Epsilon Lyrae

The small constellation of Lyra hides many celestial treasures. Almost every one of its stars is interesting. But the star Epsilon has long been considered one of the most amazing pearls of visual telescopic astronomy, and every amateur astronomer, even with a small telescope, has certainly looked at Epsilon Lyrae, and did so at the first opportunity. And there is something to see here.

Let's start with the fact that Lyra is a summer constellation. In the middle latitudes of the northern hemisphere, it does not set below the horizon (at least at the latitude of Moscow, the main star of the constellation, Vega, is visible all year round). But the best time to observe the stars of Lyra is summer and autumn.

The Summer Triangle figure formed by the stars Vega, Deneb and Altair

Vega, together with the brightest stars of the constellations Cygnus and Aquila, forms the famous asterism, the “Summer Triangle” (sometimes called the “Summer-Autumn Triangle”), which is located in the widest part of the summer Milky Way. Lyra lies just on the edge of this dimly glowing band, in which the radiance of millions of distant stars has merged.

Among the stars of the Lyra constellation, composed of relatively faint luminaries, Epsilon is the closest to Vega. Thanks to this, it is quite easy to find in the sky. Find Vega – you will find Epsilon.

The figure of the constellation Lyra, and the location of the star Epsilon in it

This star has not preserved its own ancient name, and perhaps never had one. Other equally faint stars of Lyra mostly have some names, mostly Arabic. But the heroine of our story did not get a name. Although, among English-speaking astronomy enthusiasts, there is a nickname for it – “Double Double”.

Vega and the star Epsilon Lyrae - at low magnification — Vega and the star Epsilon Lyrae – at low magnification

For most people who can see Epsilon Lyrae with just their eyes, the star seems like an ordinary faint star. Its visible brightness does not exceed 4.5 stellar magnitude – it is not easy to see it in the city at all. Its position in the sky saves the situation – in the summer, Epsilon Lyrae climbs almost to the very zenith, and there the light pollution is minimal. But even with the lightest optics – binoculars or a telescope – it is easy to notice that this star consists of two fainter luminaries, at first glance, as if identical.

Strictly speaking, the most experienced observers are able to notice the duality of Epsilon Lyrae simply by eye – under ideal conditions. After all, the angular distance between the components is 3.5 arc minutes, and this is close to the limit of the resolution of the ideal eye (which ophthalmologists determine to be 2 arc minutes… although no ophthalmologist has ever successfully passed such a test for 2-minute resolution of two faint stars).

But if you have a telescope, even a small one, at medium magnification (60-80s) you can see that each of those two Epsilons also exhibits duality. True, much closer.

This is why the star got its nickname “Double Double”. But more often it is simply called “quadruple” or simply “Multiple Epsilon”.

The star Epsilon Lyrae divided into four components - two close star pairs, widely separated from each other. View through a telescope at medium magnification — The star Epsilon Lyrae divided into four components – two close star pairs, widely separated from each other. View through a telescope at medium magnification

Each of these star pairs is so close that it was once used as a test object to check the quality of telescopes. If the instrument clearly showed the duality of both components of Epsilon Lyrae (Epsilon One, the one to the north, and Epsilon Two, the one to the south), such a telescope was considered to be of very high quality indeed. Now, of course, this applies only to amateur telescopes.

I remember that the Small School Refractor (lens diameter 60 mm, magnification 60x) produced by the Zagorsk Instrument-Making Plant since the mid-1950s could not separate Epsilon Lyrae into 4 components (at best, into three). But the Large School Refractor (80 mm and 80x) could, if it was well adjusted at the plant.

The era of school refractors was replaced by reflectors (mirror telescopes) of the Novosibirsk Instrument-making Plant – “Alcor” and “Mitsar”. And the small (65 mm), but mirror “Alcor” already showed all 4 components of Epsilon Lyrae perfectly. And “Mitsar” – even more so. At the same time, the adjustment of the optics of both telescopes was easily carried out at home.

And now it is believed that Epsilon Lyrae is a fairly easy multiple star to resolve – there are more difficult ones. And this is simply a classic – a beautiful and easy star system with which amateurs who have just bought a telescope begin their explorations.

But I remember how incredibly beautiful these 4 stars looked in the 6-inch Zeiss of the Moscow Planetarium Observatory – at the lowest available magnification – only 56 times. No strain of vision, no special techniques were required to see this system of four stars in all its grandeur.

The star Epsilon Lyrae divided into 4 components - two close star pairs, far apart. View through a telescope at high magnification — The star Epsilon Lyrae divided into 4 components – two close star pairs, far apart. View through a telescope at high magnification

What are these stars?

Each of the members of this star quartet is comparable to Sirius. Sirius is close to us — only eight and a half light years from the Earth and the Sun. But the 4-fold Epsilon Lyrae system is much further — almost 20 times. The average distance to this star quartet is estimated at 160 light years.

Of course, this was not immediately clear. Most of the time, astronomers were not sure of the stable gravitational connection between the two stellar pairs of Epsilon Lyrae. But with the increasing accuracy of measuring stellar parallaxes, it was possible to find out that both pairs are at almost the same distance from us and are approaching us equally quickly – at a speed of about 30 kilometers per second. But this speed is relative. And most likely, it is caused by the fact that it is the Solar System that is flying in the direction of the constellations Lyra and Cygnus. The personal contribution of the stars of the Epsilon Lyrae system to our rapid approach is small.

It has not yet been possible to determine exactly how much time each pair of stars in the Epsilon Lyrae system needs to complete a full orbital revolution. There are only typical estimates, according to which the period can be quite long – from 300 thousand years and even up to half a million. Although for stars this is not so much.

And how small, tight pairs rotate in this system – this was measured, because the movement there is more intense and noticeable.

Astronomers now know that the Epsilon-1 pair, which is more northern and closer (in appearance), makes one revolution around the common center of mass in 1800 years. Epsilon-2, which is more southern and seemingly wider (the stars are visually located further from each other), rotates much faster – in 800 years. Why is this? – because we see not the full radius of the orbit, but its inclined projection onto the plane of vision.

The distances in these pairs of stars are quite surmountable for civilizations of our level of development – 100-150 astronomical units – approximately the same distance that the Voyager 1 and Voyager 2 spacecrafts, as well as their predecessors, Pioneer 10 and Pioneer 11, have already flown.

But the distance between these pairs is enormous – about 1/7 of a light year. This is quite enough for the stars to hold each other in their gravitational field, but excessive for chemical rockets, which would be able to deliver a souvenir from the inhabitants of the Epsilon-1 system to the inhabitants of the Epsilon-2 system only in thousands of years.

But in the sky of each of these civilizations there will shine a beautiful double star, brighter than our planet Venus in its best visibility conditions, only not one, but two of them, and separated by a distance slightly greater than the diameter of the lunar disk.

In 1984, using the speckle interferometry method, the presence of another star in the Epsilon-2 system was revealed. In two subsequent experiments, this was confirmed, but not definitively. A small shadow of suspicion of errors and interference still exists. According to the results of these measurements, the supposed distance of the 5th star in the Epsilon Lyrae system from the closest component may be about 0.2 arc seconds, which is extremely small for direct optical observation, but still somewhere on the edge. And the large telescopes with adaptive optics under construction may or may not see this star directly, and then the question will also be resolved.

But at the same time, in recent years, scientists have discovered five dwarf stars in the vicinity of Epsilon Lyrae, which are most likely gravitationally connected to the well-known and clearly visible in amateur telescopes four. They are currently being closely watched and their motion features are being studied. And if all suspicions are confirmed, the 4-fold Epsilon Lyrae system could become a 10-fold star system, which would be more correctly called an open star cluster. And all this will most likely be found out in the very near future.

And now, while the weather is warm and clear, it’s time to point the telescope at the constellation Lyra, find the star designated by the Greek letter Epsilon, and see how things are going for them – the inhabitants of the “World of Four Suns”.

Fantastic World of Four Suns. Perhaps this is how the four stars of the Epsilon Lyrae system are seen from one of the planets that have not yet been discovered there (but it is not excluded). Drawing made using a neural network

A quarter of a century ago I dedicated to the constellation Lyra music albumin which one play It is precisely about the star Epsilon Lyrae – it is called “Multiple Epsilon”.

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