Shortly after sunset, a bright star appears above the western horizon: it is Venus, our neighboring planet in the solar system. This spring, it is developing into the undisputed "evening star". Because it orbits the Sun within the Earth's orbit, we never see it very far away from our host star – it appears either early in the morning before sunrise or, as now, at dusk. Its bright light – which, of course, is nothing more than reflected sunlight – is partly due to its relative proximity (about 150 million kilometers separate us from Venus at the end of April), and in part to its highly reflective atmosphere. Venus is enveloped by a dense layer of clouds that reflects about two-thirds of the received sunlight back into space. For comparison: In our Earth's moon, this reflectance is on average only twelve percent.

As Venus is currently approaching Earth, its perceived brightness increases quite slightly over the course of the month. It will reach its greatest glow in mid-July, but as it sinks into the sun's glow, the best time to admire Venus in the sky this year is now!

Mercury achieves best evening visibility in early April

In Earth's sky, Venus moves through a very interesting region known as the "Golden Gate of the Ecliptic." This refers to the area between the star clusters of the Pleiades and the Hyades in the constellation Taurus: Venus passes the two clusters in the middle of the month; on April 12, it is roughly on a line between them. It comes close to the "seven stars", i.e. the Pleiades, up to 2.5 degrees, which corresponds approximately to the thickness of an outstretched thumb.

The Pleiades represent seven sisters in ancient Greek mythology, so Venus joins them for a few days. This makes for a nice photo opportunity, especially together with the further eastern Hyades and the bright star Aldebaran: The best time is one hour after sunset, around 21.30 pm. If you look closely, you may be able to see a faint, slightly yellowish starlet just above the horizon and slightly offset to the right: This is Mercury, which also reaches its best evening visibility of the year at the beginning of April. As the innermost planet of the solar system, Mercury moves even less away from the Sun and is therefore even more difficult to see than Venus.

Spring constellations dominate the sky

After dusk, the spring constellations dominate the sky. Just to the south we find the lion with its main star Regulus. The whitish star is "only" 80 light years away from us, but shines 300 times brighter than the Sun: this makes it one of the brightest stars in the sky; our host star, on the other hand, could only be seen from this distance with optical aids. The other two corners of the Spring Triangle, Spika in Virgo and Arcturus in Bearkeeper, could not be more different. Spika is a young, hot and therefore enormously luminous giant star: ten times heavier and eight times larger than the Sun, it radiates twenty thousand times the sunlight into space. We can still see them very clearly from their distance of 260 light years.

Arcturus is different: at 37 light-years away, it is the closest of the three. Only 1.5 times as heavy as the Sun, it still has two hundred times the Sun's luminosity, because Arcturus has inflated to twenty-five times the Sun's radius – it is an old giant star at the end of its life cycle. Its huge surface glows brightly – and with around 4000 degrees quite cool and thus reddish. Its reddish color can be seen with the naked eye, especially compared to the whitish Regulus and Spika.

Shooting star stream Lyrids between 14 and 30 April

April is also the month of the shooting star stream of the Lyrids. These fragments of a comet discovered in 1861 light up between April 14 and 30 and appear to originate in the sky from near the constellation Lyra, which we find on the map deep in the northeast. The maximum of the Lyrids falls this year on the morning of April 23, and thus conveniently near new moon. It is best to wait until the constellation Lyra has climbed higher above the horizon, which is the case around midnight. Then the starscale fireworks begin, a rather inconspicuous meteor shower.

Although there have been exceptional years, as a rule (and very likely also in 2023) the zenith hour rate, i.e. the maximum number of Lyrid meteors visible per hour under ideal circumstances, is around 20. The zenith hour rate is the number of meteors that could be counted under perfectly dark skies if the radiant (in this case the radiating point in the lyre) were exactly at the zenith, i.e. above our heads. However, since the sky is always more or less artificially brightened, the radiant is usually not at its zenith and you cannot see the entire sky anyway, the true hour rate, i.e. the number of meteors actually visible per hour, is clearly below the zenith hour rate, perhaps ten or less.

Full moon on April 6

Sun: April 1, sunrise 8.03 am, sunset 20.57 pm; April 30, sunrise 7:04 a.m., sunset 21:42 p.m.

Moon: April 6, 7:35 a.m.: Full moon; April 13, 12:11 p.m.: last quarter; April 20, 07:13 a.m.: New moon; 28 April, 0.20 a.m.: first quarter.