Martin presents the Sky this Month
Report by Martin Male
For those who don’t know us, Jane & I host observing evenings at Old Romney, where you are most welcome. Please apply via the website and Mike will put you on the list.
The Sun
The Spring Equinox is on Thursday 20th March. The Sun will then be above the horizon more than 12 hours per day. The clocks go forward on Saturday 30th March, making astronomy at reasonable hours more difficult. Solar Maximum of the 11-year sunspot cycle is expected around now, but to date it has proved to be at its least active for a century with relatively few sunspots to date. However, it would be a brave person who says its over just yet, as solar cycles are far from regular in length and activity.
If you have not yet had a look at the Sun with the 90mm Coronado telescope, do get along to one of the Flamsteed sessions run at the ROG. Even if there are no spots visible there is always much to see on the surface of our nearest star.
The Moon
New Moon 1st, First Quarter 8th, Full Moon 16th, Last Quarter 24th, New Moon 30th.
The second of two full moons in a calendar month is called a “Blue Moon”, though I don’t know if there is an equivalent nickname for 2nd New Moon. Anybody know of such a name?
Planets: Mercury
May possibly be observable mid month just before dawn if you have a clear Eastern horizon, but this will be difficult to see.
Venus
Low in the East at dawn. Brilliant at magnitude -4.5 . The Moon is close to Venus on the morning of 27th March, so a good photo opportunity. With a telescope you’ll be able to see the phase of Venus growing to “half moon” by months end.
Mars
Mars is in Virgo and at the start of the month is just less than 6 degrees to the left of the bright star Spica. Mars will be at opposition on April 8th, when it will be at its closest to us since January 2012. Oppositions of Mars occur at about two year two month intervals, as we have to play “catch up” from our orbit. Mars is red–orange in appearance, and rises around 22:00 at the start of the month and about two hours earlier at month’s end. Its brightness increases dramatically during the month from magnitude +0.5 to -1.3 with its angular size increasing from 11.6 to 15.2 arc seconds at opposition next month. Given good conditions and a modest telescope, it is possible to see features on Mars’ surface such as the polar caps and dark green/black markings.
The orbit of Mars is markedly more eccentric (that is non circular) than Earths, so given the combination of these eccentricities, at opposition Mars can appear between 13 to 25 arc seconds in size. The opposition in 2003 was the most favourable for 60,000 years, though it will be almost as big in 2018. For comparison, the Moon & Sun at 0.5° angular size are about 1,500 arc seconds, Jupiter is about 40 arc seconds.
Mars has an axial tilt very similar to Earth (25 to 24° respectively) and has seasons like Earth. The North Polar Region is currently tilted towards us by ~19 degrees so the North Polar Cap is particularly prominent. The Polar Cap will shrink as the summer season progresses for Mars’ northern hemisphere; this shrinkage will be visible through quite modest telescopes. Mars has a very thin atmosphere, about 100th the density of Earth’s. An unwelcome feature of the atmosphere is possibility of dust storms arising during “summer” on Mars that can obscure the surface features of the planet. There were dust storms in 2001 & 2007 that obscured the surface features for a month or so – bad news if you’ve been waiting two years to get the best views!
The dark surface features of Mars change over time as a result of dust deposition, where wind blown dust can obscure or reveal the darker underlying surface. It’s easy to understand how astronomers, before close up observation by space probes, believed that these changes may have been due to seasonal growth & die back of vegetation.
Jupiter
Still very prominent in the evening sky and well placed throughout March for observation, Jupiter is very bright at magnitude -2.3 and is 40 arc seconds in size. There are numerous events such as eclipses and transits of Jupiter’s four Galilean moons, so do a “Google” search or use a planetarium programme to seek out their timings.
Saturn
Rising around 2300 mid-month, it will be at its highest around 0300 at magnitude +0.4. The rings are quite spectacular, currently angled at around 20°. The planet is around 20 arc seconds in size and the rings around 40 arc seconds. Titan, the largest of Saturn’s moons can be found with binoculars. It is distinctly orange in colour and it’s interesting to follow its nightly change in position as it orbits the planet.
Saturn will not get very high in the sky in 2014 for northern viewers, and indeed it will be less well placed for a few years to come as it moves from Libra through Scorpius & Sagittarius.
Uranus & Neptune
Too close to the Sun for observation this month.
Meteors
No regular showers of note this month, but sporadic meteors always occur.
Comets
No comets readily visible in small telescopes this month
And finally…… Constellation of the month: Leo
Well placed in the evening sky in spring, Leo will be visible in the South East. This Zodiac constellation looks a little like its name, which is more than can be said for most of them! The Sun will be close to Regulus, the brightest star in Leo in early August. Gamma Leo is a nice double star visible in small telescopes. Denebola “tail of the Lion” in Arabic marks the hindquarters of our celestial feline. The backward facing question mark has Regulus at its base. This star at mag +1.35 is 77 light years distant with a surface temperature of 12700°K and is blue white in colour.
Stars vary from dull red at low temperature to blue white at high temp, just like a fire in a grate. For comparison the sun is 5770°K. Barnards star, a close red dwarf has a surface temperature of 3100°K. Although it is “only” six light years away it is very dim at mag +10. Indeed there are no red dwarfs visible to the unaided eye although they are the most numerous star type; about 70% of all stars are Red Dwarfs, so its sobering to think of that when we look at the night sky I think.