Night Sky Almanac 2023: A stargazer’s guide

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It is useful to know some of the special terms for various parts of the sky. As seen by an observer, half of the celestial sphere is invisible, below the horizon. The point directly overhead is known as the zenith, and this point is shown on the monthly charts for several different latitudes, where it is an important reference point. The (invisible) point below one’s feet is the nadir. The line running from the north point on the horizon, up through the zenith and then down to the south point is the meridian. This is an important invisible line in the sky, because objects are highest in the sky, and thus easiest to see, when they cross the meridian in the south. Objects are said to transit, when they cross this line in the sky. Castor and Pollux in Gemini are near the zenith for observers at 30°N, but for most northern observers the constellation is best seen when facing south. The head of Draco is now higher in the sky and easier to recognize, with its long, straggling ‘body’ curling round Ursa Minor and the Pole. Ursa Major has begun to swing round towards the north, and Cassiopeia is now lower in the western sky.

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In this photograph, the narrow lunar crescent (about two days old) has been over-exposed to show the Earthshine illuminating on the other portion of the Moon, where the dark maria are faintly visible.

The Stars

Mercury is close to the Sun. It passed superior conjunction on March 17, and comes to greatest eastern elongation (19.5° from the Sun, at mag. -0.0) on April 11. Venus is very bright (mag. -4.0 to -4.2) in the evening sky. Mars (mag. 1.1 to 1.3) moves across Gemini over the month. Jupiter is lost in the twilight in Pisces. Saturn (mag. 1.0.) is in Aquarius, very low in the morning twilight. Uranus (mag. 5.8 to 5.9) is slowly moving eastwards in Aries. Neptune is still in Pisces, at mag. 8.0 to 7.9.

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Similarly, the date given for an event is the date as it applies at the Greenwich meridian, i.e., in UT. Occasionally, this may differ from the date as given by your local time. An event that occurs (say) late in the night in Europe may seem to occur on the previous day to an observer to the west (such as in the USA), when local time is taken into account. This is another complication that is avoided by using the Universal Time standard. Learn more about the full Moons of August, how they got their name, and best days by the Moon in our August Moon Guide. But even this idea proved inadequate to describe the motion of the planets, so the concept of the deferent was added. In this the circular motion of the epicycle was carried round the Earth on a circle that was itself not centred on the Earth, but offset from its centre. Most of the brightest stars have names officially recognized by the International Astronomical Union. A list of these, with their Bayer designations and magnitudes, is given here. At 21:54 on the evening of 28 February 2021, a brilliant fireball (a bolide) was observed over Gloucestershire. Observations allowed the orbit of the parent body to be determined, showing that the body’s original location was the outer region of the asteroid belt between Mars and Jupiter.

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The southern sky is dominated by Orion, visible from nearly everywhere in the world and prominent during the northern winter months. For observers near the equator it is, of course, high above near the zenith. Orion is highly distinctive, with a line of three stars that form the ‘Belt’. To most observers, the bright star Betelgeuse (α Orionis), shows a reddish tinge, in contrast to the brilliant bluish-white Rigel (β Orionis). The three stars of the belt lie directly south of the celestial equator. A vertical line of three ‘stars’ forms the ‘Sword’ that hangs south of the Belt. With good viewing, the central ‘star’ appears as a hazy spot, even to the naked eye, and is actually the Orion Nebula (M42). Binoculars reveal the four stars of the Trapezium, which illuminate the nebula. Both the planets Mars and Uranus end their retrograde motion in January 2023 and revert to direct motion. An image of Ceres, obtained by the Dawn spacecraft on 4 May 2015 from a distance of 13,641 km. Ceres comes to opposition on 21 March 2023. The southern meteor shower, the π-Puppids, begins in April. This shower starts to be active on April 15, two days after Last Quarter and lasts until April 28, one day after First Quarter, with maximum on the night of April 23–24 when the Moon is a waxing crescent. The shower was unknown until 1972. The rate seems to be variable, reaching a maximum of about 40 meteors per hour in 1977 and 1983. It is difficult to predict how many meteors will be seen. As with the Lyrids, maximum occurs just after New Moon. The parent comet is believed to be Comet 26P/Grigg–Skjellerup. Eta Carinae (η Carinae) is one of the most massive and luminous stars known. It is estimated to have a mass between 120 and 150 times that of the Sun, and be between four and five million times as luminous.

2023 Night Sky Almanac: A Month-by-Month Guide to North

Farther south, the Milky Way runs diagonally across the sky, and the constellation of Vela straddles the meridian. Slightly farther south is the constellation of Carina, with, to the west, brilliant Canopus (α Carinae), which lies below the constellation of Puppis, which is itself between Vela and Canis Major in the west.

For a precise view from your location, visit the free online planetarium Stellarium. Enter your location and the date of the event to see a replica of the sky where you live.