On the right of Aldebaran, in the position indicated in Plate 1, Map I., are the stars [zeta] and [beta] Tauri. If with a low power the observer sweep from [zeta] towards [beta], he will soon find—not far from [zeta] (at a distance of about one-sixth of the distance separating [beta] from [zeta]), the celebrated Crab nebula, known as 1 M. This was the first nebula discovered by Messier, and its discovery led to the formation of his catalogue of 103 nebulae. In a small telescope this object appears as a nebulous light of oval form, no traces being seen of the wisps and sprays of light presented in Lord Rosse’s well known picture of the nebula.
Here I shall conclude the labours of our first half-hour among the stars, noticing that the examination of Plate 1 will show what other constellations besides those here considered are well situated for observation at this season. It will be remarked that many constellations well seen in the third half-hour (Chapter IV.) are favourably seen in the first also, and vice versa. For instance, the constellation Ursa Major well-placed towards the north-east in the first quarter of the year, is equally well-placed towards the north-west in the third, and similarly of the constellation Cassiopeia. The same relation connects the second and fourth quarters of the year.
[Illustration: PLATE III.]
A HALF-HOUR WITH LYRA, HERCULES, CORVUS, CRATER, ETC.
The observations now to be commenced are supposed to take place during the second quarter of the year,—at ten o’clock on the 20th of April, or at nine on the 5th of May, or at eight on the 21st of May, or at seven on the 5th of June, or at hours intermediate to these on intermediate days.
We again look first for the Great Bear, now near the zenith, and thence find the Pole-star. Turning towards the north, we see Cassiopeia between the Pole-star and the horizon. Towards the north-west is the brilliant Capella, and towards the north-east the equally brilliant Vega, beneath which, and somewhat northerly, is the cross in Cygnus. The Milky Way passes from the eastern horizon towards the north (low down), and so round to the western horizon.
In selecting a region for special observation, we shall adopt a different plan from that used in the preceding “half-hour.” The region on the equator and towards the south is indeed particularly interesting, since it includes the nebular region in Virgo. Within this space nebulae are clustered more closely than over any corresponding space in the heavens, save only the greater Magellanic cloud. But to the observer with telescopes of moderate power these nebulae present few features of special interest; and there are regions of the sky now well situated for observation, which, at most other epochs are either low down towards the horizon or inconveniently near to the zenith. We shall therefore select one of these, the region included in the second map of Plate 2, and the neighbouring part of the celestial sphere.