Julian Date: 2459041.16
2019-2020: CLXXV
THE DAILY ASTRONOMER
Friday, July 10, 2020
Remote Planetarium 63: Week 13 Quiz and Skywatch!
Greetings!
We're adding a new feature to the weekly quiz: a transcript of the Sky Watch Hotline. If you call 207-780-4719, you can hear this recording. It provides listeners with information about the Sun, moon, planets, and other notable celestial events. I will be writing and recording this message each Friday morning. As a few subscribers have asked about the sky calendars, I thought it would be worthwhile to include the Skywatch Hotline transcript. (My apologies for those subscribers outside the Portland area. The times listed are specific to southern Maine.)
Because of the extra space the Sky Watch occupies, the quiz will include sixteen questions instead of twenty.
1. "Mira," a star in the constellation Cetus, literally means ___________
a. "variable"
b. "wonderful"
c. "enigmatic"
d. "reflection."
2. Mira variables are an example of what type of variable star?
a. Algol
b. Cepheid
c. Long period
d. none of the above
3. How massive is a Mira variable?
a. up to two times as massive as the Sun
b. 10 - 20 times more massive than the Sun
c. 25 - 40 times more massive than the Sun
d. 45 - 100 times more massive than the Sun
4. Astronomers divide semi-regular long period variables into how many categories?
a. 2
b. 3
c. 4
d. 5
5. A Type Ia Supernova occurs in a binary star system in which one of the components is a ____________.
a. black hole
b. neutron star
c. white dwarf
d. brown dwarf
6. Why are Type Ia Supernovae useful to determine the distances to remote celestial objects?
a. they are always close
b. Type Ia supernovae are of equal brightness, in theory
c. they only appear in nearby galaxies
d. none of the above. Type Ia Supernovae are not actually useful for distance determination.
7. Type II supernovae occur when a highly massive star explodes from the inside out. This explosion happens after the star accumulates _________ in its core.
a. iron
b. silicon
c. gold
d. silver
8. What is the main difference distinguishing periodic and cataclysmic variables?
a. periodic variables are brighter
b. cataclysmic variables don't reach maxima at regular intervals
c. periodic variables are only found in our galaxy
d. none of the above
9. If a star's parallax angle is 0.1", how far away is it?
a. 1 parsec
b. 10 parsecs
c. 100 parsecs
d. 1000 parsecs
10. The declination of Porrima, a star in Virgo the Maiden, is -01 degrees 26'. Where does Porrima pass directly overhead?
a. just south of the equator
b. just north of the equator
c. along the Tropic of Capricorn
d. along the Arctic Circle
11. The declination of Bellatrix is about +6 degrees. Where in the world would one NOT be able to ever see Bellatrix?
a. anywhere north of 84 degrees north latitude
b. anywhere south of 84 degrees south latitude
c. at the north pole
d. at the equator
12. Which is hotter: a type A star or a type B star?
a. A
b. B
c. their temperatures are equal
d. the question doesn't make sense. The designations A and B do not pertain to temperature.
13. What is meant by "interstellar extinction?"
a. the process by which stars explode
b. the obscuration of stars by interstellar dust
c. the reddening of stars by dust grains
d. none of the above
14. Interstellar dust grains will also make celestial objects appear _________.
a. redder
b. bluer
c. greener
d. more yellowish
15. Along the galactic plane, a star's brightness is reduced by _______ magnitudes per kiloparsec.
a. 1
b. 1.4
c. 1.8
d. 2.6
16. Interstellar extinction affects a star's ______________.
a. absolute magnitude
b. apparent magnitude
c. intrinsic brightness
d. all of the above
e. none of the above
ANSWERS
1. "Mira," a star in the constellation Cetus, literally means ___________
b. "wonderful"
Johannes Hevelius (1611-1687) named the star "Mira," meaning "wonderful" because it seemed to appear and then disappear.
2. Mira variables are an example of what type of variable star?
c. Long period
Mira variables are one of the main type of long period variables, those stars whose variability periods vary between 80 - 1000 days, on average.
3. How massive is a Mira variable?
a. up to two times as massive as the Sun
Mira variables are solar mass stars that are toward the end of their lives.
4. Astronomers divide semi-regular long period variables into how many categories?
c. 4
They designate the categories a, b, c and d.
5. A Type Ia Supernova occurs in a binary star system in which one of the components is a ____________.
c. white dwarf
A Type Ia Supernova occurs when gases from an active star collects onto a white dwarf. When the white dwarf's mass exceeds 1.44 solar masses, it will explode as a Type Ia Supernova.
6. Why are Type Ia supernovae useful to determine the distances to remote celestial objects?
b. Type Ia supernovae are of equal brightness, in theory
Because Type Ia supernovae occur when the white dwarf's mass exceeds 1.44 solar masses, each one should release the same amount of energy and be of equal brightness.
7. Type II supernovae occur when a highly massive star explodes from the inside out. This explosion happens after the star accumulates _________ in its core.
a. iron
Stars can fuse any element up to iron. Iron fusion is an endothermic process, meaning that the amount of energy required to fuse the iron is greater than the energy the fusion reaction imparts onto the star.
8. What is the main difference distinguishing periodic and cataclysmic variables?
b. cataclysmic variables don't reach maxima at regular intervals
Cataclysmic variables flare up often only once or at different times depending on the mechanisms responsible for their variability.
9. If a star's parallax angle is 0.1", how far away is it?
b. 10 parsecs
To determine a star's distance, one must divide the number 1 by the parallax angle expressed in arc-seconds. 1/0.1 = 10 parsecs.
10. The declination of Porrima, a star in Virgo the Maiden, is -01 degrees 26'. Where does Porrima pass directly overhead?
a. just south of the equator
Porrima is located about one and a half degrees south of the celestial equator. Observers one a half degrees south of the Equator will see it pass directly overhead.
11. The declination of Bellatrix is about +6 degrees. Where in the world would one NOT be able to ever see Bellatrix?
b. anywhere south of 84 degrees south latitude
The closer a star appears to the celestial equator, the wider its visibility region. Bellatrix is visible in all regions north of 84 degrees south latitude.
12. Which is hotter: a type A star or a type B star?
b. B
The sequence is as follows
O B A F G K M.
O's are the hottest stars; M the "coolest."
13. What is meant by "interstellar extinction?"
b. the obscuration of stars by interstellar dust
Incoming starlight will be partially obscured by dust grains located within interstellar space. The obscuration relates directly to distance. The more distant the star, the greater the extinction.
14. Interstellar dust grains will also make celestial objects appear _________.
a. redder
The interstellar dust grains are generally equal in size to the wavelength of blue light. So, the blue light within a stream of starlight will often be absorbed or scattered away. Consequently, the incoming light from a celestial object will appear redder than it would were it to pass through a vacuum.
15. Along the galactic plane, a star's brightness is reduced by _______ magnitudes per kiloparsec.
c. 1.8
The interstellar extinction is greatest along the galactic plane where the dust is concentrated.
16. Interstellar extinction affects a star's ______________.
b. apparent magnitude
Apparent magnitude measures a star's apparent brightness. Absolute magnitude refers to a star's intrinsic brightness. Interstellar extinction affects how bright a star appears, but cannot alter a star's actual brightness.
___________________________________________________
SKYWATCH HOTLINE July 10 - 16, 2020
Greeting, Stargazers!
On July 10 the Sun will rise at 5:10 a.m. and set at 8:23 p.m, giving us 15 hours and 13 minutes of daylight, a 13 minute decrease since the Summer Solstice. On July 16, the Sun will rise at 5:15 a.m. and set at 8:19 p.m, providing us with 15 hours and 4 minutes of daylight. The Sun appears to be moving through the constellation Gemini the Twins.
At week's beginning the moon will be progressing through the latter stages of the waning gibbous phase. The moon will be at the last quarter phase on July 12th, and will rise at 12:10 a.m on that date. On July 11, see Mars close to the moon. On July 16th, the waning crescent moon appears to pass close to the Pleiades Star Cluster in Taurus the Bull. One shall see both the moon and cluster in the eastern sky after 2:30 a.m. on the 16th.
The main planetary event this week is the opposition of Jupiter on July 14th. The fifth world will rise at sunset on this date and will remain visible all night. When at opposition, a superior planet -defined as one that is farther from the Sun than Earth- moves to the far side of Earth relative to the Sun. A planet attains its maximum brightness at or around this time. Jupiter's opposition magnitude measures -2.8, making it 3.6 times brighter than Sirius, the night's sky brightest star. (Sirius, incidentally, is not currently visible) Jupiter will continue to progress slowly toward the setting Sun throughout the remainder of 2020 and will vanish into the dusk by year's end.
Mercury rises after 4:35 a.m. and owing to its apparent closeness to the Sun will not be visible this week. Venus, as always the brightest planet, currently occupies the Taurus constellation and will rise just before 3:00 a.m. The optimal time to view Venus is between 4 - 5 a.m, when the brilliant planet remains visible against the intensifying morning twilight. It will be at its maximum brightness of the year on July 10th. At magnitude -4.7, Venus will be thirty times brighter than Sirius. Mars rises almost at midnight. As it is currently located almost precisely on the celestial equator within the constellation Cetus, Mars rises nearly due east and will remain an eastern evening sky object through the rest of the night. At magnitude -0.7, Mars outshines all the stars except Sirius and Canopus, a star not visible at this latitude. Mars will continue to rise earlier and grow brighter as it approaches its next opposition on October 13, 2020. Saturn rises just before 9:00 p.m. in the eastern sky. Even though quite bright by its own standards at magnitude 0.2, Saturn is the dimmest of the naked eye planets this week. Saturn will be at opposition on July 20, 2020. Both Jupiter and Saturn are currently passing through the constellation Sagittarius the Archer.
The main highlight this week is the Comet NEOWISE, named for the Near-Earth Object Wide-Field Infrared Survey Explorer that astronomers used to discover this icy interloper on March 27th. Comet NEOWISE is currently shining at magnitude 1.7 and can be observed low in the eastern pre-dawn sky this week. NEOWISE passed perihelion-its closest point to the Sun- on July 3rd and should brighten. Also, by the end this coming week, NEOWISE will also be visible for approximately one hour after sunset. It is moving currently from the constellation Auriga through Lynx en route to Ursa Major. To see a star chart showing its mid-week location, consult the planetarium's sky watch image web-page at www.usm.maine.edu/planet/sky-watch-hotline On July 22, NEOWISE will attain its minimum distance from Earth, approximately 103 million kilometers. Astronomers do not know how the comet will appear in the coming weeks. Its outgassing could deplete its ice reserves and render it effectively invisible or it could disintegrate in a spectacular outburst. They do know that NEOWISE is an Oort Cloud object moving along an orbit so wide that the comet requires many millennia to complete one circuit around it. After this apparition, NEOWISE is slated to return to Earth's skies in approximately 6,800 years.
Of all the International Space Station flyovers visible to us this week, the brightest will occur in the early morning of July 16th. The ISS will rise at 3:43:01 a.m. in the northwestern sky. It will attain its maximum altitude of 56 degrees and its maximum brightness of magnitude -3.8 at 3:48:26 a.m. and then will set in the southeast at 3:53:49 a.m. Its passage will bring it across Hercules, through the Summer Triangle, along the southern reaches of Pegasus and along Cetus the Whale. Consult the web-page www.usm.maine.edu/planet/sky-watch-hotline to see its path against the stars.
The next transmission of the Sky Watch Hotline is scheduled for July 17, 2020, Julian date 2459048.16. If you would like to contact the Skywatch Hotline, just send an e-mail to [log in to unmask]. Until then, the Southworth Planetarium wishes you beautiful nights, joyous days and clear skies. _______________________________________________________________
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