Located some 30 million light years away, the Sombrero galaxy contains around 800 million stars. It appears to host, at its centre, a supermassive black hole about a billion times the size of our sun. This is around 250 times the black hole in the centre of our own galaxy, the Milky Way.
Elsewhere in the sky, this is the best month in which to observe the smallest and most elusive of our solar system’s planets, Mercury, named after the Roman deity, the messenger to the gods.
Since Mercury, like Venus, orbits the sun within the Earth’s orbit, it can appear in the Earth’s sky in the morning or the evening, but not in the middle of the night. Although Mercury can appear as a bright object when viewed from Earth, its proximity to the sun makes it more difficult to see against the twilight glow.
Enter Venus, shining brighter than any other star in the evening sky. From its position high in the west, Venus directs us to Mercury, a dimmer planet on its lower right, in the direction where twilight appears brighter. Mercuty started appearing in the west-northwest in evening twilight on April 28 and will continue till May 12.
Mercury lies farthest from the sun on May 7, so it reaches its peak appearance and climbs highest in the twilight sky. It appears about 11 degrees above the horizon 45 minutes after sunset. Mercury remains near the altitude from today until May 9. Further down on the horizon is Mars, but this is even fainter than Mercury and thus very difficult to see during this period.
Mercury has the most eccentric orbit of all the planets with its distance from the sun ranging from 46 to 70 million kilometres. Its orbit is inclined by seven degrees to the plane of Earth’s orbit. This is why we can observe transits of Mercury across the face of the sun only 13 times a century. The next Mercury transit will occur on May 9, 2016.
Its closeness to the sun makes Mercury a very challenging planet to visit. Between 1974 and 1975, NASA’s Mariner 10 (the first spacecraft to use the gravitational ‘slingshot’ effect and the first NASA mission to visit multiple planets) flew by Mercury three times and mapped less than half of the planet’s surface.
The second NASA spacecraft to visit Mercury was Messenger, which was launched from Cape Canaveral Air Force Station on August 3, 2004. However it was not until March 17, 2011, that Messenger started orbiting Mercury. Scientists regard this probe’s mission as a great success as it has provided priceless data about the planet and has helped answer a lot of questions. Among the most important discoveries was that of finding frozen water so close to the sun.
Thanks to Messenger we also know that Mercury used to be bigger and that over the past four-and-a-half billion years it has shrank by over seven kilometres in radius. Messenger has given scientists reams of data to be analysed. Unfortunately last Thursday, after running out of fuel, the probe created its own crater on Mercury when it crashed on the planet.
Astronomical events in May
Tomorrow
Full moon at 4.42am.
Tuesday
Aquarid shower maximum at 1.36pm.
Moon close to Saturn at 5.18pm.
May 11
Last quarter moon at 11.36am.
May 15
Moon perigee (366,000km) at 1.23am.
May 18
New moon at 5.13am.
May 23
Saturn opposition (brightest) at 1.53am.
May 25
First quarter moon at 6.19am.
May 26
Moon apogee (404,200km) at 11.12pm.
Alexei Pace is president of the Astronomical Society of Malta.