April Night Sky 2018

Article by: Yanina Metodieva, PhD student at the Armagh Observatory and Planetarium

March has certainly been an eventful month, and now we’re in to April. The Spring has definitely sprung and we’re enjoying the stretch in the evenings, even if it makes stargazing a little trickier. Sure we have to go out later and later at night, but as long as we still have a flask of hot chocolate with us we’re fine.

The Romans called this month Aprilis, which may derive from the verb aperire meaning “to open”, referring to flowers and fruits opening. April is the cruellest month or so says TS Elliot in the poem “The Waste Land,” but we beg to differ! We think April is great and we would like to share with you what is great in the April night sky.

On April 16th we will not see the moon in the sky, as it will be a new moon. This would be the best time to get the telescopes out and do a bit of stargazing, as there will be no moonlight in the sky to hinder your view. So what should you look out for?

Leo the Lion

The constellation of Leo the Lion will be prominent in the night sky, and the brightest star in this fierce constellation is called Regulus. Before I go into any detail about the star Regulus I would like to make a connection to pop-culture here. In the night sky we have the star Regulus, and the star Sirius (the Dog Star) will have just about gone below the horizon. If we look to the ever popular fiction books of Harry Potter, we can see where JK Rowling go some of her inspiration from. Sirius Black is Harry Potter’s godfather and in the book he is known for transforming into a giant black dog. Sirius the Dog star is found in the constellation of Canis Major, the Great Dog! In the book Sirius Black has a brother and his brother is called, none other than, Regulus! In the story Regulus does not transform into a lion or anything like that, however he is a bad guy that ends up turning good and sacrificing himself for the greater good. Some would say he had the heart of a lion.

Anyway I have digressed enough, the star Regulus is considered a blue-white “B” star that lies on the main sequence of stellar evolution. Like the sun, Regulus fuses hydrogen to helium in its centre, but it is more massive than the sun and therefore hotter and brighter.

Lurking nearby and unseen by the naked eye are two very faint companions to the much larger bright star. The binary pair (two dwarfs, orange and red) are about 4,200 AU away from Regulus. If you would like to see this particular star, make sure you look south on 16th April, and to make it even better, use your telescope for a better view.

Cancer The Crab

Sticking with our signs of the zodiac, another constellation in the sky during this time is Cancer the Crab. This constellation is the faintest of the zodiac signs and would be great for more advanced stargazers to spot. The brightest star in the constellation is Al Tarf, Beta Cancri. It is approximately 290 light years from earth, and has a visual apparent magnitude of +3.5. Its absolute magnitude is −1.2. Al Tarf is an orange K-type giant, about 61 times the radius of the Sun.

Turning your heads East in the evenings, you can spot the orange star Arcturus. This is the brightest star in the constellation Bootes The Heardsman, and the fourth brighest star in the night sky. Arcturus is an orange giant star, 133 times more luminous than our own Sun, but much farther away, about 37 light years away.

A few interesting events will occur this April – a double conjunction of Mars and Saturn with the Moon, and the Lyrid meteor shower.

In the first days of April, the planets Mars and Saturn will appear very close together in the night sky. Rising together around 3am, they will be separated by only 1 degree on the night of 2nd April. A few days later, on the 7th and 8th April, the waning Moon will join the party, forming a triangle with the two planets, separated around 4 degrees away from one another. Visible close to the Milky way, the trio will be very attractive for observations and astrophotography.

The Lyrid meteor shower is the first strong shower for this spring. The radiant of the Lyrids lies in the constellation Lyra, which means that the meteors will seem to shoot out of the constellation Lyra. The meteor shower will be active in the period 14-30 April, with a maximum on April 22nd 18:00 GMT. The Lyrids this year will have little moonlight interference from the waxing crescent Moon, and in good weather conditions you can see about 18-20 white meteors per hour. Occasionally the Lyrids have stronger maximum with up to 90 meteors per hour.

Another interesting event for this month is the launching of the TESS mission. Tess stands for Transiting Exoplanet Survey Satellite, and it’s a mission designed to look for Earth-sized planets around other stars. TESS will be launched on board a SpaceX Falcon 9 rocket and it is scheduled for 16th April this year.