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Morrison Planetarium's hub for the latest out-of-this-world news, from meteor showers to space exploration events.
Sunrise | Solar Noon | Sunset
6:55 am | 1:13 pm | 7:33 pm
Sunrise | Solar Noon | Sunset
6:14 am | 1:06 pm | 8:00 pm
Sunrise | Solar Noon | Sunset
5:50 am | 1:07 pm | 8:26 pm
(All times are PDT for San Francisco, CA, and will vary slightly for other locations.)
Notes for Spring
April 12 is the 57th anniversary of Yuri Gagarin's history-making flight aboard the USSR's Vostok 1 that made him the first human to fly into space. Since 2001, this achievement has been observed as a "World Space Party" called "Yuri's Night" in Gagarin's honor.
The goal of Yuri's Night is to celebrate humanity's past, present, and future in space through education and outreach events ranging from tech-and-techno festivals at NASA Centers, to movie showings and stargazing sessions, and to science talks, music, and art presentations at programs such as the Academy's own NightLife.
But wait—there's more celebrating to do: April 21 is the 45th annual Astronomy Day, founded in 1973 by the Astronomical Association of Northern California and since expanded to a celebration of stargazing in a day of presentations, demonstrations, and observations dedicated to increasing public appreciation of astronomy.
The Academy is observing the day with partners from the Astronomical Society of the Pacific, the San Francisco Amateur Astronomers, the Eastbay Astronomical Society, Novato's Space Station Museum, Robert Ferguson Observatory, San Francisco State University, City College of San Francisco, and more. In the evening, weather permitting, some organizations and sidewalk astronomers will set up telescopes at selected locations so that passersby can observe the first quarter Moon and the planet Venus.
Sprinkles of comet dust rain through the sky this season as numerous meteor showers light up the night—although not by much, in most cases. The notable highlights of the season start with the Lyrids in April.
The Lyrids are a modest display, active from April 19-24 and peaking on the 21st-22nd. Named after the constellation Lyra the Harp, from which about 10 meteors per hour appear to radiate, this display has surprised observers with unexpected outbursts of around 100 per hour in 1922, 1945, and 1982. This year, the peak of the shower coincides with a first quarter Moon, which—even though only 1/10th as bright as a full Moon—may be enough light to wash about half the meteors from view, so expect about 3-5 meteors per hour, even away from city lights. Slightly more might be seen after moonset in the early hours of the 22nd.
This shower occurs as Earth passes through the trail of Comet C/1861 G1 Thatcher, which was discovered in 1861, but the link between meteor showers and comets wasn't made until several years later. Particles of dust along the comet's orbit are swept up by Earth as it plows through the trail at slightly more than 108,000 kilometers (67,000 miles) per hour, or about 30 kilometers (18.6 miles) per second. As the particle enters the atmosphere, it's moving too fast for air molecules to get out of the way, causing a ram-pressure that heats the compressed air to several thousand degrees Fahrenheit. This incinerates the particle in a bright flash of light—a meteor (or "shooting star," as some still call them). However, the shower itself is the oldest-known of all the meteor displays, with Chinese observations dating back 2,600 years, to 687 BC.
Eta Aquarid Shower
Earth crosses Halley's in May and again in October, but we'll focus here on the Eta Aquarids, which are active April 21-May 12, peaking on May 4-5. This is actually a better display for observers in the Southern Hemisphere, for whom the shower's radiant (the point in the sky from which meteors appear to radiate) is visible a little longer than for skywatchers north of the equator, where the radiant rises only about an hour before the start of morning twilight.
However, this year's peak occurs when the Moon is at a waning gibbous phase, so moonlight might wash fainter meteors from view.
The giant planet Jupiter reaches opposition on May 8, marking the middle of the best time to observe the largest world in our solar system.
Jupiter is so large that from 658 million kilometers (409 million miles), its 11-Earths-wide disk is visible in binoculars, as are its four largest moons if the binoculars are steadily mounted.
Through telescopes, Jupiter's chemical-stained atmosphere is festooned with dark belts and light zones that wrap around the planet, and every 10 hours, its most famous bauble—the Great Red Spot—rotates into view. This baffling feature is most often compared to a hurricane that has been observed on and off since 1665, and continuously since 1830. It's still uncertain whether the same object was observed during those periods, because it has changed latitude, color-intensity, and size over time.
Saturn reaches opposition on June 27 and is located on the same side of the Sun as Earth.
In-the-know stargazers watch for something called the "opposition surge" or "Seeliger effect," which makes Saturn's rings appear a little brighter. This is because not only is a planet at opposition closest to Earth, appearing larger, but also because no shadows are visible from Earth's point of view (which is the same angle from which sunlight is shining on Saturn). This causes a slight increase in overall brightness.
Another phenomenon called "coherent backscattering" adds to the brightness, caused by the cumulative effect of multiple reflections of light from the countless tiny ice particles comprising Saturn's rings.
Mars is starting to look pretty good in the night sky, and its best is yet to come. Presently, the Red Planet is located in the south an hour before dawn—very close to Saturn in early April, after which they slowly separate. It reaches opposition on July 26, which is when Earth and Mars are on the same side of the Sun and the closest they have been to each other since 2003, when they were 55.7 million kilometers (34.6 million miles) apart.
At opposition, Mars is at its brightest, and in 2003 a lot of people got carried away with that and exaggerated what Mars was expected to look like, with some claiming that it would look "as big as the Moon." (It didn't). This time around, at a distance of 75.3 million kilometers (46.8 million miles), Mars won't be as close as it was 15 years ago, and will be too small for the unaided eye to resolve as more than just a bright dot. So, if you hear any hype about it being a "once-in-a-lifetime," Moon-size spectacle, don't fall for it.
NASA and other space agencies plan launches around the time Earth and Mars are at opposition to minimize the distance that spacecraft have to travel. The next Mars-bound vehicle scheduled for launch is NASA's InSight lander (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport—whoever thinks these names up deserves a cookie). At this writing, it's set to lift off in May or June and is expected to land in the Elysium Planitia region in late-November.
June 21 marks the summer solstice in the Northern Hemisphere, when the Sun rises and sets farthest-north along the horizon, reaching its highest elevation at midday. Because of its high arc across the sky, this is when the Sun is above the horizon longer than on any other day of the year, leading many to refer to it as the "longest day"—although perhaps "longest daytime" would be more accurate.
Traditionally, the Sun is highest when it crosses the meridian, which is the imaginary line running straight overhead from north to south. This point was known in Latin as "meridiem," or midday, otherwise known as noon. That's where we get the terms "am" (ante-meridian, or before noon) and "pm" (post-meridian, or after noon).
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The Benjamin Dean lecture series brings the world's leading experts in astronomy, astrophysics, and more to the Academy's Morrison Planetarium.