This Week’s Sky at a Glance, April 30 – May 8

Nova Cassiopeiae 2021 (V1405 Cas) has been regularly rebrightening! It was again as much as magnitude 7.6 on April twenty ninth, matching the luster it wore simply after its March 18th discovery. The dimmest it reached was about magnitude 8.2 via early April.

But the nova has sunk low within the north after dusk. So catch it when it is excessive within the northeast earlier than the beginning of daybreak. For charts see Bright Nova Erupts in Cassiopeia.

Comet ATLAS (C/2020 R4) continues at about ninth magnitude. It’s now passing between Canes Venatici and Coma Berenices conveniently excessive at the hours of darkness night sky, now that the waning Moon rises late. You may have a 6-inch scope. See Make the Most of Comet ATLAS.


■ Have you gone out to greet Mercury and Venus after sundown but? They’re nonetheless fairly low within the west-northwest in brilliant twilight as proven beneath, Venus particularly. So convey binoculars. They’re getting a little simpler daily.

Mercury and Venus after sunset, April 30, 2021
Mercury and Venus are getting simpler to identify via brilliant twilight. These scenes are drawn for a viewer at latitude 40° north, which is the place Mercury and Venus will seem lined up vertically on April thirtieth. At completely different latitudes, you will discover them tilted by about the identical angle that your latitude differs from 40°.

■ As night time descends, look excessive within the west for Pollux and Castor lined up virtually horizontally (relying in your latitude). They type the highest of the big Arch of Spring. To their decrease left is Procyon, the left finish of the Arch. Farther to their decrease proper is the opposite finish, fashioned by Menkalinan (Beta Aurigae) after which sensible Capella.

This spring the Arch has an intruder: little Mars. It’s now about midway from Procyon to Capella.

■ On the opposite aspect of the sky, Arcturus is the brightest star excessive within the east. Spica shines decrease proper of it by about three fists at arm’s size. To the best of Spica by half that distance is the distinctive four-star constellation of Corvus, the springtime Crow, rising into view as night time deepens.


■ Although May has begun, wintry Sirius nonetheless twinkles very low within the west-southwest in twilight. It units quickly after. How for much longer into the spring can you retain Sirius in view? In different phrases, what might be its date of “heliacal setting” as seen by you? The farther north you might be, the earlier Sirius might be gone for the season.


■ In the early daybreak of Monday morning May 3, spot Saturn with the just about last-quarter Moon as proven beneath. Jupiter seems on from their left.

Waning Moon passing under Saturn and Jupiter, May 3-5, 2021
The waning Moon passes below the gas-giant planets as seen in early daybreak.


■ Last-quarter Moon (actual at 3:50 p.m. EDT). The Moon rises very late tonight: round 3 a.m. daylight-saving time Tuesday morning May 4th. Once the Moon is up, it is now Jupiter’s flip to shine to the Moon’s left with dimmer Saturn wanting on from their higher proper.

By the time daybreak of the 4th begins they’re all larger, as proven above.


■ These spring evenings, the lengthy, dim sea serpent Hydra snakes virtually degree far throughout the southern sky.

Find his head, a somewhat dim asterism in regards to the width of your thumb at arm’s size, within the west-southwest. It’s decrease proper of Regulus by about two fists at arm’s size. (Also, a line from Castor via Pollux factors to it about 2½ fists from them.)

Hydra’s brightest star, 2nd-magnitude Alphard, glows as his orange coronary heart lower than two fists left of the top. Hydra’s tail stretches all of the way to Libra rising within the southeast. Hydra’s star sample, from brow to tail-tip, is 95° lengthy.


The Big Dipper now floats degree the other way up proper after darkish, whenever you face north-northeast and look very excessive. Its deal with is on the best. Its Pointer stars, forming the left finish of the Dipper’s bowl, level down towards Polaris.


■ The grand galaxies M81 and M82 are among the many most-sought telescopic targets when the bowl of the Big Dipper is excessive. But have you ever ever tried for the 2 lesser galaxies of their neighborhood, and the 4 double stars right here for newbie scopes? Two of these are straightforward to resolve; two are difficult. See Ken Hewitt-White’s Suburban Stargazer column within the May Sky & Telescope, web page 54.


■ Mercury is now simply noticed in twilight if in case you have a good view to the west-northwest. But Venus, regardless of its brightness, can nonetheless be tough 8° beneath. The visibility of factors in brilliant twilight is exaggerated right here:

The two interior planets regularly grow to be extra insistent about making themselves identified in twilight.

■ Higher within the west as night time falls, little Mars is approaching the bottom of the Arch of Spring: the lengthy line from Procyon on the left to Capella on the best. Mars will stand precisely on this line subsequent Tuesday May eleventh. You can watch its day by day progress towards and throughout this line extra exactly by holding a yardstick or different straightedge to the sky from Procyon to Capella, or by stretching a string tightly from one star to the opposite between your fingers.

Beware of the tough phantasm that a line within the sky that is parallel to the horizon might be a straight line. Nope! The horizon is certainly a great circle across the celestial sphere; so it is straight for a viewer at the middle of the sphere, which means you. But a circle drawn across the sky at some fixed altitude above the horizon might be a small circle, not centered on you, so its rim will seem bent. Severely so throughout a giant span of sky.

Many folks can’t consider that this might be true. That’s why to convey the straightedge or piece of string, somewhat than attempting to evaluate a straight line from Procyon to Capella by eye with the horizon engaging you to make it a reference. Prove it to your self!

■ Summer continues to be seven weeks away, however the Summer Triangle is starting to make its look within the east, one star after one other. The first in view is brilliant Vega. It’s already seen low within the northeast as twilight fades.

Next up is Deneb, decrease left of Vega by a little greater than two fists at arm’s size. Deneb takes about an hour to look after Vega does, relying in your latitude.

The third nook of the triangle is Altair, which exhibits up far to their decrease proper by midnight.


■ A big asterism you could not find out about is the Diamond of Virgo, some 50° tall and increasing over 5 constellations. It now stands upright within the south after the stars come out. Start with Spica, its backside. Upper left from Spica is brilliant Arcturus. Almost as far higher proper from Arcturus is fainter Cor Caroli, third magnitude. The identical distance decrease proper from there may be Denebola, the 2nd-magnitude tailtip of Leo. And then again to Spica.

The backside three of those stars, the brightest, type a almost excellent equilateral triangle. So perhaps we should always name Arcturus, Spica and Denebola the “Spring Triangle” to parallel these of summer season and winter?

In you’ve a darkish sky, or binoculars, look midway from Cor Caroli to Denebola for the very giant, sparse Coma Berenices star cluster. It spans some 4°, in regards to the measurement of a ping-pong ball held at arm’s size.


This Week’s Planet Roundup

Mercury and Venus are rising from deep within the sundown day-to-day. Mercury is highest, as proven within the scenes above, and coming into a wonderful night apparition.

Look early for Venus far beneath it; Venus units earlier than twilight is even half over. Venus shines at magnitude –3.9 all week. Mercury, in contrast, fades this week by virtually half: from magnitude –1.1 to –0.5.

Mars (magnitude +1.6, in Gemini at the texture of the Castor determine) glows within the west proper after darkish. It’s a about halfway between brighter Procyon and Capella. In a telescope it is a mere 4.6 arcseconds huge: simply a tiny brilliant blob.

Jupiter and Saturn (at dim Capricornus) rise greater than an hour earlier than the primary gentle of daybreak. As daybreak begins, spot them within the southeast. Jupiter grabs the attention at magnitude –2.2. Saturn, 16° to Jupiter’s proper or higher proper, is one fifteenth as brilliant at magnitude +0.7.

Jupiter on April 13, 2021
Jupiter on April thirteenth. South right here is up. “I finally had clear skies and better seeing conditions,” writes Christopher Go from his latitude of 10° N. “The Great Red Spot halo is very dark.” And observe the way it curls farther across the Red Spot than in his picture 10 days earlier, beneath.

The South Equatorial Belt following (proper of) the Red Spot is unusually pale. The Equatorial Zone continues to indicate advanced tan patterns throughout its northern two-thirds, and the south fringe of the North Equatorial Belt is darkish red.

Jupiter with Callisto in transit, April 3 2021
An picture by Go from April third. The darkish dot isn’t a moon’s shadow however darkish Callisto itself, caught in a uncommon equatorial transit throughout Jupiter.

Uranus and Neptune are hidden within the glare of the Sun.

All descriptions that relate to your horizon — together with the phrases up, down, proper, and left — are written for the world’s mid-northern latitudes. Descriptions that additionally rely on longitude (primarily Moon positions) are for North America.

Eastern Daylight Time, EDT, is Universal Time minus 4 hours. Universal Time is also referred to as UT, UTC, GMT, or Z time. To grow to be extra knowledgeable about time methods than 99% of the folks you will ever meet, see our compact article Time and the Amateur Astronomer.

Want to grow to be a higher astronomer? Learn your way across the constellations. They’re the important thing to finding all the pieces fainter and deeper to hunt with binoculars or a telescope.

This is an out of doors nature passion. For an easy-to-use constellation information masking the entire night sky, use the large month-to-month map within the middle of every problem of Sky & Telescope, the important journal of astronomy.

Once you get a telescope, to place it to good use you will want a detailed, large-scale sky atlas (set of charts). The fundamental normal is the Pocket Sky Atlas (in both the original or Jumbo Edition), which exhibits stars to magnitude 7.6.

Pocket Sky Atlas cover, Jumbo edition
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and tons of of telescopic galaxies, star clusters, and nebulae amongst them. Shown right here is the Jumbo Edition, which is in onerous covers and enlarged for simpler studying outside by red flashlight. Sample charts. More about the current editions.

Next up is the bigger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; almost 3 times as many. The subsequent up, as soon as you understand your way round, are the even bigger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And you’ll want to learn how to use sky charts with a telescope.

You’ll additionally need a good deep-sky guidebook, comparable to Sky Atlas 2000.0 Companion by Strong and Sinnott, or the larger (and illustrated) Night Sky Observer’s Guide by Kepple and Sanner.

Can a computerized telescope change charts? Not for freshmen, I do not assume, and never on mounts and tripods which might be lower than top-quality mechanically, which means heavy and costly. And as Terence Dickinson and Alan Dyer say of their Backyard Astronomer’s Guide, “A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand.”

(*8*)Audio sky tour. Out below the night sky together with your
earbuds in place, take heed to Kelly Beatty’s month-to-month
podcast tour of the heavens above. It’s free.

“The dangers of not thinking clearly are much greater now than ever before. It’s not that there’s something new in our way of thinking, it’s that credulous and confused thinking can be much more lethal in ways it was never before.”
            — Carl Sagan, 1996

“Facts are stubborn things.”
            — John Adams, 1770

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