Shaped like a pinwheel due to its anticlockwise rotation over many millions of years, the Pinwheel galaxy is an enormous collection of stars nearly twice the size of our own galaxy, the Milky Way. It is also known as M101, being one of the last entries in Charles Messier’s catalogue after it was discovered by Pierre Méchain in 1781.
Like the Milky Way, it is a spiral galaxy. The most notable features of such galaxies are the graceful spiral arms that arc out of the centre. We can see them because we view this galaxy face-on, unlike other galaxies which are seen at other angles from the Earth.
The shape of the spiral arms is similar to the cloud formations in hurricanes or typhoons and can be described mathematically with the shape of the logarithmic spiral. This is often found in nature, such as mollusk shells.
The galaxy contains newborn stars as well as globular clusters containing stars that are many thousands of millions of years old. It is located in the constellation Ursa Major (the Great Bear). Use the pair of stars Dubhe and Merak (the pointers) to find the faint pole star (Polaris) and the position of north.
M101 is situated at a distance of 21 million light years from Earth. This means that the light we are seeing in the accompanying image left the Pinwheel galaxy about 21 million years ago – many millions of years before humans ever walked the Earth. It can be faintly glimpsed with binoculars from a dark site, but since its light is spread over a large area it can be difficult to spot even using a telescope if there is light pollution. Spring is the best time to see it as it will be highest in the sky.
As the month progresses, summer constellations Cygnus (the Swan), Aquila (the Eagle) and Lyra (the Lyre) make their appearance in the east, with bright star Vega heading the ‘summer triangle’ asterism. The Milky Way also starts being seen from dark locations devoid of light pollution.
Close to the Pinwheel galaxy in the night sky, Venus dominates the evening skies in the west soon after sunset, even as we approach the summer solstice on June 21. The June night sky shows the summer constellations rising in the evening and the winter constellations heading down very early into the western twilight.
The bright planet Jupiter is now low in the west and joins Venus close by at the end of the month when they will be very close to each other on June 30 and July 1. Venus shines brilliantly as it approaches the Earth so these two very bright worlds, the king and queen of planets, are hard to miss, unless it’s cloudy. As mentioned, they already appear in the evening sky and they will be drawing closer together each evening throughout June.
Saturn, having late last month already had its closest approach to the Earth this year, still shines brightly as well, low in the south. This is a good time to see Saturn and maybe try to see its largest moon, Titan, through binoculars.
Mars, having been conspicuous earlier this year, has now moved around the sun such that in mid-June it will be ‘behind’ it, as seen from the Earth, and thus it will not be visible in the coming weeks.
Astronomical events in June
Tomorrow at 9.02pm: Moon close to the planet Saturn (evening sky)
Tuesday at 5.19pm: Full moon
June 9 at 4.42pm: Last quarter moon
June 10 at 5.39am: Moon perigee (at its closest to the Earth) 369,700km
June 16 at 3.05pm: New moon
June 20 at 12.28pm: Moon close to the planet Venus (evening sky)
June 21 at 5.38pm: Summer solstice
June 21 at 8.10pm: Moon close to the bright star Regulus (evening sky)
June 23 at 6.01pm: Moon apogee (at its farthest from the Earth) 404,100 km
June 24 at 12.03pm: First quarter moon
June 26 at 3.58am: Moon close to the bright star Spica (morning sky)
June 29 at 2.27am: Moon close to the planet Saturn (morning sky)
June 30 at 3.18am: Venus close to the planet Jupiter (evening sky)
Alexei Pace is president of the Astronomical Society of Malta.