SCOPE ON THE SKIES Occultations and eclipses BY BOB RIDDLE n astronomy, an occultation oc- the viewing area of a solar eclipse surface. If you are not within the curs when something between but not within the path of the path, then you may experience a Iyou and a distant object blocks Moon’s shadow, you will only grazing occultation or a conjunc- your view of that distant object. see a partial eclipse of the Sun. tion, depending on your distance Occultations are regular, pre- Viewing an occultation of a from the path of occultation. Lu- dictable events because planets, star has a similar geographic re- nar conjunctions occur when the dwarf planets, moons, and as- quirement. However, to view a Moon is within a few degrees of teroids orbit the Sun and pass in total solar eclipse, you must be a planet or star, while planetary front of stars in the background. within the 100- to 274-kilometer- conjunctions occur when a planet Our Moon occults, or eclipses, wide (60 to 170 mi) shadow of is within a few degrees from a the Sun four to six times each the Moon. To view an occultation star or planet. But there are ex- year. If you are within the path of of a star, you must be within a ceptions. During the July 2011 the Moon’s shadow, you will see path of occultation that is only a occultation of the star LQ Aquarii a total eclipse. If you are within few miles wide along the Earth’s by Double Asteroid 90 Antiope, | FIGURE 1: March occultation dates Solar system object Date Occultation path maps Saturn March 1 https://bit.ly/2sjUU6k Dwarf planet Pluto March 2 https://bit.ly/2RqYKth Asteroid 2 Pallas March 3 http://asteroidoccultation.com/2019_03/0303_2_59440_Map.gif Asteroid 21 Lutetia https://bit.ly/2AIgfLe Asteroid 3 Juno March 3 http://asteroidoccultation.com/2019_03/0303_3_59444_Map.gif Dwarf planet Makemake March 9 http://asteroidoccultation.com/2019_03/0309_136472_59488_Map.gif Asteroid 358 Apollonia March 19 http://asteroidoccultation.com/2019_03/0319_358_62626_Map.gif Asteroid 2 Pallas March 21 http://asteroidoccultation.com/2019_03/0321_2_59602_Map.gif Saturn March 29 https://bit.ly/2FlnCMO Dwarf planet Pluto March 29 https://bit.ly/2M4UmdH Asteroid 21 Lutetia March 31 https://bit.ly/2AIgfLe 20 the occultation path was up to then after the star was behind didates as well. Farther away 125 miles (200 km) wide. the disk of the planet (see Re- from the ecliptic, where many Unlike a solar eclipse, there is sources). Similarly, comparing asteroid orbital paths are locat- no shadow path in occultations. observations from different lo- ed, stars are regularly occulted So, what do you see? Because cations along the path of stellar by asteroids. planets appear star-like when occultations has also allowed us either is occulted, they disap- to determine the shape of dis- pear from view as the occulting tant asteroids (see “The Shape of Occultations in March object passes across our line of Things” in Resources). 2019 sight. The length of the occul- Every month, our Moon and Several occultations occur this tation depends on the apparent asteroids are usually involved month, including two lunar oc- size of the occulting object and with occultations and conjunc- cultations with the planet Sat- the angle it moves at relative to tions, often with the same stars urn, dwarf planet Pluto, and the star being occulted. The star and planets on a regular basis. two asteroids (see Figure 1). reappears on the opposite side The Moon’s orbital path is tilted These occultations are at the be- of the occulting object moments about 6° from the Earth’s orbit, ginning and end of the month. or minutes later. called the ecliptic, so the Moon Several asteroids also have oc- Observing occultations plays is always somewhere close to or cultations with stars this month. an important role in astronomy. on the ecliptic. Several stars are While none of these occultations In possibly the most famous also on or near the ecliptic and are visible from our part of the stellar occultation, rings were may cause an occultation or con- Earth, students could examine discovered around the planet junction. The seven other plan- the occultation path to generate Uranus during its occultation ets have orbital path inclinations interests in observing an occul- of a distant star. As Uranus oc- ranging from 0.77 for Uranus to tation, or learn more about the culted, the light from the star 7.01 for Mercury, making them countries along the path of the flickered on and off before and occultation and conjunction can- ecliptic (see Figure 2). | FIGURE 2: Path of the ecliptic March 2019 21 | FIGURE 3: Table of some solar system objects with moons The moons in our solar Name and type of object Number and names of moons system Asteroid Ida 1: Dactyl An eclipse involving the Earth, our Moon, and the Sun is deter- Asteroid Eugenia 1: Petit-Prince mined by the arrangement of the Asteroid Pulcova (double asteroid) 1: S/2000 (762) 1 three objects. All Sun-orbiting Dwarf planet Pluto 5: Charon; Nix; Hydra; Kerberos; Styx objects with moons will, at some Dwarf planet Haumea 2: Hi’iaka; Namaka point in their respective orbit, experience eclipses of the Sun by its moon. Planets are not the March only objects with moons; many minor planets (including aster- 1 Moon occultation with 16 Moon at ascending node oids, dwarf planets, and Kuiper Saturn 17 Waxing gibbous Moon near belt objects) have a moon. There 2 Moon at descending node Beehive open star cluster are currently around 330 moons Waning crescent Moon 18 Waxing gibbous Moon near discovered in orbit around vari- close to Venus Regulus ous minor planets, including 143 Moon occultation with 19 Moon at perigee: 359,381 main belt asteroids and 63 near- Pluto km (223,309 mi.) Earth asteroids. Some of the mi- 3 Moon occultation with Asteroid 358 Apollonia nor planets have more than one Asteroid 21 Lutetia occultation with HIP 19036 moon, while dwarf planet Pluto Asteroid 2 Pallas (star) has five moons. Minor planets occultation with TYC 0323- 20 March equinox (21:58 with a moon are known as binary 01028-1 (star) UT–5:58 pm EDT) minor planets, while those with Asteroid 3 Juno occultation 21 Full Moon (a Super Moon) three moons are known as trinary with UCAC5 492-007098 Asteroid 2 Pallas minor planets. (star) occultation with UCAC5 In 1994, during the Galileo mis- 4 Moon at apogee: 406,391 510-053447 (star) sion to Jupiter, the first asteroid km (252,520 mi.) 23 Martian summer solstice with a moon was discovered. As 6 New Moon 27 Waning gibbous Moon near the spacecraft passed through the 7 Neptune in conjunction Jupiter main asteroid belt it took images with Sun 28 Last quarter Moon of the asteroid Ida and its one- 9 Dwarf planet Makemake 29 Moon occultation with mile-long (1.6 km) moon, which occultation with UCAC5 Saturn was later named Dactyl (see Fig- 572-047492 (Star) Moon occultation with ure 3). When the size difference 10 Begin Daylight Savings Pluto between the objects is large, (Ida Time Moon at descending node is 10 miles (16 km) long) the larg- 11 Waxing crescent Moon near 31 Mars near Pleiades open er object is sometimes called the Mars star cluster primary and the smaller called 13 Waxing crescent Moon near Moon occultation with the secondary. If the objects are Aldebaran Asteroid 21 Lutetia about the same size, it could be 14 First quarter Moon Begin European Summer called a double asteroid. Pi Day Time (set clocks ahead one The number of moons orbit- 15 Mercury at inferior hour.) ing the eight planets in our solar conjunction system changes sporadically, as 22 SCOPE ON THE SKIES new discoveries are made from examining mission data or from current observations. Recently, For students another 12 moons orbiting Ju- 1. Celestial objects are given temporary names upon discovery and piter were discovered, bringing eventually a permanent name. Certain rules are followed for nam- that planet’s known moon total ing planets and moons. What is the connection between the names to 79 (see Figure 4). Two of the of Asteroid Ida and its moon Dactyl? (In Greek mythology Ida lived eight planets, inner planets Mer- on the island of Crete and helped raise Zeus. The moon Dactyl was cury and Venus, do not have named after a group of men, the Dactyls, who lived on Mount Ida.) any orbiting natural satellites. 2. Download the free SFA equatorial star charts (see Resources). It is thought that gravity plays Tape maps 2 and 3 together so you can see the entire ecliptic path. an important role in why these Obtain daily Moon coordinate positions from the U.S. Navy Obser- two planets do not have a moon. vatory website (see Resources) and then use the right ascension They are too close to the Sun, and declination to plot and follow the Moon. and it is likely that any moon that may have formed with the planet or inbound from the outer solar system would be caught in the more powerful gravitational Visible planets field of the Sun and pulled into Mercury will appear in the morning skies over the eastern hori- the Sun. • zon during the last half of the month. Venus will be low but still bright and very visible over the east- ern horizon at sunrise. Watch for a close conjunction with the | FIGURE 4: The current Moon on the first of March. number of moons surrounding eight planets Mars will be visible over the southwestern horizon and will move within 1° to 2° from the open star cluster the Pleiades by Name of Number of the end of the month.