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IOAA 2025, Наблюдения, звездни карти (OM) — Задача 2. Know your Grid

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Всички материали от IOAA 2025

OM02: Solution and Marking Scheme · 16 т.

Условие

Use the skymap “Map-OM02” to answer the questions below.

The constellation lines and boundaries (as per IAU standards) of two constellations denoted as C1 and C2 are shown in the full-sky map. Alternative depictions of the same constellations according to a few cultures are also shown on the right panel for your reference, if needed. A certain coordinate grid is also shown.

(OM02.1) Identify the constellations C1 and C2 and write their names (of Latin origin) or IAU abbreviations in the table in the Summary Answersheet. [1 т.]

(OM02.2) Three empty red squares and three empty blue circles are shown on the map. There is a grid line passing through each of these squares and circles.

(OM02.2a) The lines that pass through the red squares are lines of constant
Ecliptic latitude ( $\beta$ ) / Ecliptic longitude ( $\lambda$ ) / Declination ( $\delta$ ) / Right Ascension ( $\alpha$ ) / Galactic latitude ( $b$ ) / Galactic longitude ( $l$ ).
Tick (✓) the correct option in the Summary Answersheet. [1 т.]

(OM02.2b) The lines that pass through the blue circles are lines of constant
Ecliptic latitude ( $\beta$ ) / Ecliptic longitude ( $\lambda$ ) / Declination ( $\delta$ ) / Right Ascension ( $\alpha$ ) / Galactic latitude ( $b$ ) / Galactic longitude ( $l$ ).
Tick (✓) the correct option in the Summary Answersheet. [1 т.]

(OM02.3) Identify the North and South poles of the grid. Label these points as “N” and “S”, respectively on the map “Map-OM02”. [1 т.]

(OM02.4) Two of the following are present in the given sky map. Identify these by marking with appropriate symbols (shown below) on the corresponding entire curve/line.

(i) Ecliptic (small bars like $-\!\!+\!\!-\!\!+\!\!-\!\!+\!\!-$ )

(ii) Celestial Equator (small circles like $-\!\circ\!-\!\circ\!-\!\circ\!-$ )

(iii) Galactic Equator (small crosses like $-\!\!\times\!\!-\!\!\times\!\!-\!\!\times\!\!-$ ) [2 т.]

(OM02.5) Mark the Vernal Equinox (VE) and Autumnal Equinox (AE) on the grid with $\otimes$ and write VE and AE beside them, respectively. [2 т.]

(OM02.6) Indicate the direction of the Sun’s annual motion by drawing an arrow close to the Vernal Equinox. [1 т.]

(OM02.7) Write the values, in appropriate units, inside each red square and blue circle given on the “Map-OM02”, of the corresponding grid lines passing through them. [3 т.]

(OM02.8) The location of 4 constellations (apart from C1 and C2) are shown on the grid by light-green shaded areas. Consider the following list of constellations.

Aquarius (Aqr), Cygnus (Cyg), Leo (Leo), Orion (Ori), Perseus (Per), Sagittarius (Sgr).

On the map “Map-OM02”, label the appropriate shaded areas with the IAU abbreviations of the constellations that are present in the above list. Mark a cross ( $\times$ ) on those shaded areas, if any, which do not appear in the above list. [4 т.]

Отговори

Решение

(OM02.1)

It is evident from the constellation lines and their relative positions that –
C1 : Virgo or Vir
C2 : Corvus or Crv

Correct identification of each constellation	0.5

(OM02.2a)

Since the constellation boundaries are parallel to the grid lines, the grid shown in the figure must be the Equatorial Grid.
Circles of declination are centred around the poles. Hence, the lines that pass through red squares are declination ( $\boxed{\delta}$ ) lines.

Correction identification	1.0

(OM02.2b)

Lines emanating from poles and perpendicular to the declination circles are RA lines. Hence, the lines that pass through the blue circles are lines of constant RA ( $\boxed{\alpha}$ ).

Correction identification	1.0

(OM02.3)

Constellation of Corvus is towards the South of Virgo. Hence, the pole of the hemisphere in which Corvus lies is the South pole.

Correct identification of each pole	0.5

(OM02.4)

Ecliptic marked correctly	1.0
Celestial Equator marked correctly	1.0
If only one segment of Celestial Equator is marked	0.5

(OM02.5)

Equinoxes are intersection points of the equator and ecliptic. Autumnal equinox (AE) lies in the constellation of Virgo. Hence the other intersection point is Vernal equinox (VE).

Equinoxes are marked at intersections of CE and Ecliptic	1.0
Correctly identified of both the equinoxes	1.0

(OM02.6)

From VE the Sun moves northward, Sun’s motion is in the direction of increasing RA.

Correct direction	1.0

(OM02.7)

The Vernal Equinox (VE) and Autumnal Equinox (AE) are identified in part (OM02.5). The Right Ascension (RA) of the VE is $0\,\mathrm{h}$ , while the RA of the AE is $12\,\mathrm{h}$ . From part (OM02.6), it is seen that the Sun moves northward in the direction of increasing RA, which allows the RA circles to be marked accordingly. RA is conventionally measured in hours, minutes, and seconds.

The celestial pole has a declination of $90^{\circ}$ , with the convention that northern declinations are considered positive and southern declinations are considered negative. Declinations are measured in degrees, arcminutes, and arcseconds.

Solution for (OM02.7): the same map with the values written in green: red squares +20°, -10° and -30°; blue circles 20h, 10h and 7h.

Each correct value with appropriate sign and in appropriate units	0.5
Incorrect values but with appropriate sign and units and consistent with (OM02.2a) and (OM02.2b) – maximum	1.5

(OM02.8)

In the given list there are 3 zodiacal constellations, Aquarius, Leo and Sagittarius, which implies that they should lie on the Ecliptic.
The Ecliptic passes through the constellation to the top left which is about 2 hours ahead in RA from Virgo, hence it is Sagittarius.
From the given list Leo and Orion are the constellations which lie on the Celestial Equator. Hence, the constellation on the lower right has to be Orion.
Out of the remaining constellations, i.e. Perseus and Cygnus, the constellation of Cygnus lies between RA 20h and 22h.
The remaining box is of Ursa Major which is not present in the given list.

Each correct identification (including marking $\times$ , or “UMa”)	1.0

Solution for (OM02.8): the same map with the light-green shaded areas labelled Sgr (top left), Cyg (top centre-right), Ori (lower right) and a large green X on the remaining area.

Оригинал в Архива: Observation-SkyMap-Questions.pdf · официални решения: Observation-SkyMap-Solutions.pdf