their website

I enjoy observing the Moon at 1st Quarter, a phase when beautiful craters are various sizes and formations can be seen close to the straight terminator with binoculars and small telescopes. 1st Quarter in February falls on the 19th when I can guarantee clear skies (!). Again, please post images and sketches to our social media pages with accompanying notes for other Irregulars to enjoy and comment upon. The last time we met at the Hub was at our annual MoOnday lunar gazing event, in March 2020. Maybe we will be allowed to congregate again this year for another such event – a Monday (moOnday, get it?) coinciding with the lunar 1st Quarter is on 13 September. Fingers crossed for MoOnday2021!


If you haven’t seen the Ice giant Uranus before, early February gives you the last opportunity to bag it before it reappears in our dark skies next Autumn. It must be said the planet looks small (3.6 arcseconds in apparent diameter) and featureless through small telescopes;  using my 3” refractor I bring to the Hub it is little more than a tiny pale blue disc. But it is three billion kilometres away from us, sunlight reflected from its cloud tops takes 165 minutes to reach your eyes. On 1st February it sets just after midnight so around that date look in the south-west at about 8pm (20:00UT) when it will be at a high altitude of 41 degrees. Numerous smartphone apps can indicate its and other celestial objects’ exact positions throughout the year. I use SkySafari Pro to indicate the altitude and azimuth of any object at any time so I can dial these values into my cheap manual AltAz mount, the one I bring to the Hub.

Mercury is a tough find this month, it’s very low in the west, not particularly bright, only visible for the first week before it disappears behind the Sun (inferior conjunction occurs on the 8th). A better time to observe Mercury will be on the 6th March when it will be in the morning sky- more next month.

Venus is too close to the Sun this month, it’s a morning ‘star’ very low down and only visible for a few minutes before sunrise early in the Month. 

As Mars is appearing dimmer through the first half of the year, observe early in the month if the clouds allow. On the 1st the red planet sets at 1.27am so will be also seen in the south-west in the evenings above Uranus – bag both planets during one observing session! Mars is visible with the naked eye, on the first its visual magnitude is  +0.5 dimming to +1.0 by month end and its apparent size shrinking from 7.8 to 6.3 arcseconds throughout February as the planet races away from us. By the end of February Mars will be very close to the Pleiades – a chance for a great photo op.

Jupiter and Saturn are not at their best this month. Both are very low in the south east, close to the Sun and only visible for a few minutes before sunrise. I shall not bother trying this month.

The ice giant Neptune, the furthest planet, is in the south-west at sunset but only at 9 degrees elevation when it’s dark at 7pm on the 1st. Maybe worthwhile looking for it if you have an unimpeded view of the horizon at that time. It’s dim (magnitude +7.9 so a ‘scope is needed) and tiny in apparent size (2.2 arcsec). Best to wait until September when it’s brighter, bigger and at opposition.

Deep Sky Objects – those outside the solar system.

In February the constellation of Gemini is overhead in dark skies. The heavenly twins, Castor and Pollux are the two brightest stars of this zodiacal group. They are high in the sky (70 deg)  due south at 11pm at the beginning of February. Castor is above its twin and is a double star that can be ‘split’ by a small telescope, both components separated in the field of view. Cassini first discovered the dual nature of Castor in 1678, the first gravitationally bound objects observed beyond our solar system. Modern astronomers have shown Castor to be a complex aggregation of six suns in three binary groups, all orbiting each other! Although known as Alpha Geminorum it is not brighter than its twin, Pollux or Beta Gem. Perhaps each has changed its luminosity since they were named four centuries ago. Pollux is also a double star, its dimmer secondary is far too faint to be seen with most ‘scopes employed at our meetings. Physically the Twins are not alike: Castor sextuplet is made up of hot bluish-white stars and dim red dwarfs while Pollux is a ‘cool’ yellow-orange giant, approx. nine times the diameter of our Sun and with a current luminosity of 46 suns. It is closer to Earth, 34 light years away whereas star-light takes 51 years to reach us from Castor. You are seeing Castor as it was in 1970! 

Let us know what other objects you hope to observe in February.

Other notes.

A common question posed by adult beginners in our group is ‘What is the best telescope to buy to start stargazing?’ Irregular David Arditti answers this question here In the article there is a picture of David at one of our Hub meetings. We hope to see David and many other Irregulars back at the Hub before too long!

Keep warm when observing in February nights. Keep safe and keep looking up!

Eric, for the Unofficial Force of the Baker Street Irregular Astronomers