When to see Venus and the full moon
KShortly after sunset a bright star appears over the western horizon: it is the Venus, our neighboring planet in the solar system. This spring it is developing into the undisputed “evening star”. Because it orbits the Sun within Earth’s orbit, we never see it very far from our home star – it appears either early in the morning before sunrise or, as now, at dusk. Its bright light – which is, of course, nothing more than reflected sunlight – is partly due to its relative proximity (about 150 million kilometers separate us from Venus in late April), partly due to its highly reflective atmosphere. Venus is surrounded by a dense layer of clouds, which reflects around two-thirds of the sunlight it receives back into space. For comparison: With our earth moon, this degree of reflection is only twelve percent on average.
As Venus is currently approaching Earth, its perceived brightness will increase very slightly over the course of the month. It will reach its peak splendor in mid-July, but as the sun sets in, 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 means 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 stands roughly in line between them. It comes close to the “Seven Stars”, i.e. the Pleiades, up to 2.5 degrees, which corresponds to about the thickness of an outstretched thumb.
The Pleiades represent seven sisters in ancient Greek mythology, so Venus will join them for a few days. This makes for a nice photo opportunity, especially with the Hyades further east and the bright star Aldebaran: the best time is an hour after sunset, around 9:30 p.m. If you look closely, you may be able to see a faint, slightly yellowish star just above the horizon and a little to the right: This is Mercury, which also has its best evening visibility of the year at the beginning of April. As the innermost planet of solar system Mercury moves even less away from the sun and is thus 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 Leo 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 home 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, couldn’t 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 shines twenty thousand times the sunlight into space. We can still see them very clearly from their distance of 260 light-years.
Arktur is different: at a distance of 37 light years, it is the closest of the three. Only 1.5 times as massive as the Sun, it still has two hundred times the luminosity of the Sun, because Arcturus has expanded to twenty-five times the Sun’s radius – it is an old giant star at the end of its life cycle. Its huge surface shines brightly – and at around 4000 degrees it is quite cool and therefore reddish. Its reddish color can be seen with the naked eye, especially when compared to the whitish Regulus and Spika.
Falling star stream Lyrids between April 14th and 30th
April is also the month of the Lyrid falling star stream. These fragments of a comet discovered in 1861 flare up between April 14 and 30 and appear to originate in the sky near the Lyra constellation, found deep to the northeast on the chart. The maximum of the Lyrids this year falls on the morning of April 23, and thus conveniently close to the new moon. It is best to wait until the constellation Lyra has climbed higher above the horizon, which is around midnight. Then the star scale fireworks begin, but a rather inconspicuous meteor shower.
Although there were exceptional years, as a rule (and very likely also in 2023), the zenith hour rate, i.e. the number of the maximum Lyrid meteors visible per hour under ideal circumstances, is around 20. The zenith hour rate is the number of meteors that can be seen under perfect could count in a dark sky if the radiant (in this case the radiant point in the lyre) was 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 the zenith and one cannot see the entire sky anyway, the true hourly rate, i.e. the number of meteors actually visible per hour, is well below the zenith hourly rate ten or less.
Full moon on April 6th
Sun: April 1, sunrise 8:03 am, sunset 8:57 pm; April 30, sunrise 7:04 am, sunset 9:42 pm.
Moon: April 6, 7:35 a.m.: full moon; April 13, 12:11 p.m.: last quarter; April 20, 7:13 am: new moon; April 28, 12:20 am: first quarter.