The star Vega.?

Question

The star Vega has an apparent visual magnitude of 0.03 and the star HR 4374 has an apparent visual magnitude of 4.87. It has been determined that both stars are at the same distance from Earth. What does this information tell us about the two stars?

1. Vega must be closer to Earth than HR 4374.

2. Vega must be farther from Earth than HR 4374.

3. Vega must produce less power than HR 4374.

4. Vega must produce more power than HR 4374.

5. Vega will appear fainter to us than HR 4374.

Answer 1

Vega (pronounced /ˈviːɡə/ or /ˈveɪɡə/; also known as α Lyr / α Lyrae / Alpha Lyrae) is the brightest star in the constellation Lyra, the fifth brightest star in the night sky and the second brightest star in the northern celestial hemisphere, after Arcturus. It is a relatively nearby star at only 25.3 light-years from Earth, and, together with Arcturus and Sirius, one of the most luminous stars in the Sun's neighborhood.

Vega has been extensively studied by astronomers, leading it to be termed, "arguably the next most important star in the sky after the Sun".[9] Historically, Vega served as the northern pole star at about 12,000 BCE and will do so again at around 14,000 CE. Vega was the first star, other than the Sun, to have its photograph taken and the first to have its spectrum photographed. It was also one of the first stars to have its distance estimated through parallax measurements. Vega has served as the baseline for calibrating the photometric brightness scale, and was one of the stars used to define the mean values for the UBV photometric system.

This star is relatively young when compared to the Sun. It has an unusually low abundance of the elements with a higher atomic number than that of helium.[6] Vega is also a suspected variable star that may vary slightly in magnitude in a periodic manner.[10] It is rotating rapidly with a velocity of 274 km/s at the equator. This is causing the equator to bulge outward because of centrifugal effects, and, as a result, there is a variation of temperature across the star's photosphere that reaches a maximum at the poles. From the Earth, Vega is being observed from the direction of one of these poles.[4]

Based upon an excess emission of infrared radiation, Vega has a circumstellar disk of dust. This dust is likely the result of collisions between objects in an orbiting debris disk, which is analogous to the Kuiper belt in the Solar System.[11] Stars that display an infrared excess because of dust emission are termed Vega-like stars.[12] Irregularities in Vega's disk also suggest the presence of at least one planet, likely to be about the size of Jupiter,[13] in orbit around Vega.[14]

Contents [hide]

1 Observation history

2 Visibility

3 Physical properties

3.1 Rotation

3.2 Element abundance

3.3 Kinematics

4 Planetary system

4.1 Infrared excess

4.2 Debris disk

4.3 Possible planets

5 Etymology and cultural significance

6 See also

7 Notes and references

8 External links



[edit] Observation history

Astrophotography, the photography of celestial objects, began in 1840 when John William Draper took an image of the Moon using the daguerreotype process. On July 17, 1850, Vega became the first star (other than the Sun) to be photographed, when it was imaged at the Harvard College Observatory, also with a daguerreotype.[15][16][7] Draper took the first photograph of a star's spectrum in August 1872 when he took an image of Vega, and he also became the first person to show absorption lines in the spectrum of a star.[17] (Similar lines had already been identified in the spectrum of the Sun.)[18] In 1879, William Huggins used photographs of the spectra of Vega and similar stars to identify a set of twelve "very strong lines" that were common to this stellar category. These were later identified as lines from the Hydrogen Balmer series.[19]

The distance to Vega can be determined by measuring its parallax shift against the background stars as the Earth orbits the Sun. The first person to publish a star's parallax was Friedrich G. W. von Struve, when he announced a value of 0.125 arcseconds (0.125″) for Vega.[20] But Friedrich Bessel was skeptical about Struve's data, and, when Bessel published a parallax of 0.314″ for the star system 61 Cygni, Struve revised his value for Vega's parallax to nearly double the original estimate. This change cast further doubt on Struve's data. Thus most astronomers at the time, including Struve, credited Bessel with the first published parallax result. However, Struve's initial result was actually surprisingly close to the currently-accepted value of 0.129″.[21][22]

The brightness of a star, as seen from Earth, is measured with a standardized, logarithmic scale. This apparent magnitude is a numerical value that decreases in value with increasing brightness of the star. The faintest stars visible with the unaided eye are sixth magnitude, while the brightest, Sirius, has magnitude −1.47. To standardize the magnitude scale, astronomers chose Vega to represent magnitude zero at all wavelengths. Thus, for many years, Vega was used as a baseline for the calibration of absolute photometric brightness scales.[23] However, this is no longer the case as the apparent magnitude zero point is now commonly defined in terms of a particular numerically-specified flux. This approach is more convenient for astronomers as Vega is not always available for calibration.[24]

The UBV photometric system measures the magnitude of stars through ultraviolet, blue and yellow filters, producing U, B and V values, respectively. Vega is one of six A0V stars that were used to set the initial mean values for this photometric system when it was introduced in the 1950s. The mean magnitudes for these six stars were defined as: U - B = B - V = 0. In effect, the magnitude of these stars is the same in the yellow, blue and ultraviolet parts of the electromagnetic spectrum.[25] Thus, Vega has a relatively flat electromagnetic spectrum in the visual region—wavelength range 350-850 nanometers, most of which can be seen with the human eye—so the flux densities are roughly equal; 2000-4000 Jy.[26] However, the flux density of Vega drops rapidly in the infrared, and is near 100 Jy at 5 micrometers.[27]

Photometric measurements of Vega during the 1930s appeared to show that the star had a low-magnitude variability on the order of ±0.03 magnitudes. This range of variability was near the limits of observational capability for that time and so the subject of Vega's variability has been controversial. The magnitude of Vega was measured again in 1981 at the David Dunlap Observatory and showed some slight variability. Thus it was suggested that Vega showed occasional low-amplitude pulsations associated with a Delta Scuti variable.[28] This is a category of stars that oscillate in a coherent manner, resulting in periodic pulsations in the star's luminosity.[29] Although Vega fits the physical profile for this type of variable, other observers have found no such variation. Thus the variability may be the result of systematic errors in measurement.[10][30]

In 1983, Vega became the first star found to have a disk of dust. The Infrared Astronomical Satellite (IRAS) discovered an excess of infrared radiation coming from the star, and this was attributed to energy emitted by the orbiting dust as it was heated by the star.[31]

[edit] Visibility

Vega can often be seen near the zenith in the mid-northern latitudes during the evening in the Northern Hemisphere summer.[32] From mid-southern latitudes it can be seen low above the northern horizon during the Southern Hemisphere winter. With a declination of +38.78°, Vega can only be viewed at latitudes north of 51° S. At latitudes to the north of +51° N Vega remains continually above the horizon as a circumpolar star. On about July 1, Vega reaches midnight culmination when it crosses the meridian at that time.[33]



The summer triangle.This star lies at a vertex of a widely-spaced asterism called the Summer Triangle, which consists of the zero-magnitude stars Vega in the constellation Lyra and Altair in Aquila, plus the first magnitude star Deneb in Cygnus.[32] This formation is the approximate shape of a right triangle, with Vega located at its right angle. The Summer Triangle is recognizable in the northern skies for there are few other bright stars in its vicinity.[34]

The Lyrids are a strong meteor shower that peak each year during April 21–22. When a small meteor enters the Earth's atmosphere at a high velocity it produces a streak of light as the object is vaporized. During a shower, a multitude of meteors arrive from the same direction, and, from the perspective of an observer, their glowing trails appear to radiate from a single point in space. In the case of the Lyrids, the meteor trails radiate from the direction of Lyra, and hence are sometimes called the Alpha Lyrids. However, they actually originated from debris emitted by the comet C/1861 G1 Thatcher and have nothing to do with the star.[35]

[edit] Physical properties

Vega's spectral class is A0V, making it a blue-tinged white main sequence star that is fusing hydrogen to helium in its core. Since more massive stars use their fusion fuel more quickly than smaller ones, Vega's main sequence lifetime is only one billion years, a tenth of our Sun's.[36] The current age of this star is between 386 and 511 million years, or up to about half its expected total main sequence life span. After leaving the main sequence, Vega will become a class-M red giant and shed much of its mass, finally becoming a white dwarf. At present Vega has more than twice the mass[4] of the Sun and its full luminosity is about 37 times the Sun's value. If Vega is variable, then it may be a Delta Scuti type with a period of about 0.107 days.[2]

Most of the energy produced at Vega's core is generated by the carbon-nitrogen-oxygen cycle (CNO cycle), a nuclear fusion process that combines protons to form helium nuclei through intermediary nuclei of carbon, nitrogen and oxygen. This process requires a temperature of 16 million K, which is higher than the core temperature of the Sun, but is more efficient than the Sun's proton-proton chain reaction fusion reaction. The CNO cycle is highly temperature sensitive, which results in a con

Answer 2

4

Answer 3

Hint:  Lower numbers are brighter.

That's because "1st magnitude" stars meant significant ones.  "2nd magnitude" meant less significant.  And so on.

Answer 4

magn. diff. =4.87 -0.03 = 4.84

4.84 X 0.4 = 1.936

10^1.936 = 86.3.

Vega is 86.3 times more brilliant than HR 4374 (you said they are at the same distance). So Vega produces more power.

Answer 5

well i don't know anything about magnitudes

but if i had to guess, and it was proven that both r equal distances away form earth, i'd say 5

or 4 if .03 means that we can see it more easier