A monthly look at astronomical events in the sky and on Earth
Best seen at the beginning of the month (first quarter on the 2nd) through to around the 6th, then again from a wafer-thin crescent low in the SW on the 25th through to the end of the month. As a waxing crescent, it passes some degrees below and to the left of Venus on the 27th.
This elusive planet puts in two equally favourable evening appearances this year. The first is between the 5th and 15th of February; the second is in late May. What is interesting about Mercury is that it is the fastest moving planet in the solar system, and as a result moves towards then away from us very quickly. It whips round the sun at such a speed that you have to be on your toes to catch a glimpse of the little blighter! There are two conditions that affect our ability to see Mercury. The first is its altitude above the horizon at sunset; the second is its magnitude. If its altitude is too low at sunset, then by the time the sunset sky glow has reduced in brightness, the planet is too near the horizon and we can’t see it through the murk. If its magnitude isn’t high enough, it’s not bright enough to spot against a bright after-sunset sky. Here are the figures for this month’s apparition. Don’t forget the magnitude scale runs from negative (bright) to positive (less bright) and also that a change in magnitude of 1.0 indicates a change in brightness of about 2.5.
|Date (Feb.)||Alt. at Sunset (Degrees)||Magnitude|
You will clearly see there is a conflict. Mercury’s maximum brightness (Mag. -0.9) doesn’t correspond with its maximum altitude (14.2°). So it’s a matter of compromise, and the optimum viewing dates are between the 9th and 12th.
To spot Mercury, get out there just before sunset and note where the sun goes down, wait about half an hour then look at a point in the sky about 3° to the left and 10° above where the sun set. Mercury is there. This situation applies at about 5:35pm on those optimum viewing dates. If you do get a telescope on to Mercury, you’ll see it as an 8 arc second diameter 32% illuminated crescent on the 13th/14th.
Venus dominates the south-western sky this month. On 1st February, the planet will be at 28° altitude at sunset and at magnitude -4.1. By the end of the month it’s at 36° altitude and magnitude -4.3. As mentioned above, the crescent Moon passes it on the 27th. Venus is still showing as a gibbous disc 17 arc seconds in diameter, and it will continue to brighten as it catches up with the Earth. Greatest eastern elongation is reached in late March, when Venus sets nearly five hours after the Sun.
Mars, Jupiter and Saturn
Mars is only visible low in the SSE in the morning sky and it’s only 5 arc seconds in diameter. Wait until nearer its opposition in October.
Both Jupiter and Saturn are also morning objects but too close to the sun and too low in the sky to be worth observing.
Uranus is still observable from about 7 pm until 10 pm, when it approaches the western horizon. Please see November 2019’s What’s Up for more information and a finder chart.
Neptune is too close to the Sun to observe.
Non-Solar System Objects
These are best seen when the Moon is out of the way, and that’s from the 12th until the end of the month.
If you haven’t paid them a visit this winter, then the objects listed in December’s What’s Up and January What’s Up are worthy of your attention, but I’d like to encourage you to take a look at one of the most amazing objects in the night sky. It’s only visible with a telescope but even a small one will do. It’s the Crab Nebula.
The Crab Nebula (Messier M1)
In 1758, Charles Messier, following the predictions of Edmund Halley that a bright comet would reappear in the constellation of Taurus, spotted a fuzzy object near Zeta Tauri. He soon realised however that the object wasn’t moving so could not be a comet. That triggered him to begin listing all the objects in the sky that could be mistaken for comets. That list is the now the famous “Messier Catalogue” and that first object in it he designated as M1.
We now know that M1 is the remnant of a supernova explosion, recoded by Chinese astronomers in 1054. It was four times brighter than Venus and visible in daylight for 23 days, and remained visible at night for two years but then faded from view.
The Crab is now at magnitude 8.4 and about 7 x 5 arc minutes in size. It’s easy to find as it’s close by Zeta Tauri (the star at the end of the Bull’s lower horn). The sky chart below shows its exact position.
The Crab doesn’t jump out at you, but it’s definitely worth a look. Ensure the sky background is really dark (no moon or wispy high cloud) and try it with different magnifications to find the best one for you and your telescope. I also advise you have a read of these two related articles. They include some remarkable images, notably the amazingly detailed HST image taken in 1999/2000.
Wikipedia entry, The Crab Nebula
Wikipedia entry SN1054 (describing the supernova that created the Crab).
Do please give it a try. To see with your own eyes the aftermath of that gigantic explosion can be thought-provoking. And you can then say, “I’ve seen that. Did you realise that some of the stuff you and I are made of can only have come from exploding stars like that”. That’s got to lend you an ear or two at dinner parties!
Open cluster M35
A fine half-degree diameter fifth magnitude open cluster. Look out for the much smaller and tighter NGC2158 cluster, of magnitude 8.6 (similar magnitude to the Crab) to its lower right.
The Rosette Nebula
You’ve probably heard of the Rosette Nebula but may not know where it is or whether you could see it. Its correct designation is NGC2237 but at its centre is NGC2244 which can be spotted (position shown on chart above) as a 4.8 magnitude,24 arc minute diameter open cluster. The much larger 1° diameter Rosette nebula is only visible against the clearest and darkest sky background, but it’s worth having a go whilst you’re in that part of the sky. Use binoculars or a low power and make sure you’re completely dark-adapted. The red colour however only comes out in photographs.
Passes of the International Space Station (ISS)
The ISS is visible on many occasions in February. See the Heavens-Above web site for more details. Here is a link with all fields relevant to York selected.
It’s “all go” in the satellite and spacecraft world at the moment. For up-to-date news, scroll https://www.space.com/32286-space-calendar.html
Clear skies and good viewing.
John Rowland 29/01/2020