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See Earth-crossing asteroid Icarus in closest approach for 75 years

By Ade Ashford

Posted on 15 June 2015 by Ade Ashford

At 4:39 pm BST on 16th June, a historically interesting near-Earth asteroid named Icarus will dash by our planet at a distance of just five million miles, or 21 times the Earth-Moon distance. Discovered on 27th June 1949 by Walter Baade at Palomar Observatory, just a few months after the legendary 200-inch Hale Telescope saw first light, this one-kilometre-wide space rock received the provisional designation 1949 MA. Once the particulars of its 409-day orbit had been determined, astronomers quickly realised that it was an unusual object.

Earth-crossing asteroid 1566 Icarus (1949 MA) will miss our planet by a safe five million miles, or 21 lunar distances, at 4:39 pm BST on 16th June 2015 — the closest it will approach Earth until 2090. Click the graphic to open an interactive Java applet. Image credit: NASA JPL Small-Body Database Browser/Osamu Ajiki/Ron Baalke/Ade Ashford.

1949 MA has a decidedly elliptical orbit that causes it to approach the Sun to within ⅔rds of the perihelion distance of planet Mercury before swinging out to aphelion beyond the orbit of Mars some 204 days later. Appropriately, 1949 MA was therefore named after Icarus of Greek mythology who flew too close to the Sun. For over half a century it held the distinction of being the asteroid that passes closest to the Sun until 2000 BD₁₉ was discovered in 2000. Icarus was also the first asteroid to be observed with radar during its close approach of June 1968.

Mile-wide asteroid 1566 Icarus’ encounter with Earth during June 2015 is the nearest it gets to our planet until 2090, but there is no fear of a collision. Icarus makes its closest approach to us at 4:39 pm BST on 16th June at a distance of five million miles (eight million kilometres), or 21 times the Earth-Moon distance. The viewing window for UK-based observers is ~16th—22nd June when the asteroid is moving at a average speed of ½°/hour against the background stars. Icarus reaches a maximum brightness of magnitude +13.5 on the 19th when it will be in the constellation of Boötes near Arcturus, the brightest star in the northern celestial hemisphere. The tick marks show the position of Icarus at 12 am BST on the dates shown. Click on the chart for a printable full-size version. AN illustration by Ade Ashford.

Classified as an Apollo asteroid, 1566 Icarus has an orbital resonance with Earth that causes it to make close approaches to our planet in the month of June at intervals of nine, 19 and 28 years, but never close enough to pose a threat of collision. The flyby of June 16th — 5,004,000 miles (8,053,000 kilometres) or 0.05383 astronomical units — is the nearest occurring between the years 1968 and 2090 (for comparison, the last close approach of 1996 was 9.4 million miles, or 39 times the Earth-Moon distance). Fortunately for observers in the British Isles, Icarus will be well placed for observation for this apparition and will reach magnitude +13.5 as it speeds across the northern night sky.

When to observe 1566 Icarus
Weather permitting, this fascinating asteroid will be bright enough to be observable from the British Isles from 16th—22nd June and we will not have to contend with moonlight. However, twilight around the Summer Solstice will be an issue — particularly for those in the north of England and Scotland. Generally speaking, the window of opportunity is between midnight and 2 am when the sky will be dark enough over the UK, but try to view as close to 1 am as you can (all times quoted in this article are British Summer Time, BST).

The phase angle, illumination and distance of Icarus will change rapidly over the week that it is observable, hence its visual magnitude will vary from approximately +14.8 on 16th June, to a peak of +13.5 on the 19th, back to around +14.1 on the 22nd. From 18th—20th June, users of 8-inch and larger telescopes can see Icarus moving against the background stars, something that you will perceive in real time as the asteroid averages 0.5°/hour during the period in question. Owners of smaller telescopes on accurately driven mounts may wish to photograph it or use astrovideo methods to capture it.

First night: June 16th, 12 am—2 am
Icarus will be faint tonight at magnitude +14.8 and only seen visually in 12-inch telescopes and larger, but very easy to locate as it traverses the bowl of the Big Dipper in Ursa Major, passing just 1.4° north-northeast of β Ursae Majoris, or Merak — the lower of the two pointer stars to the Pole Star, Polaris — around 12:20 am BST.

Over the following week we will provide a nightly guide to what to expect, but for those with computerised GoTo telescope mounts or instruments equipped with digital setting circles, the following table gives astrometric Epoch 2000.0 coordinates computed for an observer located in the centre of the British Isles. Parallax will be therefore be negligible for the whole of the UK.